PARP4 mRNA expression is upregulated by hypomethylation of promoter CpG sites in cisplatin-resistant cell lines. (A) Relative mRNA expression of PARP4 in three human cisplatin-sensitive ovarian cell lines (PA-1, TOV-112D, and A2780) and three human cisplatin-resistant ovarian cell lines (OVCAR-3, OV-90, and SK-OV-3). (B) The DNA methylation status of the PARP4 promoter region was measured using an Illumina HumanMethylation450 BeadChip, which contained 10 CpG sites at position chr13: 25,085,000-25,087,500 (the human GRCh37/hg19 assembly). (C) Each bar denotes the mean β-value of methylation at the corresponding promoter CpG site of PARP4. (D) The DNA methylation status of the CpG site (cg18582260) in three human cisplatin-sensitive ovarian cell lines and three human cisplatin-resistant ovarian cell lines. (E) Three cisplatin-sensitive ovarian cancer cell lines were treated with 5-aza-2’-deoxycytidine. The methylation status at the cg 18582260 CpG site was measured by qMSP. (F) After treatment of 5-aza-2’-deoxycytidine, PARP4 mRNA expression was determined using RT-qPCR. All experiments were carried out in triplicate, and the results are expressed as the mean ± standard deviation (SD). The statistical significance of observed differences was determined using a t-test or Bayesian t-statistic (*P < 0.05; **P < 0.01; ***P < 0.001). M, methylated CpG site; U, unmethylated CpG site; Con, control; Aza, 5-aza-2’-deoxycytidine.