Cancers

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3 pages, 186 KiB

Open AccessEditorial

PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer

by Nicola Curtin and Péter Bai

Cancers 2020, 12(12), 3494; https://doi.org/10.3390/cancers12123494 - 24 Nov 2020

Cited by 2 | Viewed by 2076

Abstract

The role of poly(ADP-ribose) polymerase-1 (PARP1) in DNA repair and as a potential target for anticancer therapy has been under investigation for more than 50 years [...] Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

Research

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21 pages, 2926 KiB

Open AccessArticle

Targeting Nuclear NAD⁺ Synthesis Inhibits DNA Repair, Impairs Metabolic Adaptation and Increases Chemosensitivity of U-2OS Osteosarcoma Cells

by Alexandra Kiss, Arnold Péter Ráduly, Zsolt Regdon, Zsuzsanna Polgár, Szabolcs Tarapcsák, Isotta Sturniolo, Tarek El‐Hamoly, László Virág and Csaba Hegedűs

Cancers 2020, 12(5), 1180; https://doi.org/10.3390/cancers12051180 - 7 May 2020

Cited by 26 | Viewed by 4890

Abstract

Osteosarcoma (OS) is the most common bone tumor in children and adolescents. Modern OS treatment, based on the combination of neoadjuvant chemotherapy (cisplatin + doxorubicin + methotrexate) with subsequent surgical removal of the primary tumor and metastases, has dramatically improved overall survival of [...] Read more.

Osteosarcoma (OS) is the most common bone tumor in children and adolescents. Modern OS treatment, based on the combination of neoadjuvant chemotherapy (cisplatin + doxorubicin + methotrexate) with subsequent surgical removal of the primary tumor and metastases, has dramatically improved overall survival of OS patients. However, further research is needed to identify new therapeutic targets. Here we report that expression level of the nuclear NAD synthesis enzyme, nicotinamide mononucleotide adenylyltransferase-1 (NMNAT1), increases in U-2OS cells upon exposure to DNA damaging agents, suggesting the involvement of the enzyme in the DNA damage response. Moreover, genetic inactivation of NMNAT1 sensitizes U-2OS osteosarcoma cells to cisplatin, doxorubicin, or a combination of these two treatments. Increased cisplatin-induced cell death of NMNAT1^−/− cells showed features of both apoptosis and necroptosis, as indicated by the protective effect of the caspase-3 inhibitor z-DEVD-FMK and the necroptosis inhibitor necrostatin-1. Activation of the DNA damage sensor enzyme poly(ADP-ribose) polymerase 1 (PARP1), a major consumer of NAD⁺ in the nucleus, was fully blocked by NMNAT1 inactivation, leading to increased DNA damage (phospho-H2AX foci). The PARP inhibitor, olaparib, sensitized wild type but not NMNAT1^−/− cells to cisplatin-induced anti-clonogenic effects, suggesting that impaired PARP1 activity is important for chemosensitization. Cisplatin-induced cell death of NMNAT1^−/− cells was also characterized by a marked drop in cellular ATP levels and impaired mitochondrial respiratory reserve capacity, highlighting the central role of compromised cellular bioenergetics in chemosensitization by NMNAT1 inactivation. Moreover, NMNAT1 cells also displayed markedly higher sensitivity to cisplatin when grown as spheroids in 3D culture. In summary, our work provides the first evidence that NMNAT1 is a promising therapeutic target for osteosarcoma and possibly other tumors as well. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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17 pages, 2766 KiB

Open AccessArticle

ATR Inhibition Potentiates PARP Inhibitor Cytotoxicity in High Risk Neuroblastoma Cell Lines by Multiple Mechanisms

by Harriet E. D. Southgate, Lindi Chen, Deborah A. Tweddle and Nicola J. Curtin

Cancers 2020, 12(5), 1095; https://doi.org/10.3390/cancers12051095 - 28 Apr 2020

Cited by 24 | Viewed by 5357

Abstract

Background: High risk neuroblastoma (HR-NB) is one the most difficult childhood cancers to cure. These tumours frequently present with DNA damage response (DDR) defects including loss or mutation of key DDR genes, oncogene-induced replication stress (RS) and cell cycle checkpoint dysfunction. Aim: To [...] Read more.

Background: High risk neuroblastoma (HR-NB) is one the most difficult childhood cancers to cure. These tumours frequently present with DNA damage response (DDR) defects including loss or mutation of key DDR genes, oncogene-induced replication stress (RS) and cell cycle checkpoint dysfunction. Aim: To identify biomarkers of sensitivity to inhibition of Ataxia telangiectasia and Rad3 related (ATR), a DNA damage sensor, and poly (ADP-ribose) polymerase (PARP), which is required for single strand break repair. We also hypothesise that combining ATR and PARP inhibition is synergistic. Methods: Single agent sensitivity to VE-821 (ATR inhibitor) and olaparib (PARP inhibitor), and the combination, was determined using cell proliferation and clonogenic assays, in HR-NB cell lines. Basal expression of DDR proteins, including ataxia telangiectasia mutated (ATM) and ATR, was assessed using Western blotting. CHK1^S345 and H2AX^S129 phosphorylation was assessed using Western blotting to determine ATR activity and RS, respectively. RS and homologous recombination repair (HRR) activity was also measured by γH2AX and Rad51 foci formation using immunofluorescence. Results: MYCN amplification and/or low ATM protein expression were associated with sensitivity to VE-821 (p < 0.05). VE-821 was synergistic with olaparib (CI value 0.04–0.89) independent of MYCN or ATM status. Olaparib increased H2AX^S129 phosphorylation which was further increased by VE-821. Olaparib-induced Rad51 foci formation was reduced by VE-821 suggesting inhibition of HRR. Conclusion: RS associated with MYCN amplification, ATR loss or PARP inhibition increases sensitivity to the ATR inhibitor VE-821. These findings suggest a potential therapeutic strategy for the treatment of HR-NB. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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14 pages, 3251 KiB

