Reciprocal modulation of growth and liver functions of mature rat hepatocytes in primary culture by an extract of hepatic plasma membranes.

A cell-surface modulator with the ability to mimic the reciprocal effects of cell density on cell growth and liver-specific functions of mature rat hepatocytes in primary culture (Nakamura, T., Yoshimoto, K., Nakayama, Y., Tomita, Y., and Ichihara, A. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 7229-7233) was solubilized with 4% octyl glucoside and 4 M guanidine HCl from plasma membranes purified from adult rat liver. The membrane-free modulator showed activities for inhibition of DNA synthesis stimulated by insulin with epidermal growth factor and stimulation of tyrosine aminotransferase induction by dexamethasone. The apparent Mr of the factor was estimated as 670,000 by gel filtration on a Sephacryl S-400 column equilibrated with 0.5% octyl glucoside and 4 M guanidine HCl. The modulator was heat-labile and sensitive to trypsin. These results suggest that the reciprocal regulations of cell growth and hepatocyte-specific functions are mediated via cell to cell contact by a cell-surface modulator(s) that is an integral membrane protein.