Multiple effects of phorbol esters on hormone-sensitive adenylate cyclase activity in S49 lymphoma cells

Abstract

In S49 lymphoma cells, 12-O-tetradecanoyl phorbol-13-acetate (TPA) enhances adenylate cyclase activity and doubles cAMP accumulation in response to beta-adrenergic stimulation at 37 degrees C, putatively via the action of protein kinase C. At 27 degrees C, TPA has the opposite effect, inhibiting cAMP production in response to isoproterenol by approximately 25%. TPA also inhibits the response to prostaglandin E1 (PGE1), another stimulant of hormone-sensitive adenylate cyclase in these cells, by 30% at 37 degrees C and almost 50% at 27 degrees C. In contrast, TPA enhances responses to forskolin and cholera toxin at both 27 and 37 degrees C. In membranes from cells treated with TPA, PGE1-stimulated adenylate cyclase activity is inhibited by 50%, whereas the catalytic activity stimulated by NaF or forskolin is enhanced. TPA reduces the potency of both PGE1 and isoproterenol for cAMP generation by 50%. TPA causes a similar decrease in beta-adrenergic agonist affinity with no reduction in the density of either antagonist or agonist binding sites in wild type cells and in cells lacking the alpha-subunit of the stimulatory transducer protein (Gs) (cyc-) or lacking functional receptor Gs coupling (UNC). Therefore, TPA has at least three functionally distinct effects on hormone-sensitive adenylate cyclase in S49 cells: a 50% reduction in agonist affinity, attenuation of receptor-transducer coupling, and enhancement of GTP-dependent catalytic activity. We conclude that multiple and opposing effects of TPA on hormone-sensitive adenylate cyclase occur simultaneously within the same cell, affecting the responses to several agonists differently.(ABSTRACT TRUNCATED AT 250 WORDS)