Stimulation of RNA synthesis in rat parotid lobules by phorbol myristate acetate.

Incubation of parotid lobules with phorbol 12-myristate 13-acetate (PMA) transiently stimulated the incorporation of [3H]uridine into RNA. At 100 nM PMA, the rate of RNA synthesis during the first hour was 30% above control rates. The Ca2+ ionophore A23187 had no effect on either basal or PMA-stimulated RNA synthesis. Stimulation by 100 nM PMA was reversed by the protein kinase C inhibitor staurosporin (10 nM). When PMA was added together with isoproterenol or okadaic acid, both of which are potent activators of RNA synthesis, the increase in RNA synthesis was additive rather than synergistic. The results suggest that in the rat parotid gland, protein kinase C induces the rapid transcription of certain cellular genes by a mechanism that is independent of the beta-adrenergic receptor-activated pathway.