Biochemical and immunochemical analysis of avian beta 1 and mammalian beta 2-adrenergic receptors

Regulation of the cAMP signal transduction pathway by protein kinase C in rat submandibular cells

Treatment of rat submandibular acinar cell extracts with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) caused the dose-dependent activation of protein kinase C (PKC), assessed by the phosphorylation of a novel and highly specific substrate. This effect was duplicated by a diacylglycerol, but not by the 4 alpha-phorbol ester 4 alpha-phorbol 12,13-didecanoate. The TPA elevation of PKC was blocked by the PKC inhibitors H-7 and sangivamycin. In intact cells, TPA caused the translocation of PKC from cytosol to membrane, consistent with its known mode of activation. The beta-adrenergic agonist, isoproterenol, stimulated cAMP levels which were significantly reduced by preactivation of PKC. This inhibitory PKC effect was reversed by H-7. When cAMP was stimulated at the post-receptor level, however, by forskolin, NaF or GTP[gamma S], PKC did not inhibit, but rather enhanced the cyclic nucleotide response. Since PKC phosphorylated an endogenous protein of 55 kDa, the size of the beta 1 receptor, these findings indicate that, as in other cell types, PKC can desensitize adenylate cyclase by direct phosphorylation of the beta receptor, but potentiate the cAMP response by a post-receptor mechanism. In mucin secretion studies in the model, TPA alone caused the cAMP-independent release of up to 44% total mucin, which was much less than additive with the isoproterenol response. When the cAMP-mucosecretory response was stimulated at the adenylate cyclase level by forskolin, however, the TPA + forskolin effects were additive. These findings on the modulation of cAMP by PKC indicate cross-talk regulation in the phosphoinositide-cAMP signal transduction pathways in submandibular acinar cells.

A monoclonal antibody directed against the beta 1-adrenergic receptor from turkey erythrocyte membranes

A monoclonal antibody was raised against the affinity purified beta 1-adrenergic receptor from turkey erythrocytes. This antibody, B120, of the IgG1 isotype, precipitates the photoaffinity-labeled purified receptor and the corresponding binding activity. The antibody recognizes the 42 kDa component of the receptor of erythrocyte membranes, after electrotransfer on nitrocellulose. B120 does not inhibit binding of dihydroalprenolol on membranes and has no effect on the activity of adenylate cyclase. Since specific immunofluorescence was detected only after ethanol treatment of the erythrocytes, the epitope recognized by B120 appears not to be accessible at the cell surface.