Signaling pathways activated by α1-adrenergic receptor subtypes in PC12 cells

PC12 cells were used to compare signaling pathways activated by α1-adrenergic receptor (AR) subtypes. PC12 cells were transfected with human α1A, α1B, or α1D-ARs, and subclones stably expressing receptor densities in physiological ranges isolated and characterized. Norepinephrine (NE) activated a large number of signaling pathways in transfected cells, including inositol phosphate formation, intracellular calcium, all three arms of the mitogen activated protein kinase pathways, and a number of tyrosine kinases. Activation of mitogen activated protein kinase pathways and tyrosine kinases was not blocked by chelation of intracellular calcium with BAPTA or inhibition of protein kinase C. NE also activated luciferase reporter constructs for seven different transcription factors (AP1, SRE, CRE, NFκB, NFAT, Stat, GAS) following transfection into α1A–AR expressing PC12 cells. However, similar increases in inositol phosphate formation and intracellular Ca2+ caused by purinergic P2Y2 receptor activation did not activate any of these reporters. Comparison of α1–AR subtypes showed that the α1A activated all seven reporters, the α1B showed smaller effects, while the α1D was ineffective. NE caused differentiation of α1A, but not α1B or α1D, -AR expressing PC12 cells similar to that caused by NGF. This NE-induced differentiation was reduced or blocked by all inhibitors tested. We conclude that α1-ARs activate many signaling pathways and transcriptional responses in PC12 cells, which are not linearly related to second messenger production, and which may differ for different α1–AR subtypes.