The candidate tumor suppressor gene, RASSF1A, from human chromosome 3p21.3is involved in kidney tumorigenesis

Clear cell-type renal cell carcinomas (clear RCC) are characterized almost universally by loss of heterozygosity on chromosome 30, which usually invol ves any combination of three regions: 3p25-p26 (harboring the VHL gene), 3p 12-p14.2 (containing the FHIT gene), and 3p21-p22, implying inactivation of the resident tumor-suppressor genes (TSGs). For the 3p21-p22 region, the a ffected TSGs remain, at present, unknown. Recently, the RAS association fam ily 1 gene (isoform RASSF1A), located at 3p21.3, has been identified as a c andidate lung and breast TSC. In this report, we demonstrate aberrant silen cing by hypermethylation of RASSF1A in both VHL-caused clear RCC tumors and clear RCC without VHL inactivation. We found hypermethylation of RASSF1A's CC-rich putative promoter region in most of analyzed samples, including 39 of 43 primary tumors (91%). The promoter was methylated partially or compl etely in all 18 RCC cell lines analyzed. Methylation of the CC-rich putativ e RASSF1A promoter region and loss of transcription of the corresponding mR NA were related causally. RASSF1A expression was reactivated after treatmen t with 5-aza-2 ' -deoxycytidine. Forced expression of RASSF1A transcripts i n KRC/Y, a renal carcinoma cell line containing a normal and expressed VHL gene, suppressed growth on plastic dishes and anchorage-independent colony formation in soft agar. Mutant RASSF1A had reduced growth suppression activ ity significantly. These data suggest that RASSF1A is the candidate renal T SG gene for the 3p21.3 region.