EPITHELIAL-MESENCHYMAL TRANSITION OF CULTURED RAT NEONATAL HEPATOCYTES IS DIFFERENTIALLY REGULATED IN RESPONSE TO EPIDERMAL GROWTH-FACTOR AND DIMETHYL-SULFOXIDE

Neonatal rat hepatocytes cultured in the absence of added growth facto rs dedifferentiate by epithelial-mesenchymal transition (EMT). This in volves the loss of their typical differentiation markers, the acquisit ion of a migrating morphology, and a change in the expression of the i ntermediate filament (IF) proteins. We attempted to determine whether the EMT of cultured neonatal rat hepatocytes could be modulated by fac tors that maintain and promote the differentiation state of adult and fetal hepatocytes such as epidermal growth factor (EGF) and dimethyl s ulfoxide (DMSO). By (H-3)-thymidine incorporation, Western blotting an alysis, now cytometry, and double-immunofluorescence studies, we found that both factors have marked but opposite effects on the EMT and on proliferation of neonatal liver cells. In DMSO treatment, albumin leve ls were higher than in the nontreated cells at all days studied. Moreo ver, DMSO reduced cytokeratin levels and inhibited cell proliferation, acquisition of the fibroblast-like morphology, and vimentin expressio n typical of the EMT. The increase in vimentin-positive cells in serum -free medium was not observed in DMSO cultures. EGF also increased alb umin levels at all days studied. In contrast, EGF treatment induced he patocyte proliferation and enhanced vimentin and cytokeratin expressio n. However, the increase in vimentin levels did not correlate with a s ignificant increase in the number of vimentin-positive cells. Moreover , vimentin-positive cells in EGF treatment were also cytokeratin-posit ive and albumin-positive, and they maintained epithelioid morphology i n spite of the vimentin network. These results indicate that EMT of cu ltured rat neonatal hepatocytes is differentially regulated in respons e to EGF and DMSO.