c-fos regulation in untransformed as compared to transformed Balb/c 3T3 fibroblasts.

The regulation of c-fos expression was studied in the untransformed A31 Balb/c 3T3 mouse fibroblast cell line and in the derivative benzo(a)pyrene (BPA31), dimethylbenz(a)anthracene (DA31) and the Kirsten sarcoma virus (KA31) transformed cell lines. The peak induced c-fos RNA levels varied by about 20-fold among the cell lines. Differences in the peak level of c-fos RNA were due primarily to differences in the de novo transcriptional rate rather than in the stability of the message. Superinduction of 6-12x occurred after combined cycloheximide and phorbol ester treatment in the 4 cell lines. Superinduction of 20x in the untransformed A31 cells but only 1-3x in the transformed cells occurred when cycloheximidine and 10% serum were used. Superinduction of 5x in the A31 cells and of 1-2x in the transformed cells was found using cycloheximide and A23187. The data suggest the possibility that a labile protein which degrades the c-fos RNA is stabilized or increased in the transformed cells.