Open AccessArticle

Reduced Tumorigenicity of Mouse ES Cells and the Augmented Anti-Tumor Therapeutic Effects under Parg Deficiency

by Yuki Sonoda, Yuka Sasaki, Akemi Gunji, Hidenori Shirai, Tomonori Araki, Shoji Imamichi, Takae Onodera, Anna-Margareta Rydén, Masatoshi Watanabe, Jun Itami, Takuya Honda, Kazuto Ashizawa, Kazuhiko Nakao and Mitsuko Masutani

Cancers 2020, 12(4), 1056; https://doi.org/10.3390/cancers12041056 - 24 Apr 2020

Cited by 4 | Viewed by 2785

Abstract

PolyADP-ribosylation is a post-translational modification of proteins, and poly(ADP-ribose) (PAR) polymerase (PARP) family proteins synthesize PAR using NAD as a substrate. Poly(ADP-ribose) glycohydrolase (PARG) functions as the main enzyme for the degradation of PAR. In this study, we investigated the effects of Parg [...] Read more.

PolyADP-ribosylation is a post-translational modification of proteins, and poly(ADP-ribose) (PAR) polymerase (PARP) family proteins synthesize PAR using NAD as a substrate. Poly(ADP-ribose) glycohydrolase (PARG) functions as the main enzyme for the degradation of PAR. In this study, we investigated the effects of Parg deficiency on tumorigenesis and therapeutic efficacy of DNA damaging agents, using mouse ES cell-derived tumor models. To examine the effects of Parg deficiency on tumorigenesis, Parg^+/+ and Parg^−/− ES cells were subcutaneously injected into nude mice. The results showed that Parg deficiency delays early onset of tumorigenesis from ES cells. All the tumors were phenotypically similar to teratocarcinoma and microscopic findings indicated that differentiation spectrum was similar between the Parg genotypes. The augmented anti-tumor therapeutic effects of X-irradiation were observed under Parg deficiency. These results suggest that Parg deficiency suppresses early stages of tumorigenesis and that Parg inhibition, in combination with DNA damaging agents, may efficiently control tumor growth in particular types of germ cell tumors. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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14 pages, 3041 KiB

Open AccessArticle

Exploring the Synergy between PARP and CHK1 Inhibition in Matched BRCA2 Mutant and Corrected Cells

by Hannah L Smith, Lisa Prendergast and Nicola J Curtin

Cancers 2020, 12(4), 878; https://doi.org/10.3390/cancers12040878 - 4 Apr 2020

Cited by 17 | Viewed by 3826

Abstract

PARP inhibition results in the accumulation of DNA SSBs, causing replication stress (RS) and lesions that can only be resolved by homologous recombination repair (HRR). Defects in HRR, e.g., due to BRCA2 mutation, confer profound sensitivity to PARP inhibitor (PARPi) cytotoxicity. In response [...] Read more.

PARP inhibition results in the accumulation of DNA SSBs, causing replication stress (RS) and lesions that can only be resolved by homologous recombination repair (HRR). Defects in HRR, e.g., due to BRCA2 mutation, confer profound sensitivity to PARP inhibitor (PARPi) cytotoxicity. In response to RS, CHK1 is activated to signal to S and G2/M cell cycle checkpoints and also to HRR. To determine the relative contribution of these two functions of CHK1 to survival following PARPi exposure, we investigated the effects of rucaparib (a PARPi) and PF-477736 (a CHK1 inhibitor) alone and in combination in cells with mutated and corrected BRCA2. The BRCA2 mutated V-C8 cells were 1000× more sensitive to rucaparib cytotoxicity than their matched BRCA2 corrected V-C8.B2 cells, but no more sensitive to PF-477736 despite having seven-fold higher levels of RS. PF-477736 caused a five-fold enhancement of rucaparib cytotoxicity in the V-C8.B2 cells, but no enhancement in the V-C8 cells. This differential sensitivity was not due to a difference in PARP1 or CHK1 expression or activity. PF-477736 increased rucaparib-induced RS (γH2AX foci) and completely inhibited RAD51 focus formation, indicating a profound suppression of HRR. Our data suggested that inhibition of HRR was the main mechanism of sensitisation to rucaparib, compounded with an inhibition of cell cycle checkpoints by PF-477736. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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19 pages, 6349 KiB

Open AccessArticle

Synergistic Anti-Tumour Effect of Syk Inhibitor and Olaparib in Squamous Cell Carcinoma: Roles of Syk in EGFR Signalling and PARP1 Activation

by Duen-Yi Huang, Wei-Yu Chen, Chi-Long Chen, Nan-Lin Wu and Wan-Wan Lin

Cancers 2020, 12(2), 489; https://doi.org/10.3390/cancers12020489 - 19 Feb 2020

Cited by 9 | Viewed by 3826

Abstract

Syk is a non-receptor tyrosine kinase involved in the signalling of immunoreceptors and growth factor receptors. Previously, we reported that Syk mediates epidermal growth factor receptor (EGFR) signalling and plays a negative role in the terminal differentiation of keratinocytes. To understand whether Syk [...] Read more.

Syk is a non-receptor tyrosine kinase involved in the signalling of immunoreceptors and growth factor receptors. Previously, we reported that Syk mediates epidermal growth factor receptor (EGFR) signalling and plays a negative role in the terminal differentiation of keratinocytes. To understand whether Syk is a potential therapeutic target of cancer cells, we further elucidated the role of Syk in disease progression of squamous cell carcinoma (SCC), which is highly associated with EGFR overactivation, and determined the combined effects of Syk and PARP1 inhibitors on SCC viability. We found that pharmacological inhibition of Syk could attenuate the EGF-induced phosphorylation of EGFR, JNK, p38 MAPK, STAT1, and STAT3 in A431, CAL27 and SAS cells. In addition, EGF could induce a Syk-dependent IL-8 gene and protein expression in SCC. Confocal microscopic data demonstrated the ability of the Syk inhibitor to change the subcellular distribution patterns of EGFR after EGF treatment in A431 and SAS cells. Moreover, according to Kaplan-Meier survival curve analysis, higher Syk expression is correlated with poorer patient survival rate and prognosis. Notably, both Syk and EGFR inhibitors could induce PARP activation, and synergistic cytotoxic actions were observed in SCC cells upon the combined treatment of the PARP1 inhibitor olaparib with Syk or the EGFR inhibitor. Collectively, we reported Syk as an important signalling molecule downstream of EGFR that plays crucial roles in SCC development. Combining Syk and PARP inhibition may represent an alternative therapeutic strategy for treating SCC. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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17 pages, 6801 KiB

