DIFFERENTIAL INHIBITION OF EPIDERMAL GROWTH-FACTOR SIGNALING PATHWAYSIN RAT HEPATOCYTES BY LONG-TERM ETHANOL TREATMENT

Background & Aims: Long-term ethanol intake suppresses liver regenerat ion in vivo and ethanol interferes with epidermal growth factor (EGF)- induced DNA synthesis in vitro. Therefore, the effects of long-term et hanol treatment on EGF-activated signaling reactions in rat hepatocyte s were investigated, Methods: Hepatocytes from long-term ethanol-fed r ats and pair-fed controls were stimulated with EGF (0.5-20 nmol/L) for 15-120 seconds. Tyrosine phosphorylation of EGF: receptor (EGFR), Shc , and phospholipase-C gamma 1 (PLC gamma), and growth factor receptor binding protein 2 (Grb2) coprecipitation with EGFR and She were analyz ed by Western blotting. Results: EGFR autophosphorylation was suppress ed at all EGF concentrations in ethanol-fed cells compared with pair-f ed cells, without significant differences in total EGFR protein or EGF R tyrosine kinase activity detected in cell lysates, suggesting that i ntracellular factors suppressed EGFR function. EGF-induced PLC gamma t yrosine phosphorylation and inositol 1,4,5-trisphosphate (InsP(3)) for mation were suppressed, but cytosolic [Ca2+], elevation was little aff ected, indicating enhanced InsP(3)-mediated intracellular Ca2+ release in ethanol-fed cells, Grb2 binding to EGFR was suppressed, but EGF-in duced She tyrosine phosphorylation and Grb2 association with She were not significantly decreased. Conclusions: Long-term ethanol feeding su ppressed EGF-induced receptor autophosphorylation in rat hepatocytes w ith differential inhibition of downstream signaling processes mediated by PLC gamma, Shc, and Grb2, Altered patterns of downstream signals e manating from EGFR may contribute to deficient liver regeneration in c hronic alcoholism.