Mechanism of activation of protein kinase D2(PKD2) by the CCKB/gastrin receptor

Recently, we cloned a novel serine/threonine kinase termed protein kinase D2 (PKD2). PKD2 can be activated by phorbol esters both in vivo and in vitro but also by gastrin via the cholecystokinin/CCKB receptor in human gastric cancer cells stably transfected with the CCKB/gastrin receptor (AGS-B cells). Here we identify the mechanisms of gastrin-induced PKD2 activation in AGS-B cells. PKD2 phosphorylation in response to gastrin was rapid, reaching a maximum after 10 min of incubation. Our data demonstrate that gastrin-stimulated PKD2 activation involves a heterotrimeric Galpha(q) protein as well as the activation of phospholipase C. Furthermore, we show that PKD2 can be activated by classical and novel members of the protein kinase C (PKC) family such as PKCalpha, PKCepsilon, and PKCeta. These PKCs are activated by gastrin in AGS-B cells. Thus, PKD2 is likely to be a novel downstream target of specific PKCs upon the stimulation of AGS-B cells with gastrin. Our data suggest a two-step mechanism of activation of PKD2 via endogenously produced diacylglycerol and the activation of PKCs.