The Cholinergic Stimulating Effects of Ciliary Neurotrophic Factor and Leukemia Inhibitory Factor Are Mediated by Protein Kinase C

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Abstract
The intracellular mechanisms through which two trophic factors, ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF), regulate cholinergic development were examined in sympathetic neuron cultures. Treatment with CNTF or LIF increased levels of choline acetyltransferase (ChAT) activity by 375 and 350%, respectively. However, in neuronal cultures depleted of protein kinase C (PKC) activity by chronic phorbol ester treatment, neither CNTF nor LIF elevated ChAT activity. Further, the stimulation of ChAT due to increased cell density was not observed in PKC‐depleted sympathetic neurons. The inhibition of CNTF‐stimulated ChAT by phorbol ester occurred in a dose‐dependent manner and chronic phorbol ester treatments did not alter the levels of the catecholamine biosynthetic enzyme tyrosine hydroxylase. Moreover, increased levels of diacylglycerol, an endogenous activator of PKC, were observed in sympathetic neurons treated with CNTF. However, neither CNTF nor LIF stimulated the hydrolysis of phosphatidylinositol 4,5‐bisphosphate. These observations suggest that a common PKC‐dependent pathway, which is independent of phosphatidylinositol 4,5‐bisphosphate hydrolysis, mediates the cholinergic stimulating effects of CNTF, LIF, and cell‐cell contact in cultured sympathetic neurons.