Sustained Signaling by Phospholipase C-γ Mediates Nerve Growth Factor-Triggered Gene Expression

Abstract

In contrast to conventional signaling by growth factors that requires their continual presence, a 1-min pulse of nerve growth factor (NGF) is sufficient to induce electrical excitability in PC12 cells due to induction of the peripheral nerve type 1 (PN1) sodium channel gene. We have investigated the mechanism for this triggered signaling pathway by NGF in PC12 cells. Mutation of TrkA at key autophosphorylation sites indicates an essential role for the phospholipase C-γ (PLC-γ) binding site, but not the Shc binding site, for NGF-triggered induction of PN1. In concordance with results with Trk mutants, drug-mediated inhibition of PLC-γ activity also blocks PN1 induction by NGF. Examination of the kinetics of TrkA autophosphorylation indicates that triggered signaling does not result from sustained activation and autophosphorylation of the TrkA receptor kinase, whose phosphorylation state declines rapidly after NGF removal. Rather, TrkA triggers an unexpectedly prolonged phosphorylation and activation of PLC-γ signaling that is sustained for up to 2 h. Prevention of the elevation of intracellular Ca²⁺ levels using BAPTA-AM results in a block of PN1 induction by NGF. Sustained signaling by PLC-γ provides a means for differential neuronal gene induction after transient exposure to NGF.

ACKNOWLEDGMENTS

We thank L. Greene for providing the nnr cell line and all derived Trk transfectants, G. Valdez for constructing the pPeripherin clone, and G. Mandel for helpful comments and critical reading of the manuscript.

This work was supported by grants from the National Institutes of Health, NS18218 to S.H. and NS 35148 to R.S.