Metabotropic signaling cascade involved in α4β2 nicotinic acetylcholine receptor-mediated PKCβII activation

Nicotinic acetylcholine receptors (nAChRs) belong to the ionophore receptor family, which regulates plasma membrane conductance to Na+, K+, and Ca2+ ions. Some studies, however, have shown that nAChRs also employ second messengers for intracellular signaling. We previously showed that alpha 4 beta 2 nAChR mediates the translocation of protein kinase C beta II (PKC beta II) from the cytoplasm to the plasma membrane, which is a typical activation marker for PKC beta II. In this study, we investigated the molecular mechanisms underlying PKC beta II activation through alpha 4 beta 2 nAChR. alpha 4 beta 2 nAChR is the most abundant nAChR subtype and is implicated in various brain functions and diseases. Putative alpha 4 beta 2 nAChR signaling components were identified by knockdown or chemical inhibition of candidate proteins, and the signaling cascade was deduced by protein interactions in predicted cellular components. alpha 4 beta 2 nAChR-mediated PKC beta II translocation was found to occur in an ionophore activity-independent manner. Nicotinic stimulation of alpha 4 beta 2 nAChR activated Src in a beta-arrestin1 and 14-3-3 eta-dependent manner. Activated Src phosphorylated the tyrosine residue(s) on Syk molecules, which in turn interacted with phospholipase C gamma 1 to trigger the translocation of PKC beta II to the cell membrane by elevating cellular diacylglycerol levels. The activated PKC beta II in turn exerted a positive feedback effect on Src activation, suggesting that beta 4 beta 2 nAChR signaling is amplified by a positive feedback loop. These findings provide novel information for unveiling the previously unclear metabotropic second messenger-based signal transduction pathway of nAChRs.