G protein-coupled receptor regulation of CREB and the processing of the amyloid precursor protein
Human SH-SY5Y neuroblastoma cells were used to investigate mechanisms involved in phosphorylation of the transcription factor CREB (cAMP response-element binding-protein) after activation of two endogenously expressed Gq/11 -protein-coupled receptors, the M3 muscarinic acetylcholine (mACh) B2 bradykinin receptors. Stimulation with either methacholine (MCh) or bradykinin resulted in maximal increases in CREB phosphorylation within 1 min, with either a rapid subsequent decrease (bradykinin) to basal levels, or a maintained plateau response (MCh). Inhibitor studies were performed to assess the involvement of a number of potential kinases in signalling to CREB phosphorylation. Removal of extracellular Ca2+, inhibition of Ca2+/calmodulin-dependent protein kinases (CaMKs) and down-regulation of protein kinase C (PKC), resulted in reduced CREB phosphorylation after M3 mACh and B2 bradykinin receptor activation. Inhibition of MEK1/2 (MAPK/ERK kinase) by U0126 resulted in significantly reduced CREB phosphorylation levels after B2 bradykinin but not M3 mACh receptor activation. It has also been demonstrated that maintained phosphorylation of CREB is necessary for cAMP response element (CRE)-dependent gene transcription as the M3 mACh, but not the B2 bradykinin receptor activates both a recombinant CRE-dependent reporter gene, and endogenous c-Fos gene transcription.;Activation of the M3 mACh receptor is capable of increasing the processing of the amyloid precursor protein (APP) via an alpha-secretase pathway to yield the non-amyloidogenic secreted protein, sAPPalpha. This increase in sAPPalpha was shown to be dependent upon influx of Ca 2+ from the extracellular milieu. Inhibition of CaMKs and PKC resulted in reduced secretion of sAPPalpha, demonstrating a role for these kinases in M3 mACh receptor regulation of APP processing.