1. Introduction
Breast cancer (BC) represents a significant global health challenge and stands as one of the foremost causes of cancer-related deaths among women globally [
1]. In 2022, it was estimated that there were around 2.308 million cases of BC, making it the most common cancer diagnosed worldwide [
2]. Additionally, BC accounted for nearly 665,684 deaths in 2022, underscoring its significant contribution to morbidity and mortality among women [
2]. The high incidence rate, along with the associated mortality, reinforces the necessity for ongoing research into risk factors and genetic predispositions related to BC.
Despite advances in diagnosis and treatment, the molecular mechanisms underlying BC development/progression remain incompletely understood [
2]. Identifying novel genetic and epigenetic markers associated with BC risk and outcomes is essential for improving preventive measurements, early detection, and personalized therapeutic strategies [
3,
4].
MicroRNAs (miRNAs) are a family of “small noncoding RNAs” that modulate gene expression after transcription and are crucial for a variety of biological processes, such as cell proliferation/differentiation and apoptosis [
5]. Aberrant miRNA expression has been involved in the pathogenesis of several cancers, including BC [
6,
7]. The biogenesis of miRNAs is a multi-step process involving several enzymes, with the ribonucleases DROSHA and DICER being two critical components [
8]. DROSHA, as part of the microprocessor complex, cleaves the primary miRNA transcript into precursor miRNA in the nucleus. DICER subsequently converts the precursor miRNA into a double-stranded molecule that includes the mature miRNA guide strand and the passenger strand in the cytoplasm [
9].
The dysregulated expression of DROSHA and DICER has emerged as a critical factor in BC pathogenesis [
10], and their altered expression levels have been reported to impact several stages of BC development and progression [
11]. This dysregulation can affect crucial cellular processes such as cell growth, invasion, metastasis, and apoptosis, all contributing to the BC malignant phenotype [
12]. The intricate interplay between DICER, DROSHA, and miRNAs underscores their significance in BC biology, highlighting them as potential diagnostic and therapeutic targets for managing this disorder [
13].
Genetic variants in the
DROSHA (Gene ID: 29102) and
DICER (Gene ID: 23405) have been investigated for their potential influence on miRNA processing and cancer susceptibility [
14]. “Single-nucleotide polymorphisms (SNPs)” in these genes, such as rs10719 in
DROSHA and rs3742330 in
DICER, have been associated with altered risk and/or survival outcomes in several malignancies, including esophageal, ovarian, and colorectal cancers [
15]. However, these SNPs’ role in BC remains poorly characterized, with limited and inconsistent evidence [
16,
17].
To address this gap, we conducted a case–control study to comprehensively unravel the association of DROSHA rs10719 and DICER rs3742330 polymorphisms with BC risk and clinicopathological characteristics in a sample of Egyptian women. We genotyped both SNPs in paired breast tumor and adjacent non-cancerous tissue samples, as well as in peripheral blood samples from patients with BC and healthy controls. To the best of our knowledge, this is the first study to investigate these SNPs in a BC population and compare the genotype distributions between tumor tissues and matched normal tissues.
Our findings provide new insights into the potential contributions of miRNA processing gene variants to BC susceptibility and clinical outcomes. Understanding these associations could help to identify novel biomarkers for BC risk assessment, ultimately enabling more precise and effective management of this heterogeneous disease.
2. Materials and Methods
2.1. Study Variant Selection, In Silico Analysis, and Literature Review
DROSHA and
DICER genes’ genomic structures and variants were obtained from the “Ensembl Genomic database (
www.ensembl.org)”. After reviewing and sorting the list, the prevalent biallelic variants,
DROSHA rs10719 (A/G) and
DICER rs3742330 (A/G), were identified for further study. The potential regulatory roles of these variants, influenced by their spatial genomic structures and their chromatin loop-mediated interactions with other genes and variants, were sourced from the 3DSNP database and depicted through three-dimensional visualizations showcasing gene interactions, regulatory enhancers, promoters, transcription factors, and conservation metrics (
https://omic.tech/3dsnpv2/) [
18]. The relevant literature was collated from the “GeneCards human gene database (
www.genecards.org)” and the “National Center for Biotechnology Information (NCBI) (
https://www.ncbi.nlm.nih.gov/)”, with all referenced databases last accessed on 30 March 2024.
