Role of ERCCl promoter hypermethylation in drug resistance to cisplatin in human gliomas

Abstract

Overexpression of ERCCl mRNA is associated with drug resistance to cisplatin in human gliomas, but the role of the ERCCl promoter In drug resistance has not been demonstrated. We have used sodium bisulfite sequencing to compare ERCCl promoter methylation patterns in clsplatin-sensitive and cisplatin-resistant glioma cells. The levels of ERCCl DNA methylation, mRNA and protein in 32 human glioma samples were examined by methylation specific PCR, real-time RT-PCR and immunohlstochemlstry, respectively. Meanwhile, cisplatin sensitivities to these human glioma samples were tested by hlstoculture drug response assay. Hypermethylation was observed in the upstream 5Kb region of the ERCCl promoter of cisplatin-sensitive glioma cell lines. ERCCl DNA methylation levels were highly variable in 32 human glioma samples ranging from 0.1 to 0.87, which have shown significant difference between cisplatin-sensitive samples and cisplatin-resistant samples (p < 0.05). The relative expression levels of ERCCl mRNA in 32 glioma samples were also variable from 0.01 to 5.71. No detectable or tow expression of ERCCl protein was shown in 7 glioma samples. ERCCl promoter methylation was inversely correlated to mRNA expression (r =-0.903 p= 0.001) as well as protein expression (r -0.884 p= 0.001). Moreover, ERCCl mRNA expression was significantly associated with protein levels (r = 0.840 p = 0.001). In summary, the aberrant CpG island methylation in ERCCl promoter region exists in human glioma cell lines as well as clinical glioma samples. ERCCl DNA methylation could regulate the expression of downstream mRNA and protein, and was associated with cisplatin chemosensitivity. © 2009 UICC.