DUSP7 and DUSP8 promoter hypermethylations: Predictors of clinical outcomes in advanced epithelial ovarian carcinoma

Abstract

5501 Background: The Dual specificity phosphatases (DUSPs) are a subclass of the protein tyrosine phosphatase (PTP) gene family which appears to be selective for dephosphorylating the critical phosphothreonine and phosphotyrosine residues within the mitogen-activated protein kinases (MAPKs) leading to inactivation. MAPK activation is a downstream target of several oncogenes and may give rise to oncogenic transformation, and hence DUSPs are potential tumor suppressor genes. The aim of this study was to investigate if DUSPs are subject to methylation-dependent silencing in epithelial ovarian cancer. Methods: In this study, promoter methylation and gene expression of the DUSPs genes (DUSP1, DUSP2, DUSP3, DUSP4, DUSP5, DUSP6, DUSP7, DUSP8 and DUSP10) were investigated in 9 ovarian cancer cell lines and in 74 primary epithelial ovarian tumors (Stage III/IV), using methylation specific PCR (MSP) and Reverse- transcription PCR (RT-PCR). The 74 clinical samples were retrospectively retrieved from a large Phase III RCT (the EORTC 55931/NCIC OV10) with clinical follow-up in excess of 6.5 years. Results: Ovarian Cancer Cell lines: Aberrant CpG methylation detected in DUSP1, DUSP2, DUSP4, DUSP6, DUSP7 and DUSP8. DUSP7 promoter methylation was associated with downregulation of mRNA expression. Primary Ovarian Tumors: Methylation of DUSP1, DUSP2, DUSP7 and DUSP8 was observed in 15–38% of the primary tumors. DUSP7 methylation is a predictor of adverse PFS in both univariate (median PFS 10.6 m versus 13.3m, p=0.002) and multivariate (Cox Regression HR 2.76, p<0.001) analyses, and is associated with a trend for poorer OS (22.1 m versus 29.3 m, p=0.07). In contrast, DUSP8 methylation is an independent predictor of favorable PFS (median 23.7m versus 11.5m; Cox Regression HR 0.30, p=0.006) and OS (HR 0.31, p=0.013). 5-year OS for DUSP8 methylated patients was 58.3% compared with 16.1% for DUSP8 unmethylated (HR 0.277, p=0.005). Conclusion: This is the first report of DUSP methylation in epithelial ovarian cancer. The study suggests that methylation-dependent transcriptional silencing of DUSP7 in advanced epithelial ovarian cancer may represent an independent predictor of adverse PFS. DUSP8 methylation, on the other hand, is a favorable clinical outcome marker. No significant financial relationships to disclose.