The Influence of Folic Acid Content of Media on TPA-Induced Transformation of JB6 Cells
The influence of folates on carcinogenesis has been studied for many years, but there are still few published data about the effects of folates on carcinogenic events in cells. The JB6 murine epidermal cell line is well developed and characterized as a model of late stage tumor development. Transformation of these cells in the presence of a promoting agent gives rise to new phenotypes that overcome normal growth controls. Anchorage-independent growth is a phenotypic characteristic of transformed cells. The objectives of these studies were: 1) to examine the growth of JB6 mouse epidermal cells cultured in media with variable folate content and 2) to assess the effects of folate content of media on 12-o-tetra-decanoylphorbol-13-acetate (TPA)-induced anchorage-independent growth of JB6 cells. During the growth studies, the cells were cultured for up to twelve days in several media with folate content ranging from 1.8 nM to 3.0 μM. Growth studies showed a positive, dose response relationship between the folate level of the media and cell growth. Before the anchorage-independent assays were performed, to test cell growth in soft agar with and without 5 ng/ml TPA, the cells were cultured in media containing different levels of folates for four passages. The number of colonies at the end of the fourteen-day incubation period was significantly higher (p<0.05) with each ten-fold increase in media folate content. The increase in colony number was especially marked between the cells grown in media containing 230 nM versus 2.3 μM folic acid. Higher folate content of cell culture media facilitated TPA-induced transformation of JB6 mouse epidermal cells. The mechanism responsible for this finding remains to be identified.