Muscarinic acetylcholine receptor regulation of ERK and JNK in CHO cells

Extracellular signal-regulated kinases (ERKs) and the c-Jun N-terminal kinases/stress- activated protein kinases (JNKs/SAPKs) are activated by an array of extracellular signals to mediate a variety of cellular responses e.g. mitogenesis, differentiation, hypertrophy and apoptosis. The study investigated the regulation of ERK and JNK by agonist-mediated stimulation of the human m2-AChR or m3-AChR stably expressed in CHO cells. Stimulation of both receptors dramatically activated ERK, although stimulation by the m3-AChR was more sustained. The m3-AChR is efficiently coupled to JNK activation, whereas the m2-AChR is not. Activation of JNK in CHO-m3 cells was delayed and more sustained relative to that of ERK in either CHO-m2 or CHO-m3 cells. The dose-dependence for methacholine (MCh)-stimulated JNK activation by m3-AChR and ERK activation by both receptor subtypes were similar. Although pertussis toxin (PTX) had no effect on Ins(1,4,5)P3 accumulation in CHO-m3 cells, there was significant inhibition of agonist-induced ERK and JNK activation in CHO-m3 cells, suggesting that the m3-AChR was able to couple to Gi/o in addition to Gq. ERK activation was entirely PTX-sensitive in CHO-m2 cells. ERK activation in both cell types was shown to be independent of Ca2+. However, JNK activation by m3 receptors was shown to have both a Ca2+-depdnent and a Ca2+-independent component. PKC inhibition studies demonstrated a novel PKC- and an atypical PKC-component, but not a classical PKC-component in ERK activation in CHO-m2 cells, whereas, there appears to be a cPKC and an aPKC-component in CHO-m3 cells. In contrast to this, PKC appears to have an inhibitory role in m3-AChR-mediated JNK activation. The results presented demonstrate that the m2-AChR activate ERK and JNK via divergent mechanisms.