Addition of gastrin or cholecystokinin octapeptide (CCK-8) to cultures of Rat-1 cells stably transfected with the CCK2 (CCKB/gastrin) receptor induced protein kinase D (PKD) activation that was detectable within 1 min and reached a maximum (∼10-fold) after 2.5 min of hormonal stimulation. Half-maximal PKD activation for both CCK-8 and gastrin was achieved at 10 nM. Treatment with various concentrations of the selective PKC inhibitors Ro 31-8220 or GF-I potently blocked PKD activation induced by subsequent addition of CCK-8 in a concentration-dependent fashion. Our results indicate that PKC-dependent PKD activation is a novel early event in the action of gastrin and CCK-8 via CCK2 receptors.
