Homologous desensitization of HEL cell thrombin receptors. Distinguishable roles for proteolysis and phosphorylation.

摘要: Loss of sensitivity to thrombin following an initial response is characteristic a number cell types, including platelets. It has recently been proposed that receptors resemble other G protein-coupled receptors, but activation involves novel mechanism in which cleaves the receptor, exposing new N terminus serves as ligand for receptor. Based upon this model, we have examined receptor desensitization by comparing effects with those peptide corresponding N-terminal sequence proteolysis thrombin: SFLLRNPNDKYEPF or TRP42/55. Like thrombin, TRP42/55 stimulated pertussis toxin-sensitive inositol 1,4,5-trisphosphate formation, raised cytosolic Ca2+, and inhibited cAMP formation megakaryoblastic HEL line. Exposure either desensitized cells both, not third agonist, neuropeptide Y. The rate recovery after depended order agonist addition. Resensitization brief exposure required up 24 h could be cycloheximide. TRP42/55, on hand, was detectable within 30 min serine/threonine phosphatase inhibitors, responsiveness also observed addition phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). However, while protein kinase inhibitor staurosporine completely prevented caused TPA, it had only limited effect These results demonstrate protein-mediated can reproduced receptor-derived suggest occurs at least two mechanisms. first, seen requires synthesis recovery. second, well phosphorylation, possibly itself. Although protien C activated presumably responsible does appear play major role This suggests kinases, such inactivate adrenergic rhodopsin, are involved down-regulation function.