Ethanol inhibits growth factor induction of DNA synthesis in vivo and in vitro. The long-term objective of our work is to identify the mechanisms involved. We will continue to test the HYPOTHESIS that ethanol """"""""desensitizes"""""""" hepatocytes to the growth promoting effects of trophic factors by influencing the propagation of cAMP-dependent signals. In support of this theory, we have shown that chronic ethanol treatment distorts normal regenerative changes in G protein expression, causing a relative over-expression of inhibitory G proteins which blocks prereplicative induction of adenylyl cyclase activity and cAMP synthesis. The latter is correlated with impaired regenerative induction of at least one cAMP-regulated liver gene. Present efforts focus on identifying additional steps involved in the propagation of membrane-initiated, cAMP signals in order to define a molecular basis for cAMP growth regulation. Recent evidence indicates that cAMP can either stimulate or inhibit trophic signals, and suggests that the timing of cAMP induction may determine whether cAMP promotes or aborts proliferation. This insight may clarify how both acute and chronic ethanol consumption, which exert opposite effects on cAMP synthesis, each inhibit hepatocyte proliferation. That is, by increasing cAMP acutely, ethanol may abort the immediate induction of mitogen-activated kinases. However, adaptation to chronic ethanol consumption, which inhibits later accumulation of cAMP, may prevent induction of certain genes required for cell cycle progression. To test this theory we will address the following SPECIFIC AIMS: 1) Determine the effects of acute ethanol consumption on cAMP synthesis and the induction of mitogen-activated kinases after partial hepatectomy (PH); 2) Determine if chronic ethanol consumption inhibits post-PH induction of 2 growth-regulatory genes (C/EBP B and cyclin A) that are transcriptionally activated by cAMP, and discover if ethanol effects mimic those of other agents that decrease hepatic cAMP activity after PH; 3) Delineate the molecular basis for the acute and chronic effects of ethanol on mitogen-activated kinases, cAMP-dependent growth regulatory genes and hepatocyte proliferation by manipulating ethanol exposure, cAMP levels, and the activity of cAMP dependent protein kinase A (PKA) in primary hepatocyte cultures; and 4) Stably transfect expression vectors for Gsalpha, C/EBP B and cyclin A into a conditionally-transformed adult hepatocyte line to more directly evaluate the impact of ethanol-associated alterations in cAMP-dependent signalling on hepatocyte proliferation. Such information will identify specific cellular targets that may be particularly vulnerable to ethanol and suggest novel strategies to improve liver regeneration in alcoholics.
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