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 acetyl-transferase 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, delta 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.