BOMBESIN GRP STIMULATES A PROTEIN-KINASE IN SWISS 3T3 CELLS THAT PHOSPHORYLATES MICROTUBULE-ASSOCIATED PROTEIN-KINASE

Nerve growth factor (NGF)- and epidermal growth factor (EGF)-stimulated MAP kinase activities from PC-12 cells were recently found to be resolvable into two peaks (microtubule-associated protein [MAP] kinases I and II) by ion-exchange or hydrophobic-interaction HPLC, and both kinases I and II were activated by various growth factors, by okadaic acid, and by phorbol esters. In the present study both MAP kinases I and II were also activated by bombesin/gastrin-releasing peptide (GRP) in Swiss 3T3 cells, and the peak of activation in response to GRP occurred earlier than that observed with EGF. In this work, we confirmed the results reported by Bierman et al. (J. Cell. Phys., 142, 441-448). Since the cDNA for the bombesin/GRP receptor indicates that this receptor has a transmembrane topology like that of other G-protein-coupled receptors, an alternative signal transduction pathway may mediate the activation of MAP kinase by bombesin/GRP.