Open AccessArticle

TDP1 and TOP1 Modulation in Olaparib-Resistant Cancer Determines the Efficacy of Subsequent Chemotherapy

by Jin Won Kim, Ahrum Min, Seock-Ah Im, Hyemin Jang, Yu Jin Kim, Hee-Jun Kim, Kyung-Hun Lee, Tae-Yong Kim, Keun Wook Lee, Do-Youn Oh, Jee-Hyun Kim and Yung-Jue Bang

Cancers 2020, 12(2), 334; https://doi.org/10.3390/cancers12020334 - 3 Feb 2020

Cited by 6 | Viewed by 4135

Abstract

The aim of this study was to elucidate the carryover effect of olaparib to subsequent chemotherapy and its underlying mechanisms. We generated olaparib-resistant SNU-484, SNU-601, SNU-668, and KATO-III gastric cancer cell lines and confirmed their resistance by cell viability and colony forming assays. [...] Read more.

The aim of this study was to elucidate the carryover effect of olaparib to subsequent chemotherapy and its underlying mechanisms. We generated olaparib-resistant SNU-484, SNU-601, SNU-668, and KATO-III gastric cancer cell lines and confirmed their resistance by cell viability and colony forming assays. Notably, olaparib-resistant cell lines displayed cross-resistance to cisplatin except for KATO-III. Inversely, olaparib-resistant SNU-484, SNU-668, and KATO-III were more sensitive to irinotecan than their parental cells. However, sensitivity to paclitaxel remained unaltered. There were compensatory changes in the ATM/ATR axis and p-Chk1/2 protein expression. ERCC1 was also induced in olaparib-resistant SNU-484, SNU-601, and SNU-668, which showed cross-resistance to cisplatin. Olaparib-resistant cells showed tyrosyl-DNA phosphodiesterase 1 (TDP1) downregulation with higher topoisomerase 1 (TOP1) activity, which is a target of irinotecan. These changes of TOP1 and TDP1 in olaparib-resistant cells was confirmed as the underlying mechanism for increased irinotecan sensitivity through manipulated gene expression of TOP1 and TDP1 by specific plasmid transfection and siRNA. The patient-derived xenograft model established from the patient who acquired resistance to olaparib with BRCA2 mutation showed increased sensitivity in irinotecan. In conclusion, the carryover effects of olaparib to improve antitumor effect of subsequent irinotecan were demonstrated. These effects should be considered when determining the subsequent therapy with olaparib. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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29 pages, 6018 KiB

Open AccessArticle

PARP1 Inhibition Augments UVB-Mediated Mitochondrial Changes—Implications for UV-Induced DNA Repair and Photocarcinogenesis

by Csaba Hegedűs, Gábor Boros, Eszter Fidrus, Gréta Nikoletta Kis, Miklós Antal, Tamás Juhász, Eszter Anna Janka, Laura Jankó, György Paragh, Gabriella Emri, Péter Bai and Éva Remenyik

Cancers 2020, 12(1), 5; https://doi.org/10.3390/cancers12010005 - 18 Dec 2019

Cited by 30 | Viewed by 5742

Abstract

Keratinocytes provide the first line of defense of the human body against carcinogenic ultraviolet (UV) radiation. Acute and chronic UVB-mediated cellular responses were widely studied. However, little is known about the role of mitochondrial regulation in UVB-induced DNA damage. Here, we show that [...] Read more.

Keratinocytes provide the first line of defense of the human body against carcinogenic ultraviolet (UV) radiation. Acute and chronic UVB-mediated cellular responses were widely studied. However, little is known about the role of mitochondrial regulation in UVB-induced DNA damage. Here, we show that poly (ADP-ribose) polymerase 1 (PARP1) and ataxia-telangiectasia-mutated (ATM) kinase, two tumor suppressors, are important regulators in mitochondrial alterations induced by UVB. Our study demonstrates that PARP inhibition by ABT-888 upon UVB treatment exacerbated cyclobutane pyrimidine dimers (CPD) accumulation, cell cycle block and cell death and reduced cell proliferation in premalignant skin keratinocytes. Furthermore, in human keratinocytes UVB enhanced oxidative phosphorylation (OXPHOS) and autophagy which were further induced upon PARP inhibition. Immunoblot analysis showed that these cellular responses to PARP inhibition upon UVB irradiation strongly alter the phosphorylation level of ATM, adenosine monophosphate-activated kinase (AMPK), p53, protein kinase B (AKT), and mammalian target of rapamycin (mTOR) proteins. Furthermore, chemical inhibition of ATM led to significant reduction in AMPK, p53, AKT, and mTOR activation suggesting the central role of ATM in the UVB-mediated mitochondrial changes. Our results suggest a possible link between UVB-induced DNA damage and metabolic adaptations of mitochondria and reveal the OXPHOS-regulating role of autophagy which is dependent on key metabolic and DNA damage regulators downstream of PARP1 and ATM. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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19 pages, 5512 KiB

Open AccessArticle

CAF-1 Subunits Levels Suggest Combined Treatments with PARP-Inhibitors and Ionizing Radiation in Advanced HNSCC

by Francesco Morra, Francesco Merolla, Ida Picardi, Daniela Russo, Gennaro Ilardi, Silvia Varricchio, Federica Liotti, Roberto Pacelli, Luca Palazzo, Massimo Mascolo, Angela Celetti and Stefania Staibano

Cancers 2019, 11(10), 1582; https://doi.org/10.3390/cancers11101582 - 17 Oct 2019

Cited by 11 | Viewed by 3575

Abstract

Oral (OSCC) and oropharyngeal (OPSCC) squamous cell carcinomas show high morbidity and mortality rates. We aimed to investigate the role of the “Chromatin Assembly Factor-1” (CAF-1) p60 and p150 subunits, involved in DNA repair and replication, in OSCC and OPSCC progression and in [...] Read more.

