DNA methylation and collagen IV gene expression in F9 teratocarcinoma cells.

Although undifferentiated F9 teratocarcinoma cells express low levels of mRNAs for collagen IV, previous transient transfection experiments using an alpha 1(IV) collagen gene promoter-enhancer-CAT construct revealed a high level of transcriptional activity in these cells. In this report, we find that when this construct is introduced stably into undifferentiated F9 teratocarcinoma cells, expression does not occur unless the cells are treated with retinoic acid and dibutyryl-cAMP. Such activation mimics the endogenous gene activity. Treatment of the cells containing the integrated construct with 5-azacytidine, an agent which prevents DNA methylation, also activates transcription and acts synergistically with retinoic acid and cAMP. Analysis of DNA isolated from F9 teratocarcinoma cells revealed that there was a specific demethylation of the DNA within the 5'-flanking region of the collagen IV genes following treatment with retinoic acid and cAMP. These results suggest that during differentiation, DNA demethylation may play an important role in transcriptional regulation of the collagen IV genes.