α7 nAChR-mediated activation of MAP kinase pathways in PC12 cells

Abstract

The α7 nicotinic acetylcholine receptor (α7 nAChR) plays a fundamental role in Ca2+-dependent activation of signaling pathways that can modulate intracellular events involved in learning and memory. Activation of extracellular signal-regulated kinase-1 and -2 (ERK1/2) are well documented Ca2+ signaling events, but these have not been well characterized in response to α7 nAChR-selective ligands. The present study examined activation of ERK1/2 and explored pathways leading to CREB phosphorylation utilizing α7 nAChR-selective ligands in PC12 cells endogenously expressing α7 nAChRs. Robust concentration-dependent increase in ERK1/2 phosphorylation was triggered by structurally diverse α7 nAChR agonists such as nicotine, choline, GTS-21, SSR-180711A and PNU-282987 in the presence of the positive allosteric modulator (PAM) PNU-120596. This effect was attenuated by selective α7 nAChR antagonists or by chelation of extracellular Ca2+. ERK1/2 phosphorylation was also attenuated by inhibitors of calmodulin-dependent protein kinase II (CaMKII), p38 MAP kinase and mitogen-activated protein kinase kinase1/2 (MEK1/2), indicating the involvement of these kinases upstream of ERK1/2. This was confirmed by direct measurement of p38 MAPK and MEK1/2 phosphorylation. These data suggest that α7 nAChR agonist-triggered Ca2+ transient in PC12 cells induces activation of CaMKII, leading to sequential phosphorylation of p38 MAPK, MEK1/2, ERK1/2 and CREB. Such mechanisms may endow the α7 nAChRs with roles in modulating Ca2+-dependent intracellular second messenger events implicated in diverse aspects of cognition.