Oral (OSCC) and oropharyngeal (OPSCC) squamous cell carcinomas show high morbidity and mortality rates. We aimed to investigate the role of the “Chromatin Assembly Factor-1” (CAF-1) p60 and p150 subunits, involved in DNA repair and replication, in OSCC and OPSCC progression and in response to Poly(ADP-ribose) polymerase (PARP)-inhibitors and exposure to ionizing radiation (IR). We immunostained tissue microarrays (TMAs), including 112 OSCC and 42 OPSCC, with anti-CAF-1/p60 and anti-CAF-1/p150 specific antibodies, correlating their expression with prognosis. Moreover, we assessed the sensitivity to PARP inhibitors and the double-strand breaks repair proficiency by cell viability and HR reporter assays, respectively, in HPV-positive and HPV-negative cell lines upon CAF-1/p60 and CAF-1/p150 depletion. The immunohistochemical analysis revealed a significant prognostic value of both tissue biomarkers combined expression in OSCC but not in OPSCC. In in vitro studies, the p60/150 CAF-1 subunits’ depletion impaired the proficiency of Homologous Recombination DNA damage repair, inducing sensitivity to the PARP-inhibitors, able to sensitize both the cell lines to IR. These results indicate that regardless of the prognostic meaning of p60/p150 tissue expression, the pharmacological depletion of CAF-1 complex’s function, combined to PARP-inhibitors and/or IR treatment, could represent a valid therapeutic strategy for squamous cell carcinomas of head and neck region. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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18 pages, 1516 KiB

Open AccessArticle

PARP1 Co-Regulates EP300–BRG1-Dependent Transcription of Genes Involved in Breast Cancer Cell Proliferation and DNA Repair

by Maciej Sobczak, Andrew R. Pitt, Corinne M. Spickett and Agnieszka Robaszkiewicz

Cancers 2019, 11(10), 1539; https://doi.org/10.3390/cancers11101539 - 11 Oct 2019

Cited by 24 | Viewed by 4847

Abstract

BRG1, an active subunit of the SWI/SNF chromatin-remodeling complex, enables the EP300-dependent transcription of proliferation and DNA repair genes from their E2F/CpG-driven promoters in breast cancer cells. In the current study, we show that BRG1–EP300 complexes are accompanied by poly-ADP-ribose polymerase 1 (PARP1), [...] Read more.

BRG1, an active subunit of the SWI/SNF chromatin-remodeling complex, enables the EP300-dependent transcription of proliferation and DNA repair genes from their E2F/CpG-driven promoters in breast cancer cells. In the current study, we show that BRG1–EP300 complexes are accompanied by poly-ADP-ribose polymerase 1 (PARP1), which emerges as the functional component of the promoter-bound multiprotein units that are capable of controlling gene expression. This enzyme is co-distributed with BRG1 at highly acetylated promoters of genes such as CDK4, LIG1, or NEIL3, which are responsible for cancer cell growth and the removal of DNA damage. ADP-ribosylation is necessary to maintain active transcription, since it ensures an open chromatin structure that allows high acetylation and low histone density. PARP1-mediated modification of BRG1 and EP300 does not affect the association of enzymes with gene promoters; however, it does activate EP300, which acetylates nucleosomes, leading to their eviction by BRG1, thus allowing mRNA synthesis. Although PARP1 was found at BRG1 positive/H3K27ac negative promoters of highly expressed genes in a transformed breast cancer cell line, its transcriptional activity was limited to genes simultaneously controlled by BRG1 and EP300, indicating that the ADP-ribosylation of EP300 plays a dominant role in the regulation of BRG1–EP300-driven transcription. In conclusion, PARP1 directs the transcription of some proliferation and DNA repair genes in breast cancer cells by the ADP-ribosylation of EP300, thereby causing its activation and marking nucleosomes for displacement by BRG1. PARP1 in rapidly dividing cells facilitates the expression of genes that confer a cancer cell phenotype. Our study shows a new mechanism that links PARP1 with the removal of DNA damage in breast cancer cells via the regulation of BRG1–EP300-dependent transcription of genes involved in DNA repair pathways. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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18 pages, 3354 KiB

Open AccessArticle

Cytotoxicity and Differentiating Effect of the Poly(ADP-Ribose) Polymerase Inhibitor Olaparib in Myelodysplastic Syndromes

by Isabella Faraoni, Maria Irno Consalvo, Francesca Aloisio, Emiliano Fabiani, Manuela Giansanti, Francesca Di Cristino, Giulia Falconi, Lucio Tentori, Ambra Di Veroli, Paola Curzi, Luca Maurillo, Pasquale Niscola, Francesco Lo-Coco, Grazia Graziani and Maria Teresa Voso

Cancers 2019, 11(9), 1373; https://doi.org/10.3390/cancers11091373 - 16 Sep 2019

Cited by 14 | Viewed by 3741

Abstract

Myelodysplastic syndromes (MDS) are highly heterogeneous myeloid diseases, characterized by frequent genetic/chromosomal aberrations. Olaparib is a potent, orally bioavailable poly(ADP-ribose) polymerase 1 (PARP1) inhibitor with acceptable toxicity profile, designed as targeted therapy for DNA repair defective tumors. Here, we investigated olaparib activity in [...] Read more.

