Data from ΔDNMT3B Variants Regulate DNA Methylation in a Promoter-Specific Manner

DNA methyltransferase 3B (DNMT3B) is critical in de novo DNA methylation during development and tumorigenesis. We recently reported the identification of a DNMT3B subfamily, ΔDNMT3B, which contains at least seven variants, resulting from alternative pre-mRNA splicing. ΔDNMT3Bs are the predominant expression forms of DNMT3B in human lung cancer. A strong correlation was observed between the promoter methylation of RASSF1A gene but not p16 gene (both frequently inactivated by promoter methylation in lung cancer) and expression of ΔDNMT3B4 in primary lung cancer, suggesting a role of ΔDNMT3B in regulating promoter-specific methylation of common tumor suppressor genes in tumorigenesis. In this report, we provide first experimental evidence showing a direct involvement of ΔDNMT3B4 in regulating RASSF1A promoter methylation in human lung cancer cells. Knockdown of ΔDNMT3B4 expression by small interfering RNA resulted in a rapid demethylation of RASSF1A promoter and reexpression of RASSF1A mRNA but had no effect on p16 promoter in the lung cancer cells. Conversely, normal bronchial epithelial cells with stably transfected ΔDNMT3B4 gained an increased DNA methylation in RASSF1A promoter but not p16 promoter. We conclude that promoter DNA methylation can be differentially regulated and ΔDNMT3Bs are involved in regulation of such promoter-specific de novo DNA methylation. [Cancer Res 2007;67(22):10647–52]