Silencing of the mouse H-rev107 gene encoding a class II tumor suppressor by CpG methylation.

H-rev107 is a tumor suppressor originally isolated in revertants of H-ras-transformed cell lines. The gene is ubiquitously expressed in normal tissues but down-regulated in primary carcinomas or in many cell lines derived from tumors, including WEHI 7.1 lymphoma cells. Here, we show that unlike in H-rev107-expressing cells or tissues the 5'-end of H-rev107 containing a CpG-rich region of 421 bp is highly methylated in WEHI 7.1 lymphoma cells, correlating with silencing of this gene. Repression of H-rev107 transcription in these cells could be relieved by chemically induced hypomethylation with 5-aza-dC. In addition, upon in vitro methylation, expression of the luciferase reporter gene driven by the H-rev107 promoter decreased by 80% in WEHI 7.1 and 293 cells. Furthermore, co-transfection of the methyl-CpG binding proteins, MeCP2 and MBD2, inhibited H-rev107 promoter activity up to 70% in SL2 cells when the promoter was methylated. By chromatin immunoprecipitation assays, we observed in vivo binding of MeCP2 and MBD2 to the 5'-end of H-rev107 in WEHI 7.1 cells, which was reduced to undetectable levels upon 5-aza-dC treatment, concluding that MeCP2 and MBD2 might be involved in silencing the methylated H-rev107 gene in lymphoma cells and probably certain tumors.