Myelodysplastic syndromes (MDS) are highly heterogeneous myeloid diseases, characterized by frequent genetic/chromosomal aberrations. Olaparib is a potent, orally bioavailable poly(ADP-ribose) polymerase 1 (PARP1) inhibitor with acceptable toxicity profile, designed as targeted therapy for DNA repair defective tumors. Here, we investigated olaparib activity in primary cultures of bone marrow mononuclear cells collected from patients with MDS (n = 28). A single treatment with olaparib induced cytotoxic effects in most samples, with median IC₅₀ of 5.4 µM (2.0–24.8 µM), lower than plasma peak concentration reached in vivo. In addition, olaparib induced DNA damage as shown by a high proportion of γH2AX positive cells in samples with low IC₅₀s. Olaparib preferentially killed myeloid cells causing a significant reduction of blasts and promyelocytes, paralleled by an increase in metamyelocytes and mature granulocytes while sparing lymphocytes that are not part of the MDS clone. Consistently, flow cytometry analysis revealed a decrease of CD117+/CD123+ immature progenitors (p < 0.001) and induction of CD11b+/CD16+ (p < 0.001) and CD10+/CD15+ (p < 0.01) neutrophils. Morphological and immunophenotypic changes were associated with a dose-dependent increase of PU.1 and CEBPA transcription factors, which are drivers of granulocytic and monocytic differentiation. Moreover, the combination of olaparib with decitabine resulted in augmented cytotoxic and differentiating effects. Our data suggest that olaparib may have therapeutic potential in MDS patients. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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Review

Jump to: Editorial, Research

21 pages, 520 KiB

Open AccessReview

The Nucleolus and PARP1 in Cancer Biology

by Marina Engbrecht and Aswin Mangerich

Cancers 2020, 12(7), 1813; https://doi.org/10.3390/cancers12071813 - 6 Jul 2020

Cited by 39 | Viewed by 6060

Abstract

The nucleolus has been known for a long time to fulfill crucial functions in ribosome biogenesis, of which cancer cells can become addicted to in order to produce sufficient amounts of proteins for cell proliferation. Recently, the nucleolus has emerged as a central [...] Read more.

The nucleolus has been known for a long time to fulfill crucial functions in ribosome biogenesis, of which cancer cells can become addicted to in order to produce sufficient amounts of proteins for cell proliferation. Recently, the nucleolus has emerged as a central regulatory hub in many other cancer-relevant processes, including stress sensing, DNA damage response, cell cycle control, and proteostasis. This fostered the idea that nucleolar processes can be exploited in cancer therapy. Interestingly, a significant proportion of poly(ADP-ribose) polymerase 1 (PARP1) molecules are localized in the nucleolus and PARP1 also plays crucial roles in many processes that are important in cancer biology, including genome maintenance, replication, transcription, and chromatin remodeling. Furthermore, during the last years, PARP1 came into focus in oncology since it represents a promising target of pharmacological PARP inhibitors in various types of cancers. Here, we provide an overview of our current understanding on the role of PARP1 in nucleolar functions and discuss potential implications in cancer biology and therapy. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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15 pages, 3774 KiB

Open AccessReview

The Modified Phenanthridine PJ34 Unveils an Exclusive Cell-Death Mechanism in Human Cancer Cells

by Malka Cohen-Armon

Cancers 2020, 12(6), 1628; https://doi.org/10.3390/cancers12061628 - 19 Jun 2020

Cited by 6 | Viewed by 6452

Abstract

This overview summarizes recent data disclosing the efficacy of the PARP inhibitor PJ34 in exclusive eradication of a variety of human cancer cells without impairing healthy proliferating cells. Its cytotoxic activity in cancer cells is attributed to the insertion of specific un-repairable anomalies [...] Read more.

This overview summarizes recent data disclosing the efficacy of the PARP inhibitor PJ34 in exclusive eradication of a variety of human cancer cells without impairing healthy proliferating cells. Its cytotoxic activity in cancer cells is attributed to the insertion of specific un-repairable anomalies in the structure of their mitotic spindle, leading to mitotic catastrophe cell death. This mechanism paves the way to a new concept of cancer therapy. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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28 pages, 1261 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Combined PARP Inhibition and Immune Checkpoint Therapy in Solid Tumors

by Florent Peyraud and Antoine Italiano

Cancers 2020, 12(6), 1502; https://doi.org/10.3390/cancers12061502 - 9 Jun 2020

Cited by 144 | Viewed by 8999

Abstract

Genomic instability is a hallmark of cancer related to DNA damage response (DDR) deficiencies, offering vulnerabilities for targeted treatment. Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) interfere with the efficient repair of DNA damage, particularly in tumors with existing defects in DNA repair, and [...] Read more.

Genomic instability is a hallmark of cancer related to DNA damage response (DDR) deficiencies, offering vulnerabilities for targeted treatment. Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) interfere with the efficient repair of DNA damage, particularly in tumors with existing defects in DNA repair, and induce synthetic lethality. PARPi are active across a range of tumor types harboring BRCA mutations and also BRCA-negative cancers, such as ovarian, breast or prostate cancers with homologous recombination deficiencies (HRD). Depending on immune contexture, immune checkpoint inhibitors (ICIs), such as anti-PD1/PD-L1 and anti-CTLA-4, elicit potent antitumor effects and have been approved in various cancers types. Although major breakthroughs have been performed with either PARPi or ICIs alone in multiple cancers, primary or acquired resistance often leads to tumor escape. PARPi-mediated unrepaired DNA damages modulate the tumor immune microenvironment by a range of molecular and cellular mechanisms, such as increasing genomic instability, immune pathway activation, and PD-L1 expression on cancer cells, which might promote responsiveness to ICIs. In this context, PARPi and ICIs represent a rational combination. In this review, we summarize the basic and translational biology supporting the combined strategy. We also detail preclinical results and early data of ongoing clinical trials indicating the synergistic effect of PARPi and ICIs. Moreover, we discuss the limitations and the future direction of the combination. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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22 pages, 2839 KiB

Open AccessReview

Therapeutic Strategies and Biomarkers to Modulate PARP Activity for Targeted Cancer Therapy

by Naveen Singh, S. Louise Pay, Snehal B. Bhandare, Udhaya Arimpur and Edward A. Motea

Cancers 2020, 12(4), 972; https://doi.org/10.3390/cancers12040972 - 14 Apr 2020

Cited by 14 | Viewed by 5915

Abstract

Poly-(ADP-ribose) polymerase 1 (PARP1) is commonly known for its vital role in DNA damage response and repair. However, its enzymatic activity has been linked to a plethora of physiological and pathophysiological transactions ranging from cellular proliferation, survival and death. For instance, malignancies with [...] Read more.

