OPPOSING REGULATION OF CILIARY NEUROTROPHIC FACTOR RECEPTORS ON NEUROBLASTOMA-CELLS BY DISTINCT DIFFERENTIATING AGENTS

We have used SH-SY5Y neuroblastoma cells as a model for differentiatin g neurons to examine the mechanisms that regulate responses to the neu ropoietic cytokine ciliary neurotrophic factor (CNTF), Retinoic acid a nd 12-O-tetradecanoyl-phorbol-13-acetate (TPA) each induced differenti ation of SH-SY5Y cells, Cells treated for 24 h with retinoic acid (10 mu M) showed a threefold increase in I-125-CNTF binding sites and were up to five times more sensitive to CNTF than untreated cells in stimu lating the tyrosine phosphorylation of the transcription factor STAT3, TPA (10 nM) induced a transient 42% decrease in I-125-CNTF binding si tes after 4 h of treatment that recovered to near control levels after 7 h of continuous exposure. TPA-treated cells showed a decreased sens itivity to CNTF and a sevenfold decrease in levels of STAT3. The retin oic acid-induced increase in I-125-CNTF binding could be prevented by administration of either cycloheximide or actinomycin D, whereas neith er agent altered the TPA-induced decrease in I-125-CNTF binding. In ad dition, levels of mRNA for both the CNTF receptor alpha and gp130 subu nits increased twofold as measured by RNase protection after treatment with retinoic acid for 30 h, The increase in CNTF receptor alpha subu nit mRNA was not due to a decrease in its turnover rate, and therefore , was likely due to an increase in gene expression, Thus, retinoic aci d and TPA regulate CNTF receptors on neuroblastoma cells differently, and the results demonstrate the importance of transcriptional control of CNTF receptors and also implicate translational and post-translatio nal mechanisms in the regulation of cytokine receptors and responses o n neurons. (C) 1997 John Wiley & Sons, Inc.