Protein kinase C phosphorylates the inhibitory guanine‐nucleotide‐binding regulatory component and apparently suppresses its function in hormonal inhibition of adenylate cyclase

Abstract

Human platelet membrane proteins were phosphorylated by exogenous, partially purified Ca2 +-activated phospholipid-dependent protein kinase (protein kinase C). The phosphorylation of one of the major substrates for protein kinase C (Mr = 41000) was specifically suppressed by the fl subunit of the inhibitory guaninenucleotide-binding regulatory component (Gi, Ni) of adenylate cyclase. The free a subunit of Gi ( M , = 41 000) also served as an excellent substrate for the kinase (> 0.5 mol phosphate incorporated per mol of subunit), but the Gi oligomer (a . fl. y) did not. Treatment of cyc-S49 lymphoma cells, which are deficient in GJNS (the stimulatory component) but contain functional Gi/Ni, with the phorbol ester, 12-0-tetradecanoylphorbol 13-acetate, a potent activator of protein kinase C, did not alter stimulation of adenylate cyclase catalytic activity by forskolin, whereas the Gi/Ni-mediated inhibition of the cyclase by the hormone, somatostatin, was impaired in these membranes. The results suggest that the a subunit of the inhibitory guanine-nucleotide-binding regulatory component of adenylate cyclase may be a physiological substrate for protein kinase C and that the function of the component in transducing inhibitory hormonal signals to adenylate cyclase is altered by its phosphorylation.

Phorbol‐ester‐induced phosphorylation of the β2‐adrenergic receptor decreases its coupling to Gs

“…In contrast, the same treatment in cells expressing PKC "/32AR did not reduce the proportion of receptor in the high affinity state, It is generally accepted that the proportion of receptor in the guanine-nucleotidesensitive high-affinity state for its agonist represents the ability of the receptor to couple to (3s [34]. These results The results presented here also sulilest that the PMAinduced increase in the efficacy of adenylyl cyclase stimulation by isoproterenoi is independent of' the receptor phosphorylation, Most tikely, this morons© results from the phosphorylation of other components of the signalling pathway [16][17][18], which in turn leads to the increase in basal and forskolin.stimulated activities, In this respect, it is noteworthy that PMA induces very similar increases in basal and stimulated adenylyl cyclas¢ activities (basal: 2.4.fold, isoproterenolstimulated: 2.9.reid, t'orskolin-stimulated: 1,9-fold; Table I). …”

“…However, the effects of PKC-mediated phosphorylation on the adenylyl cyclase reactivity appear to be rather complex, and both desensitization [10][11][12][13][14][15] and supersensitization [4][5][6][7][8][9] have been reportecl following phorbol-ester treatments, In many mammalian cell lines, hormone-, fluorideand GTP.stimulated adenylyl cyclase activities have been shown to be enhanced by phorbol-ester treatment [4][5][6][7][8][9]. Phosphorylation by PKC of the inhibitory GTPbinding protein (G~) [16,17] and of the adenylyl cyclase catalytic unit itself [18,19] have been proposed to contribute to this sensitization effect of the phorbol-esters.…”

“…The PMA treatment increases the efficacy of both forskolin and isoproterenol to stimulate the adenylyl cyclase, most likely via the PKCmediated phosphorylation of the adenylyl cyclase and/or Gi [16][17][18]. In contrast, the phosphorylation of the /3zAR by PKC results in a reduced ability of the receptor to couple to Gs,…”

Regulation of type V adenylyl cyclase by PMA‐sensitive and ‐insensitive protein kinase C isoenzymes in intact cells

“…However, the direction and degree of this alteration have been variable among studies [1]. Investigators have tried to explain this variability by the different sites of interaction; PKC may phosphorylate multiple components within the cAMP signaling system, such as receptors, G proteins and AC [2][3][4][5].…”

The PKC inhibitor, bisindolymaleimide, blocks DOI's attenuation of the effects of 8-OH-DPAT on female rat lordosis behavior

“…The 5-HT 1A receptor contains multiple putative phosphorylation sites for both PKC and cAMP dependent protein kinase (PKA) [33] and both kinases can lead to desensitization of 5-HT 1A receptors [12,34]. In addition, G iα proteins may be subject to phosphorylation, leading to attenuation of 5-HT 1A receptor signaling [15,20]. Thus multiple opportunities exist for cross talk between 5-HT 1A and 5-HT 2 receptors and there is substantial evidence for their functional interaction [7,21,26].…”