Induction of epithelial differentiation and DNA demethylation in hamster malignant oral keratinocyte by ornithine decarboxylase antizyme

The hamster ornithine decarboxylase antizyme (ODC-Az) cDNA was transfected into the hamster malignant oral keratinocyte cell line, HCPC-1, Ectopic exp ression of ODC-Az resulted in the reversion of malignant phenotypes and alt eration of DNA methylation status of CCGG sites. The phenotypes examined in clude ODC enzymatic activity, doubling time, morphological change, anchorag e dependent growth, tumorigenicity in nude mice, induction of epithelial di fferentiation marker protein (involucrin), and change of cell cycle positio n. Comparison of CCGG DNA methylation status of the ODC-Az and control vect or transfectants revealed a significant increase in demethylation of 5-meth yl cytosines (m(5)C) of CCGG sites in the ODC-Az transfectants. Ectopic exp ression of ODC-Az gene in hamster malignant oral keratinocytes led to reduc e ODC activity and the subsequent demethylation of 5-methyl cytosines, pres umably via the ODC/ polyamines/ decarboxylated S-adenosylmethionine (dc-Ado Met) pathways. Our data suggest that ODC-Az shared the same pathway of poly amines/ dc-AdoMet/DNA methyltransferase (DNA MTase), We propose that ODC-Az mediates a novel mechanism in tumor suppression by DNA demethylation and p resumably re-activation of key cellular genes silenced by DNA hypermethylat ion during cancer development.