EFFECTS OF FETAL CALF SERUM AND DISRUPTION OF CADHERIN FUNCTION ON THE FORMATION OF BILE CANALICULI BETWEEN HEPATOCYTES

The polarization of hepatocytes to form a connected network of bile ca naliculi (BC) is necessary for the function of the liver. Hepatocyte p olarization may be controlled by soluble factors and/or physical inter actions between cells. Monolayer cultures of embryonic chicken hepatoc ytes in DMEM supplemented with ornithine, dexamethasone, and insulin e xpress BC-specific antigens for at least 7 days. However, BC-specific antigen expression is lost within 3 days of culture initiation in DMEM containing 10% fetal calf serum. The dedifferentiating effects of fet al calf serum (FCS) can be reversed. Furthermore, cultures in medium c ontaining ornithine, dexamethasone, insulin, and 10% FCS appear identi cal to cultures grown in 10% FCS alone. Thus FCS contains a soluble in hibitor of hepatocyte polarization. Aggregate cultures grown in suspen sion maintain hepatocyte polarization for 10-12 days. This may be due to the increased cell-cell contact between hepatocytes in aggregate cu lture or to more normal contact with the extracellular matrix. We have evaluated the role of cadherin-mediated interactions on hepatocyte po larization. Anti-E-cadherin Fab' fragments disrupted the formation of long networks of BC in monolayer cultures but did not stop polarized e xpression of BC-specific antigens. The BC antigens in anti-E-cadherin- treated cells were concentrated in small areas between cells and were present at lower levels uniformly on the cell surface. These results i ndicate that E-cadherin is required for the formation of extended BC n etworks, but that other factors are responsible for maintaining the sy nthesis and localization of BC-specific antigens. (C) 1994 Academic Pr ess, Inc.