CHARACTERISTICS OF PROTOONCOGENE EXPRESSION IN A5-CELLS

Stimulation of beta-adrenergic receptors by isoproterenol or addition of 8-BrcAMP rapidly and transiently induces the expression of the prot ooncogenes, c-fos, and jun B, but not that of c-jun in A5 cells. These results indicate that different intracellular pathways may operate wi thin the same cell for the induction of this group of early response g enes. The inducibility of c-fos and jun B genes by either isoprotereno l of 8-BrcAMP is transcriptionally regulated and accompanied by increa ses in their respective products. Furthermore, both c-fos and jun B mR NA levels are elevated at G0/G1 phase of the A5 cell cycle and are ind ucible by isoproterenol or 8-BrcAMP at the different phases of the cel l cycle. These data further suggest a possible role of c-fos and jun B in A5 cell cycle.