• Sat. Jan 22nd, 2022

The present data do not allow us to distinguish between these not mutually exclusive possibilities

Byacusticavisual

Jan 3, 2022

The present data do not allow us to distinguish between these not mutually exclusive possibilities. A particularly interesting finding was that despite the fact that okadaic acid increased 1b-AR phosphorylation, neither the [Ca2+]i increase nor the production of [3H]inositol trisphosphate induced by noradrenaline were significantly altered. the direct activation of protein kinase?C by phorbol myristate acetate. and Shih (Pitcher (Ricciarelli & Azzi, 1998). The present data do not allow us to distinguish between these not mutually exclusive possibilities. A particularly interesting finding was that despite the fact that okadaic acid increased 1b-AR phosphorylation, neither the [Ca2+]i increase nor the production of [3H]inositol trisphosphate induced by noradrenaline were significantly altered. This is in marked contrast with the results obtained with PMA, which greatly reduced both receptor responses. We have previously observed that bradykinin induced 1b-AR phosphorylation without leading to adrenoceptor desensitization (Medina em et al /em ., 1998); however, bradykinin induced only a 50% increase in receptor phosphorylation. Okadaic acid induced an increase in 1b-AR phosphorylation of similar magnitude as PMA but the functional repercussions markedly differ. The results on noradrenaline-stimulated [35S]GTPS binding indicate that the phosphorylation induced by the treatment with okadaic acid does indeed impair the adrenoceptor-G protein coupling, but to a much lesser extent than PMA or noradrenaline. Such okadaic acid-induced decrease of receptor-G protein coupling does not however seem to affect the adrenergic actions in whole cells, i.e. the intracellular calcium and inositol trisphosphate responses were not decreased. The differences in the effect of PMA and okadaic acid on the receptor response may also reflect the fact that in addition to receptor phosphorylation other event may underlie desensitization. Among these, PKC-dependent phosphorylation of other molecular entities participating in signalling, such as G protein(s) or SETDB2 phospholipase?C might result in desensitization. The actions of both PMA and okadaic acid on 1b-AR phosphorylation seem to involve PKC activity, but they had very different functional repercussions. This suggests that differences may exist in the sites phosphorylated under the action of PMA or okadaic acid. One possibility that may explain this puzzle is that PMA may activate PKC isoforms that are not active in the basal state or in the presence of okadaic acid. PKC is a multigene family of protein kinase with different sensitivity to activators and substrate selectivity (Newton, 1995). MM-589 TFA There is no data on the isoforms of PKC that participate in 1b-AR phosphorylation. As indicated, the sites involved in PKC-mediated 1b-AR phosphorylation have been identified in the carboxyl terminus (Ser394 and Ser400) although a third, MM-589 TFA yet unidentified, site seems to exist (Diviani em et al /em ., 1997). The sites where basal phosphorylation takes place and the kinase(s) involved have not yet been positively identified. The functional significance of such basal phosphorylation is unknown. In summary, our data indicate that inhibition of protein phosphatases MM-589 TFA increase 1b-AR phosphorylation. This effect seems to involve PKC activity. In contrast to the effect of PMA, okadaic acid does not block 1b-adrenergic actions in whole cells and only marginally affect receptor coupling MM-589 TFA to G proteins as evidenced by the noradrenaline-stimulated [35S]GTPS binding. Acknowledgments This research was partially supported by Grants from DGAPA (IN 200596 and IN 205199), CONACyT (27569-N) and Fundacin Miguel Alemn. Abbreviations 1-AR1-adrenoceptor[Ca2+]iintracellular calciumDMEMDulbecco’s modified Eagle’s mediumGRKG-protein receptor kinasePKCprotein kinase?CPMAphorbol 12-myristate 13-acetate.