Ethanol interferes with recovery from liver injury by desensitizing hepatocytes to trophic factors. Ethanol-induced interruptions in cAMP- dependent signal transduction may be involved in this process. Chronic ethanol treatment causes relative over-expression of an inhibitory G- protein and has correlated this with impaired activation of adenylyl cyclase, decreased hepatic cAMP, and inhibition of liver regeneration. Preliminary data suggest this latter effect may be more proximally mediated by changes in the nuclear expression of cAMP-responsive isoforms of CCAAT-Enhancer Binding Protein (C/EBP) transcription factors which normally inactivate C/EBP alpha, a major growth inhibitor. Regenerative changes in the expression of various C/EBP isoforms will be compared in ethanol-treated and pair-fed rates to verify ethanol-associated decreases in C/EBP beta expression and to evaluate the effects of ethanol treatment on the expression of other C/EBP isoforms. Next, cAMP concentrations will be manipulated in primary hepatocyte cultures to determine if (and how) changes in C/EBP expression are induced by cAMP. Since changes in C/EBP expression may modify C/EBP alpha function by altering dimerization, subsequent co-transfection and anti-sense experiments will be performed to vary concentrations of the affected (cAMP-induced) C/EBP isoforms and changes in C/EBP alpha DNA binding and trans-activation of C/EBP regulated promotes will be evaluated. Results from these studies will clarify important regulatory mechanisms for liver cell proliferation and differentiation and suggest novel strategies to prevent ethanol- induced aberrations in these processes.
