One of the more pronounced hepatic dysfunctions observed in animals chronically fed ethanol is a impairment in receptor-mediated endocytosis. Receptor-mediated endocytosis is responsible for the uptake and degradation of many biologically important molecules including hormones, growth factors and cytokines. Receptor-mediated endocytosis is also involved in the regulation of the expression of surface receptors and signal transduction. Thus, alterations in hepatic receptor-mediated endocytosis could be detrimental to the liver. Although, impairment in receptor-mediated endocytosis is well established in hepatocytes isolated from ethanol fed animals, the mechanism(s) of this impairment have yet to be elucidated. Furthermore, the direct involvement of ethanol metabolism in this defect has yet to be demonstrated. Many mechanisms for the hepatic cell injury associated with chronic ethanol abuse have been proposed. One attractive, though unproven mechanism, proposes that acetaldehyde forms acetaldehyde-protein adducts and through their accumulation eventually causes hepatic dysfunction. One of the main reasons that these underlying mechanisms of chronic ethanol oxidation have not been determined has been the lack of a stable in vitro hepatic model system for the study of chronic ethanol oxidation. The PI recently developed a cell line of hepatic origin that metabolized ethanol to acetaldehyde and produces acetaldehyde-protein adducts and proposes to use this cell line (HAD cells) to investigate impairments in epidermal growth factor signal transduction. The hypothesis is that alcohol dehydrogenase mediated oxidation of ethanol impairs the biological activities of the epidermal growth factor receptor. Inactivation of this receptor dramatically alters the ability of hepatocytes to respond appropriately to extracellular signals. Epidermal growth factor is an important hepatic mitogen. The binding of epidermal growth factor to its receptor activates an intrinsic tyrosine kinase, which initiates a signal transduction cascade resulting in cell proliferation.
The Specific Aims of this proposal are: 1) Determine what processes of epidermal growth factor receptor-mediated endocytosis are impaired by ethanol oxidation and exposure to acetaldehyde; 2) Investigate the effect of ethanol oxidation on the signal transduction pathway of the epidermal growth factor receptor in the recombinant HAD cells; 3) Investigate the possibility that acetaldehyde-protein adducts are responsible for the observed ethanol induced impairment of the epidermal growth factor receptor; and 4) Investigate the effects of ethanol oxidation on the mitogenic activities of epidermal growth factor in the recombinant HAD cells. By completing these studies, it is hoped that the investigators can determine the effects of chronic ethanol oxidation and exposure to acetaldehyde on the signal transduction of epidermal growth factor, thus leading to a greater understanding of the mechanisms of induced liver injury.
