Induction of polyomavirus DNA replication by cyclic AMP and a tumor promoter

The effects of reagents that stimulate the intracellular level of cyclic AMP (cAMP), and of a tumor promoter, on polyomavirus (Py) DNA replication were examined in a Py-transformed rat cell line, designated the LPT line. cAMP-stimulating reagents (forskolin and 3-isobutyl-1-methyl xanthine) were found to induce replication of Py DNA in normally growing LPT cells and to enhance replication of the viral DNA in cells exposed to suboptimal doses of UV light and mitomycin C (which have been previously shown to induce Py DNA replication in LPT cells). The tumor promoter 12-O-tetradecanoyl phorbol-13-acetate did not cause a significant induction in Py DNA replication when it was applied to the cells alone, but enhanced replication of the viral DNA when it was applied together with the cAMP-stimulating reagents. Cycloheximide, an inhibitor of protein synthesis, was found to inhibit the induction of Py DNA replication by the cAMP-stimulating reagents. Based on these data, and on previous studies of the Py enhancer, it is proposed that cAMP may induce synthesis of an enhancer-binding protein that causes Py DNA replication in LPT cells by binding and activating an enhancer element which is a component of the Py origin.