Signaling pathways activated by alpha(1)-adrenergic receptor subtypes in PC12 cells

PC12 cells were used to compare signaling pathways activated by alpha (1)-a drenergic receptor (AR) subtypes. PC12 cells were transfected with human al pha (1A), alpha (1B), or alpha (1D)-ARs, and subclones stably expressing re ceptor densities in physiological ranges isolated and characterized. Norepi nephrine (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 o f 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, C RE, NF kappaB,NFAT, Stat, GAS) following transfection into alpha (1A)-AR ex pressing PC12 cells. However, similar increases in inositol phosphate forma tion and intracellular Ca2+ caused by purinergic P2Y2 receptor activation d id not activate any of these reporters. Comparison of alpha (1)-AR subtypes showed that the alpha (1A) activated all seven reporters, the alpha (1B) s howed smaller effects, while the alpha (1D) was ineffective. NE caused diff erentiation of alpha (1A), but not alpha (1B) or alpha (1D),-AR expressing PC12 cells similar to that caused by NCF. This NE-induced differentiation w as reduced or blocked by all inhibitors tested. We conclude that alpha (1)- ARs activate many signaling pathways and transcriptional responses in PC12 cells, which are not linearly related to second messenger production, and w hich may differ for different alpha (1)-AR subtypes. (C) 2001 Elsevier Scie nce Inc. All rights reserved.