REGULATION OF THE DNA METHYLTRANSFERASE BY THE RAS-AP-1 SIGNALING PATHWAY

Using deletion analysis and site-specific mutagenesis to map the 5' regulatory region of the DNA methyltransferase (MeTase) gene, we show that a 106-bp sequence (at -1744 to -1650) bearing three AP-1 sites is responsible for induction of DNA MeTase promoter activity. Using transient cotransfection chloramphenicol acetyltransferase assays in P19 cells, we show that the DNA MeTase promoter is induced by c-Jun or Ha-Ras but not by a dominant negative mutant of Jun, partial derivative 9. The activation of the DNA MeTase promoter by Jun is inhibited in a ligand dependent manner by the glucocorticoid receptor, Stable expression of Ha-Ras in P19 cells results in induction of transcription of the DNA MeTase mRNA as determined by nuclear run on assays and the steady state levels of DNA MeTase mRNA as determined by an RNase protection assay. These experiments establish a potential molecular link between nodal cellular signaling pathways and the control of expression of the DNA MeTase gene. This provides us with a possible molecular explanation for the hyperactivation of DNA MeTase in many cancer cells and suggests that DNA MeTase is one possible downstream effector of Ras.