Poly-(ADP-ribose) polymerase 1 (PARP1) is commonly known for its vital role in DNA damage response and repair. However, its enzymatic activity has been linked to a plethora of physiological and pathophysiological transactions ranging from cellular proliferation, survival and death. For instance, malignancies with BRCA1/2 mutations heavily rely on PARP activity for survival. Thus, the use of PARP inhibitors is a well-established intervention in these types of tumors. However, recent studies indicate that the therapeutic potential of attenuating PARP1 activity in recalcitrant tumors, especially where PARP1 is aberrantly overexpressed and hyperactivated, may extend its therapeutic utility in wider cancer types beyond BRCA-deficiency. Here, we discuss treatment strategies to expand the tumor-selective therapeutic application of PARP inhibitors and novel approaches with predictive biomarkers to perturb NAD⁺ levels and hyperPARylation that inactivate PARP in recalcitrant tumors. We also provide an overview of genetic alterations that transform non-BRCA mutant cancers to a state of “BRCAness” as potential biomarkers for synthetic lethality with PARP inhibitors. Finally, we discuss a paradigm shift for the use of novel PARP inhibitors outside of cancer treatment, where it has the potential to rescue normal cells from severe oxidative damage during ischemia-reperfusion injury induced by surgery and radiotherapy. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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26 pages, 3953 KiB

Open AccessReview

The Multifactorial Role of PARP-1 in Tumor Microenvironment

by Juan Manuel Martí, Mónica Fernández-Cortés, Santiago Serrano-Sáenz, Esteban Zamudio-Martinez, Daniel Delgado-Bellido, Angel Garcia-Diaz and Francisco Javier Oliver

Cancers 2020, 12(3), 739; https://doi.org/10.3390/cancers12030739 - 20 Mar 2020

Cited by 33 | Viewed by 5798

Abstract

Poly(ADP-ribose) polymerases (PARPs), represent a family of 17 proteins implicated in a variety of cell functions; some of them possess the enzymatic ability to synthesize and attach poly (ADP-ribose) (also known as PAR) to different protein substrates by a post-translational modification; PARPs are [...] Read more.

Poly(ADP-ribose) polymerases (PARPs), represent a family of 17 proteins implicated in a variety of cell functions; some of them possess the enzymatic ability to synthesize and attach poly (ADP-ribose) (also known as PAR) to different protein substrates by a post-translational modification; PARPs are key components in the cellular response to stress with consequences for different physiological and pathological events, especially during neoplasia. In recent years, using PARP inhibitors as antitumor agents has raised new challenges in understanding their role in tumor biology. Notably, the function of PARPs and PAR in the dynamic of tumor microenvironment is only starting to be understood. In this review, we summarized the conclusions arising from recent studies on the interaction between PARPs, PAR and key features of tumor microenvironment such as hypoxia, autophagy, tumor initiating cells, angiogenesis and cancer-associated immune response. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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13 pages, 1601 KiB

Open AccessEditor’s ChoiceReview

ATM-Deficient Cancers Provide New Opportunities for Precision Oncology

by Nicholas R. Jette, Mehul Kumar, Suraj Radhamani, Greydon Arthur, Siddhartha Goutam, Steven Yip, Michael Kolinsky, Gareth J. Williams, Pinaki Bose and Susan P. Lees-Miller

Cancers 2020, 12(3), 687; https://doi.org/10.3390/cancers12030687 - 14 Mar 2020

Cited by 77 | Viewed by 8300

Abstract

Poly-ADP ribose polymerase (PARP) inhibitors are currently used in the treatment of several cancers carrying mutations in the breast and ovarian cancer susceptibility genes BRCA1 and BRCA2, with many more potential applications under study and in clinical trials. Here, we discuss the [...] Read more.

Poly-ADP ribose polymerase (PARP) inhibitors are currently used in the treatment of several cancers carrying mutations in the breast and ovarian cancer susceptibility genes BRCA1 and BRCA2, with many more potential applications under study and in clinical trials. Here, we discuss the potential for extending PARP inhibitor therapies to tumours with deficiencies in the DNA damage-activated protein kinase, Ataxia-Telangiectasia Mutated (ATM). We highlight our recent findings that PARP inhibition alone is cytostatic but not cytotoxic in ATM-deficient cancer cells and that the combination of a PARP inhibitor with an ATR (ATM, Rad3-related) inhibitor is required to induce cell death. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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17 pages, 1528 KiB

Open AccessReview

The Controversial Roles of ADP-Ribosyl Hydrolases MACROD1, MACROD2 and TARG1 in Carcinogenesis

by Karla L.H. Feijs, Christopher D.O. Cooper and Roko Žaja

Cancers 2020, 12(3), 604; https://doi.org/10.3390/cancers12030604 - 5 Mar 2020

Cited by 18 | Viewed by 4344

Abstract

Post-translational modifications (PTM) of proteins are crucial for fine-tuning a cell’s response to both intracellular and extracellular cues. ADP-ribosylation is a PTM, which occurs in two flavours: modification of a target with multiple ADP-ribose moieties (poly(ADP-ribosyl)ation or PARylation) or with only one unit [...] Read more.