To ensure a comprehensive understanding of the relationship between DROSHA rs10719 and DICER rs3742330 variants and their implications in various cancers, we conducted a systematic literature review. This review aimed to identify, analyze, and synthesize existing research on the associations of these variants with BC and other malignancies. The literature search used electronic databases, including “PubMed, Scopus, and Web of Science”. Relevant articles were selected based on the following criteria: studies that investigated “DROSHA rs10719” and/or “DICER rs3742330” in the context of cancer, published in peer-reviewed journals, and involving human subjects. The search strategy utilized keywords such as “DROSHA”, “DICER”, “rs10719”, “rs3742330”, and “cancer risk” in various combinations.
2.2. Study Population
A total of 209 female patients with BC were enrolled in the current study after obtaining the ethical approval of the institutional ethical committee (# 5027, 29 September 2022). These included (1) 103 archived paired tumor and adjacent non-tumor formalin-fixed paraffin-embedded (FFPE) tissue samples recruited from the pathology laboratory of Suez Canal University, Ismailia, and AlByan Laboratory in Port Said, Egypt, as well as (2) 106 blood samples of patients with BC obtained at the time of surgery. They had no prior history of radiotherapy or chemotherapy before tumor resection. Another 106 age-matched control blood samples were retrieved from the blood bank. Written consent was obtained from participants before they took part in this study.
2.3. Pathological and Clinical Assessment
A pathologist performed a post-operative pathological assessment of BC tissue specimens to determine the histopathological type, tumor size, grade, and lymph node infiltration. The Elston and Ellis modification of the Scarff–Bloom–Richardson grading system was used to grade the cancer cells, which assigns scores ranging from 1 to 3 to three parameters: tubule formation, nuclear pleomorphism, and mitotic index. Scores of 3–5 indicate well-differentiated cancer cells (grade 1), scores of 6–7 indicate moderately differentiated cancer cells (grade 2), and scores of 8–9 indicate poor or undifferentiated cancer cells (grade 3). Clinical staging was classified according to the “International Union Against Cancer (UICC)” and the “American Joint Committee on Cancer (AJCC) tumor-lymph node-metastasis (TNM)” staging system. Immunohistochemistry analysis was used to evaluate the hormone receptor status “(estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2/neu))” of the tumor tissues. Patients were then classified into four molecular tumor subtypes based on the results of the immunohistochemical analysis: “(1) Luminal A: ER+, PR+, HER2−, (2) Luminal B: ER+, PR+, HER2+, (3) HER2+ subset: ER−, PR−, HER2+, and (4) Basal-like (triple negative): ER−, PR−, HER2−”.
An evaluation of the prognosis of each patient was conducted using the “Nottingham Prognostic Index (NPI)” and “Immunohistochemical Prognostic Index (IHPI)” [
19]. The NPI was based on three prognostic factors: (i) tumor size, (ii) histological grade, and (iii) lymph node status; it was grouped into three prognostic classes according to the NPI results—good, moderate, and poor. The IHPI scoring system complemented the NPI and was based on the HER2, ER, and PR statuses. Patients were then ranked from 0 to 4 points and divided into three classes—good, moderate, and poor. In addition, the “European Society of Medical Oncology (ESMO)” clinical recommendations for the follow-up of primary BC was used to predict the risk of recurrence and divided into three categories—low, intermediate, and high [
20]. The follow-up of the patients was conducted to assess loco-regional recurrence, disease-free survival, and overall survival.
2.4. Sample Collection
FFPE tissue and blood samples (3 mL) on EDTA-coated vacutainers were collected from patients with BC. FFPE tissue samples included both tumor tissue and adjacent non-tumor tissue. Blood samples were obtained at the time of surgery prior to any treatment. Control blood samples were age-matched to the cases and retrieved from the blood bank.
2.5. Allelic Discrimination Analysis
After genomic DNA isolation using a commercially available DNA extraction kit, “QIAamp DNA Blood Mini kit (Cat. No. 51104, QIAGEN, Hilden, Germany)”, following the procedures outlined by the supplier’s guidelines, measurements to assess the quality/quantity of the isolated genetic material were conducted through “Nanodrop-1000 spectrophotometer (NanoDrop Tech., Wilmington, NC, USA)”. The DNA samples were then carefully preserved at −80 degrees Celsius for subsequent allelic discrimination polymerase chain reaction (PCR) analysis. The rs10719 in DROSHA and rs3742330 in DICER were genotyped using TaqMan SNP genotyping assays on the “StepOne™ Real-Time PCR system” (Applied Biosystems, Foster City, CA, USA). The assays C___7761648_10 and C__27475447_10 with the catalog numbers 4351379 and 4351379, respectively (Applied Biosystems), probed the wild/mutant alleles in the following context sequences: “[VIC/FAM]TATTTTATTTCAATGAGCACACTTC[A/G]TTCATTGTCTGCAGGAAAC AGGC and CTTCAATCTTGTGTAAAGGGATTAG[A/G]CACCCTAACAGAGCAAGA TCCAATA”, respectively; these sequences aligned with the reference genome build GRCh38. The exact formulations and the concentrations of the reagents used in each PCR have been described in prior studies [
21]. PCR was accomplished in a 25 μL volume mixture containing 1× TaqMan Genotyping Master Mix, 1× SNP genotyping assay mix, and 20 ng genomic DNA. The PCR cycling protocol consisted of an initial step at 95 °C for 10 min, followed by 40 cycles comprising 15 s at 95 °C and 1 min at 60 °C [
22]. To mitigate the risk of contamination, no-template controls accompanied each batch of experiments, and to ensure reliability, a subset of the samples, amounting to 10%, was subsequently retested, achieving total agreement with the initial results. The post-amplification analysis was executed using specialized software provided by the PCR system’s manufacturer.
