Relationship Between the Inactivation of Dusp9 Expression and Hypermethylation of the Gene Promoter in Renal-Cell Carcinoma

Abstract

DUSP9 / MKP-4 belongs to a subclass of bispecific protein phosphatases, which, by dephosphorylation of MAP kinases (ERK1 / 2, p38 and JNK), negatively regulate the activity of MAP kinase cascades. Hyperactivation of MAP kinase cascades is observed in many different cancer types, including kidney cancer. We have previously found that in human clear cell renal cell carcinoma (ccRCC) DUSP9 is downregulated. In this study, using the semi-quantitative RT-PCR method, we evaluated the expression level of DUSP9 in tumors of patients with different stages of renal cell carcinoma of three histological variants: ccRCC (26 samples), papillary (2 samples) and chromophobic (1 sample). For each tumor 3 distantly located pieces were analyzed. We showed that DUSP9 mRNA level was significantly reduced in all three pieces of each tumor compared with normal tissue. Promoter hypermethylation may be one mechanism of gene repression in cancer. Using the DNA demethylating agent 5-Aza-2'-deoxycytidine and RCC cell lines we showed a correlation between the mRNA level and methylation level of the promoter region of DUSP9 gene. We then analyzed methylation level of DUSP9 promoter in 31 clinical samples of RCC (11 female and 20 male patients). It was increased in 10 out of 11 female RCC. In men, the methylated alleles of DUSP9 were not detected in either tumor or paired normal specimens. The results of our study indicate that DUSP9 transcriptional repression is an early event in kidney carcinogenesis and that DUSP9 expression in RCC can be regulated epigenetically via DNA methylation of the gene promoter, in a sex-related manner. They also indicate the existence of alternative mechanisms of inactivation of the DUSP9 gene in RCC.