Post-translational modifications (PTM) of proteins are crucial for fine-tuning a cell’s response to both intracellular and extracellular cues. ADP-ribosylation is a PTM, which occurs in two flavours: modification of a target with multiple ADP-ribose moieties (poly(ADP-ribosyl)ation or PARylation) or with only one unit (MARylation), which are added by the different enzymes of the PARP family (also known as the ARTD family). PARylation has been relatively well-studied, particularly in the DNA damage response. This has resulted in the development of PARP inhibitors such as olaparib, which are increasingly employed in cancer chemotherapeutic approaches. Despite the fact that the majority of PARP enzymes catalyse MARylation, MARylation is not as well understood as PARylation. MARylation is a dynamic process: the enzymes reversing intracellular MARylation of acidic amino acids (MACROD1, MACROD2, and TARG1) were discovered in 2013. Since then, however, little information has been published about their physiological function. MACROD1, MACROD2, and TARG1 have a ‘macrodomain’ harbouring the catalytic site, but no other domains have been identified. Despite the lack of information regarding their cellular roles, there are a number of studies linking them to cancer. However, some of these publications oppose each other, some rely on poorly-characterised antibodies, or on aberrant localisation of overexpressed rather than native protein. In this review, we critically assess the available literature on a role for the hydrolases in cancer and find that, currently, there is limited evidence for a role for MACROD1, MACROD2, or TARG1 in tumorigenesis. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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18 pages, 1738 KiB

Open AccessReview

The Development of Rucaparib/Rubraca®: A Story of the Synergy Between Science and Serendipity

by Nicola J Curtin

Cancers 2020, 12(3), 564; https://doi.org/10.3390/cancers12030564 - 29 Feb 2020

Cited by 14 | Viewed by 4742

Abstract

The poly(ADP-ribose) polymerase (PARP) inhibitor, Rubraca®, was given its first accelerated approval for BRCA-mutated ovarian cancer by the FDA at the end of 2016, and further approval by the FDA, EMA and NICE followed. Scientists at Newcastle University initiated the early stages, and [...] Read more.

The poly(ADP-ribose) polymerase (PARP) inhibitor, Rubraca®, was given its first accelerated approval for BRCA-mutated ovarian cancer by the FDA at the end of 2016, and further approval by the FDA, EMA and NICE followed. Scientists at Newcastle University initiated the early stages, and several collaborations with scientists in academia and the pharmaceutical industry enabled its final development to the approval stage. Although originally considered as a chemo- or radiosensitiser, its current application is as a single agent exploiting tumour-specific defects in DNA repair. As well as involving intellectual and physical effort, there have been a series of fortuitous occurrences and coincidences of timing that ensured its success. This review describes the history of the relationship between science and serendipity that brought us to the current position. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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20 pages, 1146 KiB

Open AccessReview

Role of Akt Activation in PARP Inhibitor Resistance in Cancer

by Ferenc Gallyas, Jr., Balazs Sumegi and Csaba Szabo

Cancers 2020, 12(3), 532; https://doi.org/10.3390/cancers12030532 - 25 Feb 2020

Cited by 55 | Viewed by 7467

Abstract

Poly(ADP-ribose) polymerase (PARP) inhibitors have recently been introduced in the therapy of several types of cancers not responding to conventional treatments. However, de novo and acquired PARP inhibitor resistance is a significant limiting factor in the clinical therapy, and the underlying mechanisms are [...] Read more.

Poly(ADP-ribose) polymerase (PARP) inhibitors have recently been introduced in the therapy of several types of cancers not responding to conventional treatments. However, de novo and acquired PARP inhibitor resistance is a significant limiting factor in the clinical therapy, and the underlying mechanisms are not fully understood. Activity of the cytoprotective phosphatidylinositol-3 kinase (PI3K)-Akt pathway is often increased in human cancer that could result from mutation, expressional change, or amplification of upstream growth-related factor signaling elements or elements of the Akt pathway itself. However, PARP-inhibitor-induced activation of the cytoprotective PI3K-Akt pathway is overlooked, although it likely contributes to the development of PARP inhibitor resistance. Here, we briefly summarize the biological role of the PI3K-Akt pathway. Next, we overview the significance of the PARP-Akt interplay in shock, inflammation, cardiac and cerebral reperfusion, and cancer. We also discuss a recently discovered molecular mechanism that explains how PARP inhibition induces Akt activation and may account for apoptosis resistance and mitochondrial protection in oxidative stress and in cancer. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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13 pages, 632 KiB

Open AccessReview

ARH1 in Health and Disease

by Hiroko Ishiwata-Endo, Jiro Kato, Linda A. Stevens and Joel Moss

Cancers 2020, 12(2), 479; https://doi.org/10.3390/cancers12020479 - 19 Feb 2020

Cited by 7 | Viewed by 3652

Abstract

Arginine-specific mono-adenosine diphosphate (ADP)-ribosylation is a nicotinamide adenine dinucleotide (NAD)⁺-dependent, reversible post-translational modification involving the transfer of an ADP-ribose from NAD⁺ by bacterial toxins and eukaryotic ADP-ribosyltransferases (ARTs) to arginine on an acceptor protein or peptide. ADP-ribosylarginine hydrolase 1 (ARH1) [...] Read more.

Arginine-specific mono-adenosine diphosphate (ADP)-ribosylation is a nicotinamide adenine dinucleotide (NAD)⁺-dependent, reversible post-translational modification involving the transfer of an ADP-ribose from NAD⁺ by bacterial toxins and eukaryotic ADP-ribosyltransferases (ARTs) to arginine on an acceptor protein or peptide. ADP-ribosylarginine hydrolase 1 (ARH1) catalyzes the cleavage of the ADP-ribose-arginine bond, regenerating (arginine)protein. Arginine-specific mono-ADP-ribosylation catalyzed by bacterial toxins was first identified as a mechanism of disease pathogenesis. Cholera toxin ADP-ribosylates and activates the α subunit of Gαs, a guanine nucleotide-binding protein that stimulates adenylyl cyclase activity, increasing cyclic adenosine monophosphate (cAMP), and resulting in fluid and electrolyte loss. Arginine-specific mono-ADP-ribosylation in mammalian cells has potential roles in membrane repair, immunity, and cancer. In mammalian tissues, ARH1 is a cytosolic protein that is ubiquitously expressed. ARH1 deficiency increased tumorigenesis in a gender-specific manner. In the myocardium, in response to cellular injury, an arginine-specific mono-ADP-ribosylation cycle, involving ART1 and ARH1, regulated the level and cellular distribution of ADP-ribosylated tripartite motif-containing protein 72 (TRIM72). Confirmed substrates of ARH1 in vivo are Gαs and TRIM72, however, more than a thousand proteins, ADP-ribosylated on arginine, have been identified by proteomic analysis. This review summarizes the current understanding of the properties of ARH1, e.g., bacterial toxin action, myocardial membrane repair following injury, and tumorigenesis. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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16 pages, 1717 KiB

