Signalling pathway leading to an activation of mitogen-activated protein kinase by stimulating M-3 muscarinic receptor

Abstract

The signalling pathway leading to an activation of mitogenactivated protein (MAP) kinase subtypes Erk-1 and -2 upon stimulation of muscarinic receptor with carbachol in human neuroblastoma SK-N-BE2(C) cells was investigated. Carbachol activated Erk-1/-2 by stimulating M-3 muscarinic receptor, as determined by specific antagonists for individual muscarinic receptors. The activation of Erk-1/-2 by carbachol was blocked by the inhibition or down-regulation of protein kinase C (PKC). Among the multiple PKC isoforms expressed in SK-N-BE2(C) cells, only PKC epsilon was activated by the treatment of carbachol, and selective down-regulation of PKC epsilon was sufficient to block Erk-l/-2 activation. Carbachol treatment induced activation of the serine/threonine protein kinase Raf, and an inhibition of Raf blocked Erk-1/-2 activation. Ectopic expression of inhibitory small GTPase Ras, RasN17, blocked the carbachol-induced Raf activation without affecting the activation of PKC epsilon, while the inhibition of PKC blocked the Raf activation. Thus, these results suggest that carbachol-induced activation of PKC epsilon mediates Erk 1/-2 activation by a sequential activation of Ras, Raf and MAP kinase kinase.