Differential coupling of α1-, α2-, and β-adrenergic receptors to mitogen-activated protein kinase pathways and differentiation in transfected PC12 cells

Three adrenergic receptor families that selectively activate three different G proteins (alpha(1)/G(q/11), alpha(2)/G(i), and beta/G(s)) were used to study mitogen-activated protein kinase (MAPK) activation and differentiation in PC12 cells. PC12 cells were stably transfected with alpha(1a)-, alpha(2A)-, or beta(1)-adrenerse receptors (ARs) in an inducible expression vector, and subclones were characterized. Norepinephrine stimulated inositol phosphate formation in alpha(1A)-transfected cells, inhibited cyclic adenosine 3'5'-monophosphate (cAMP) formation in alpha(1A)-transfected cells, and stimulated cAMP formation in beta(1)-transfected cells. Nerve growth factor activated extracellular signal-regulated kinases (ERKs) in all cell lines; however, norepinephrine activated ERKs only in alpha(1A)- and beta(1)-transfected cells but not in alpha(2A)-transfected cells. Norepinephrine also activated c-Jun NH2-terminal kinase and p38 MAPK in alpha(1A)-transfected cells but not in beta(1)- or alpha(2A)-transfected cells. Norepinephrine caused differentiation of PC12 cells expressing alpha(1A)-ARs but not those expressing beta(1)- or alpha(2A)-ARs. However, norepinephrine acted synergitically with nerve growth factor in promoting differentiation of cells expressing beta(1)-ARs. Whereas ERKs are activated by G(i)- but not G(s)-linked receptors in many fibroblastic cell lines, we observed the opposite in PC12 cells. The results show that activation of the different G protein signaling pathways has different effects on MAPKs and differentiation in PC12 cells, with G(q) signaling pathways activating all three major MAPK pathways.