*4.4. Measurement of Mitochondria Membrane Potential (*ψ*m)*

Changes in mitochondrial membrane potential were determined using DiOC**<sup>6</sup>** (3,3'-dihexyloxacarbocyanine iodide; Molecular Probes, Eugene, OR). Cells were seeded into 96-well plates (1 × 10**<sup>4</sup>** cells/well), pre-treated with GTX (5 μM) for 8 h, and then treated with PTX (100 nM) for an additional 48 h. Cells were harvested, washed twice with PBS, resuspended in PBS supplemented with DiOC**<sup>6</sup>** (20 nM), incubated in the dark at 37 ◦C for 15 min, and analyzed immediately using a flow cytometer with an FL-1 filter.

#### *4.5. Western Blot Analysis*

Harvested cells were lysed with RIPA buffer (Elpis Biotech, Daejeon, Korea) supplemented with a protease inhibitor cocktail and phosphatase inhibitors (Sigma-Aldrich). Equal amounts of protein (10 μg/sample) determined with a BCA assay kit (Pierce, Rockford, IL, USA) were subsequently loaded onto SDS-PAGE gels. After electrophoresis, the proteins were transferred onto nitrocellulose membranes (Millipore Corp., Billerica, MA, USA). The membranes were blocked with 5% non-fat skim milk and probed with primary antibodies. The expression level of target proteins was determined using a chemiluminescence kit (Advansta Corp., Menlo Park, CA, USA) and an Amersham Imager 600 (GE Healthcare Life Sciences, Little Chalfont, UK). The expression levels of β-actin were used as a control.

#### *4.6. Small Interfering RNA (siRNA) Transfection*

Human TAp63-siRNA (5'-GCA CAC AGA CAA AUG AAU UUU-3'), human DAPK1-siRNA (5'-CAA CTA TGA TGT TAA CCA A-3'), and negative control-siRNA (Cat. No. SN-1001-CFG) were obtained from Bioneer (Daejeon, Korea). Cells were seeded at a density of 1.5 <sup>×</sup> <sup>10</sup><sup>5</sup> per well in a 6-well plate and grown overnight. The cells were then transfected with 200 nM siRNA using Lipofectamine RNAiMAX Reagent (Invitrogen, Carlsbad, CA, USA) as described in the supplier's protocol. The cells were used for further experiments at 48 h after transfection.

#### *4.7. TAp63 Overexpression Using Transient Transfection*

Transient transfection of cultured cells was performed using Lipofectamine 2000 as described in the supplier's instructions. Cells were plated on 6-well culture plates at a density of <sup>2</sup> <sup>×</sup> 105 cells/well and transfected the next day. Typically, 10 ng of construct DNA was transfected with 9 μL of Lipofectamine. The cultured cells were transiently transfected with either a TAp63 expression vector of TAp63 cDNA cloned into pcDNA3.1 (Addgene, Cambridge, MA, USA) or empty vector pcDNA3.1 (Invitrogen). Cells were transfected for 48 h and analyzed by Western blotting.

#### *4.8. Statistical Analysis*

Student's *t*-test and one-way analysis of variance (ANOVA) using SPSS version 24.0 statistical software (IBM Corp., Armonk, NY, USA) were used for all statistical analyses. The data are presented as the mean ± standard deviation (SD). Differences were determined to be statistically significant at *p* < 0.05 and highly significant at *p* < 0.001.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-3397/17/7/412/s1, Figure S1: Establishment of paclitaxel-resistant ovarian cancer cells, Figure S2: Effect of GTX treatment on autophagy and the Bcl-2 family in PTX-resistant ovarian cancer cells.

**Author Contributions:** G.-B.P. carried out all of the experiments and analyses in this study. D.K. contributed to the conception and design of the study and wrote the manuscript. G.-B.P. and D.K. elaborated study design, coordinated the research. J.-Y.J. critically reviewed and revised the manuscript.

**Funding:** This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science and ICT, MIST) (NRF-2018R1C1B6002381) and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2018R1D1A1B07040382).

**Conflicts of Interest:** The authors declare that they have no competing interest.
