PLCε Selectively Transduces Thrombin Versus LPA Signals to Astrocyte Proliferation Through Rap1 and Rho

Abstract

Phospholipase C epsilon (PLCε) is a recently discovered PLC that, in contrast to other PLCs, responds directly to inputs from Ras and Rho family small G‐proteins. Using primary astrocytes isolated from a PLCε‐deficient mouse strain we show that endogenous G‐protein coupled receptors for LPA, S1P and thrombin utilize predominantly PLCε for inositol phosphate (InsP) and DAG formation. LPA‐ and S1P‐mediated InsP production was sensitive to Pertussis toxin (65±8% and 74±9% inhibition respectively) whereas the thrombin response was reduced by C3 toxin (68±13% inhibition), suggesting that these ligands activate PLCε through different mechanisms, a Gi pathway for LPA and S1P and a Rho mediated pathway for thrombin. Thrombin stimulated [3H]thymidine incorporation mediated by was markedly reduced in KO astrocytes (66±2%) and further studies revealed that PLCε is required for thrombin‐induced sustained ERK phosphorylation. Activation of a Ras family protein, Rap1, was required for ERK phosphorylation and DNA synthesis and the activation of this small G‐protein was abolished in KO cells. Notably LPA‐induced ERK and mitogenic effects were not Rap1 or PLCε dependent. Thus PLCε is selectively utilized by thrombin vs. LPA to transduce mitogenic signals through mechanism distinct from its role in generation of PLC‐derived second messengers.National Institute of Health Grant GM 36927 and GM 53536.