ABSTRACT
Stimulation of phosphoinositide-hydrolysing phospholipase C (PLC) generating inositol-1,4,5-trisphosphate is a major calcium signalling pathway used by a wide variety of membrane receptors, activating distinct PLC-beta or PLC-gamma isoforms. Here we report a new PLC and calcium signalling pathway that is triggered by cyclic AMP (cAMP) and mediated by a small GTPase of the Rap family. Activation of the adenylyl cyclase-coupled beta2-adrenoceptor expressed in HEK-293 cells or the endogenous receptor for prostaglandin E1 in N1E-115 neuroblastoma cells induced calcium mobilization and PLC stimulation, seemingly caused by cAMP formation, but was independent of protein kinase A (PKA). We provide evidence that these receptor responses are mediated by a Rap GTPase, specifically Rap2B, activated by a guanine-nucleotide-exchange factor (Epac) regulated by cAMP, and involve the recently identified PLC-epsilon isoform.
