Transcriptional Responses to Growth Factor and G Protein‐Coupled Receptors in PC12 Cells

Abstract

Transcriptional responses to growth factor and G protein-coupled receptors were compared in PC12 cells using retroviral luciferase reporters. In cells stably expressing α_1A-adrenergic receptors, norepinephrine activated all five reporters [AP1 (activator protein-1), SRE (serum response element), CRE (cyclic AMP response element), NFκB) (nuclear factor-κB), and NFAT (nuclear factor of activated T cells)], whereas nerve growth factor (NGF) and epidermal growth factor activated only AP1 and SRE. Activation of P2Y2 receptors by UTP did not activate any reporters. Protein kinase C inhibition blocked NFκB activation by norepinephrine, but potentiated CRE. Mitogen-activated protein kinase kinase inhibition blocked AP1 activation by norepinephrine, but also potentiated CRE. p38 mitogen-activated protein kinase inhibition reduced most norepinephrine responses, but not NGF responses. inhibition of Src eliminated SRE responses to norepinephrine and NGF, and reduced all responses except CRE. Phosphatidylinositol 3-kinase inhibitors markedly potentiated CRE activation by norepinephrine, with only small effects on the other responses. Comparison of the three human subtypes showed that the α_1A activated all five reporters, the α_1B showed smaller effects, and the α_1D was ineffective. Cell differentiation caused by norepinephrine, but not NGF, was reduced by all inhibitors studied. These experiments suggest that α_1A-adrenergic receptors activate a wider array of transcriptional responses than do growth factors in PC12 cells. These responses are not linearly related to second messenger production, and different subtypes show different patterns of activation.