THE GASTRIN-RELEASING PEPTIDE RECEPTOR IS RAPIDLY PHOSPHORYLATED BY AKINASE OTHER THAN PROTEIN-KINASE-C AFTER EXPOSURE TO AGONIST

Several guanine nucleotide-binding protein-coupled receptors are known to be rapidly phosphorylated after agonist exposure. In this study we show that the gastrin-releasing peptide receptor (GRP-R) is rapidly p hosphorylated in response to agonist exposure. When [P-32]orthophospha te-labeled cells were exposed to bombesin, the receptor was maximally phosphorylated on serine and threonine residues within 1 min. Although addition of 12-O-tetradecanoylphorbol 13-acetate also resulted in pho sphorylation of the GRP-R, elimination of protein kinase C activity us ing the inhibitor 7-hydroxystaurosporine did not prevent bombesin-indu ced GRP-R phosphorylation. We conclude that a kinase other than protei n kinase C is principally responsible for the rapid, agonist-induced p hosphorylation of the GRP-R.