2.6. Statistical Analysis
SNP analysis, including the Hardy–Weinberg equilibrium, allele, and genotype frequencies, was performed using SNPStat (
www.snpstats.net). The Chi-square test was used for comparison. Adjusted odds ratios (ORs) with 95% confidence intervals (CI) were calculated using logistic regression models for multiple genetic association models, adjusting for relevant covariates [
21]. The association of the SNPs with clinical and pathological markers was assessed using Fisher’s exact test for categorical variables and Student’s
t-test for continuous variables. A paired
t-test was applied to compare genotypes between paired tumor and non-tumor tissue samples. Univariate and multivariate logistic regression analyses were performed to estimate the impacts of SNPs on BC risk, calculating ORs and 95% CIs. Survival analyses were not conducted as preliminary assessments yielded insignificant associations between the studied variants and survival outcomes. All statistical analyses were conducted with a two-sided approach, and a
p-value of less than 0.05 was deemed statistically significant. SPSS software version 27.0 (IBM Corporation, Armonk, NY, USA) was applied for statistical analysis.
4. Discussion
In this study, we investigated the association of two common polymorphisms in the miRNA processing genes DROSHA (rs10719) and DICER (rs3742330) with BC risk and clinical outcomes in an Egyptian population. We found that both SNPs were significantly associated with altered BC susceptibility, with the DROSHA rs10719 A allele and the DICER rs3742330 G allele conferring increased risk. Furthermore, a higher frequency of the risk alleles was detected in breast tumor tissues compared to adjacent normal tissues, suggesting a potential role for these variants in driving miRNA dysregulation during breast tumorigenesis. However, neither SNP showed significant associations with clinicopathological characteristics or survival outcomes.
Initially, in our observations regarding the lateralization of BC, there was a predominance of cases (approximately two-thirds of cases) affecting the right side, although they showed insignificant association with the clinicopathological characteristics of the study population (
Table 3,
Table 4 and
Table 5); this may provide additional insights into the biological factors influencing tumorigenesis. This lateralization could reflect anatomical, hormonal, or environmental factors, which may warrant further investigation [
24]. Understanding whether the affected side correlates with specific genetic makeup or tumor biology may enhance our comprehension of BC heterogeneity. Although the predominance of right-sided tumors does not alter our primary findings regarding the associations of the studied variants with BC risk, it suggests an avenue for future research to explore the implications of tumor location concerning genetic predispositions [
25].
DROSHA and
DICER are essential endoribonucleases involved in the biogenesis of microRNAs (miRNAs), which play pivotal roles in regulating gene expression and various cellular processes [
26].
DROSHA processes primary miRNA transcripts (pri-miRNAs) into precursor miRNAs (pre-miRNAs) in the nucleus. The functioning of
DROSHA is vital as it ensures that the remaining pre-miRNA is appropriately sized for subsequent processing by
DICER. Any alterations in
DROSHA activity, such as those potentially conferred by the rs10719 variant, might disrupt this initial step of miRNA maturation, leading to aberrant levels of downstream miRNAs [
27].