Open AccessEditor’s ChoiceReview

PARP Inhibitors as Therapeutics: Beyond Modulation of PARylation

by Ahrum Min and Seock-Ah Im

Cancers 2020, 12(2), 394; https://doi.org/10.3390/cancers12020394 - 8 Feb 2020

Cited by 92 | Viewed by 8878

Abstract

Poly (ADP-ribose) polymerase (PARP) 1 is an essential molecule in DNA damage response by sensing DNA damage and docking DNA repair proteins on the damaged DNA site through a type of posttranslational modification, poly (ADP-Ribosyl)ation (PARylation). PARP inhibitors, which inhibit PARylation through competitively [...] Read more.

Poly (ADP-ribose) polymerase (PARP) 1 is an essential molecule in DNA damage response by sensing DNA damage and docking DNA repair proteins on the damaged DNA site through a type of posttranslational modification, poly (ADP-Ribosyl)ation (PARylation). PARP inhibitors, which inhibit PARylation through competitively binding to NAD+ binding site of PARP1 and PARP2, have improved clinical benefits for BRCA mutated tumors, leading to their accelerated clinical application. However, the antitumor activities of PARP inhibitors in clinical development are different, due to PARP trapping activity beyond blocking PARylation reactions. In this review, we comprehensively address the current state of knowledge regarding the mechanisms of action of PARP inhibitors. We will also discuss the different effects of PARP inhibitors in combination with cytotoxic chemotherapeutic agents regarding the mechanism of regulating PARylation. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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18 pages, 1247 KiB

Open AccessReview

Immunomodulatory Roles of PARP-1 and PARP-2: Impact on PARP-Centered Cancer Therapies

by José Yélamos, Lucia Moreno-Lama, Jaime Jimeno and Syed O. Ali

Cancers 2020, 12(2), 392; https://doi.org/10.3390/cancers12020392 - 8 Feb 2020

Cited by 45 | Viewed by 5480

Abstract

Poly(ADP-ribose) polymerase-1 (PARP-1) and PARP-2 are enzymes which post-translationally modify proteins through poly(ADP-ribosyl)ation (PARylation)—the transfer of ADP-ribose chains onto amino acid residues—with a resultant modulation of protein function. Many targets of PARP-1/2-dependent PARylation are involved in the DNA damage response and hence, the [...] Read more.

Poly(ADP-ribose) polymerase-1 (PARP-1) and PARP-2 are enzymes which post-translationally modify proteins through poly(ADP-ribosyl)ation (PARylation)—the transfer of ADP-ribose chains onto amino acid residues—with a resultant modulation of protein function. Many targets of PARP-1/2-dependent PARylation are involved in the DNA damage response and hence, the loss of these proteins disrupts a wide range of biological processes, from DNA repair and epigenetics to telomere and centromere regulation. The central role of these PARPs in DNA metabolism in cancer cells has led to the development of PARP inhibitors as new cancer therapeutics, both as adjuvant treatment potentiating chemo-, radio-, and immuno-therapies and as monotherapy exploiting cancer-specific defects in DNA repair. However, a cancer is not just made up of cancer cells and the tumor microenvironment also includes multiple other cell types, particularly stromal and immune cells. Interactions between these cells—cancerous and non-cancerous—are known to either favor or limit tumorigenesis. In recent years, an important role of PARP-1 and PARP-2 has been demonstrated in different aspects of the immune response, modulating both the innate and adaptive immune system. It is now emerging that PARP-1 and PARP-2 may not only impact cancer cell biology, but also modulate the anti-tumor immune response. Understanding the immunomodulatory roles of PARP-1 and PARP-2 may provide invaluable clues to the rational development of more selective PARP-centered therapies which target both the cancer and its microenvironment. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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18 pages, 2351 KiB

Open AccessReview

PARylation During Transcription: Insights into the Fine-Tuning Mechanism and Regulation

by Zoltán G. Páhi, Barbara N. Borsos, Vasiliki Pantazi, Zsuzsanna Ujfaludi and Tibor Pankotai

Cancers 2020, 12(1), 183; https://doi.org/10.3390/cancers12010183 - 11 Jan 2020

Cited by 21 | Viewed by 5401

Abstract

Transcription is a multistep, tightly regulated process. During transcription initiation, promoter recognition and pre-initiation complex (PIC) formation take place, in which dynamic recruitment or exchange of transcription activators occur. The precise coordination of the recruitment and removal of transcription factors, as well as [...] Read more.

Transcription is a multistep, tightly regulated process. During transcription initiation, promoter recognition and pre-initiation complex (PIC) formation take place, in which dynamic recruitment or exchange of transcription activators occur. The precise coordination of the recruitment and removal of transcription factors, as well as chromatin structural changes, are mediated by post-translational modifications (PTMs). Poly(ADP-ribose) polymerases (PARPs) are key players in this process, since they can modulate DNA-binding activities of specific transcription factors through poly-ADP-ribosylation (PARylation). PARylation can regulate the transcription at three different levels: (1) by directly affecting the recruitment of specific transcription factors, (2) by triggering chromatin structural changes during initiation and as a response to cellular stresses, or (3) by post-transcriptionally modulating the stability and degradation of specific mRNAs. In this review, we principally focus on these steps and summarise the recent findings, demonstrating the mechanisms through which PARylation plays a potential regulatory role during transcription and DNA repair. Full article

(This article belongs to the Special Issue PARPs, PAR and NAD Metabolism and Their Inhibitors in Cancer)

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