DICER, on the other hand, processes pre-miRNAs into mature miRNAs in the cytoplasm and is also involved in the generation of small interfering RNAs (siRNAs) [
28]. The
DICER rs3742330 variant may influence
DICER’s enzymatic efficiency, affecting the quantity and quality of generated mature miRNAs. This disruption can have significant downstream consequences, including the altered expression of target mRNAs involved in critical cellular pathways such as apoptosis, proliferation, and differentiation [
29]. For instance, the dysregulation of miRNAs processed through these pathways can lead to the misregulation of oncogenes and tumor suppressor genes, thereby promoting tumorigenesis. Specific miRNAs that
DROSHA and
DICER can potentially impact include oncogenic miRNAs like miR-21 and tumor suppressor miRNAs such as let-7. Elevated levels of oncogenic miRNAs can facilitate cancer cell proliferation and survival by inhibiting pro-apoptotic signals. Conversely, a deficit in tumor suppressor miRNAs can lead to the inhibition of oncogenes, further driving cancer progression [
30]. Thus, understanding the genetic variants in miRNA processing genes like
DROSHA and
DICER not only provides insights into BC susceptibility but also highlights the importance of downstream miRNA-mediated regulatory networks in the development and progression of BC.
Our findings on the association of
DROSHA rs10719 with increased BC risk align with a previous study by Jiang et al., which reported a higher frequency of the AA genotype in patients with BC compared to healthy controls in a Chinese population [
16]. Also, it has been associated with colorectal and bladder cancers in previous reports [
31,
32]. Similarly, the association of the
DICER rs3742330 G allele with cancer risk has been observed in several other malignancies, including colorectal [
31,
33], gastric [
34,
35], hepatocellular [
36], prostate [
37], larynx [
38], and thyroid [
39] cancers, as well as precancerous cervical lesion [
40].
The functional consequences of these SNPs for miRNA processing efficiency and target gene regulation remain to be fully elucidated. However, it has been proposed that the rs10719 variant may affect
DROSHA’s mRNA stability and alter its subcellular localization [
41]. Interestingly, this SNP is located in the miR-27b binding site within
DROSHA 3′UTR [
42], which has been proven to be oncogenic in MCF7 BC cells and may have tumor suppressive activity under certain conditions, as evidenced by a “CRISPR/Cas9 deletion study” conducted by Hannafon et al. [
43]. At the same time, the rs3742330 variant may influence
DICER mRNA expression and enzymatic activity [
42]. As this SNP is located within the potential target sequences of miR-632, miR-3622a-5p, and miR-5582-5p, it may affect cellular processes like apoptosis, cell growth, and migration/invasion [
44]. Mir-632 was found to be a putative epigenetic down-regulator of DNAJB6, a constitutive member of the heat shock protein 40 family, which supports BC oncogenesis and progression [
45]. MiR-3622b-5p has been reported to impact the Her2-positive BC cell line negatively, and miR-5582-5p, via the long noncoding RNA LUCAT1/miR-5582-3p/TCF7L2 axis, was associated with the regulatory mechanisms of BC stemness [
46]. The
DICER rs3742330 G variant enhances the affinity of these microRNAs for the DICER 3′ UTR, reducing DICER expression. This decrease results in diminished RNA cleavage and translation repression, along with heightened cell migration, invasion, and angiogenesis, all of which may impact the progression of BC [
47]. This could support the present study findings that carrying the G allele and the GG genotype confer higher susceptibility to developing BC in our cohort.
The higher frequency of risk alleles in tumor tissues than matched normal tissues suggests that the studied variants may undergo positive selection during BC development, potentially conferring a growth advantage to tumor cells. This finding is consistent with the concept of “onco-miRNAs”, whereby dysregulated miRNA networks can promote various hallmarks of cancer, such as sustained proliferation, the evasion of apoptosis, and metastatic dissemination [
48]. However, it is essential to note that the observed differences in genotype frequencies between tumor and normal tissues could also be influenced by factors such as tumor purity, genetic heterogeneity, and tissue-specific mosaicism [
49,
50,
51,
52].
The lack of significant associations between the studied SNPs and clinicopathological features or survival outcomes in our cohort suggests that these variants may primarily influence BC initiation rather than progression [
52,
53,
54]. However, it is also possible that the impacts of these SNPs on clinical outcomes may be modulated by other genetic, epigenetic, or environmental factors not accounted for in our analysis [
55,
56]. Additionally, the relatively small sample size and short follow-up duration of our study may have limited our ability to detect subtle associations with survival endpoints.
Our study has several strengths, including the comprehensive evaluation of both blood and tissue samples, including age-matched healthy controls, and the detailed clinicopathological annotation of BC cases. However, we acknowledge certain limitations that should be considered when interpreting our results. First, our study was conducted in a single institution and may not fully represent the Egyptian population. Second, we did not have information on potential confounding factors such as lifestyle habits and environmental exposures, which could have influenced the observed associations. Third, we did not perform functional experiments to validate the biological consequences of the studied SNPs on miRNA processing efficiency or target gene expression.