Establishment of a fetal rat liver cell line that retains differentiated liver functions.

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Abstract
Fetal rat liver cells were transformed with a temperature-sensitive A mutant (tsA255) of SV40. A clonal cell line, RLA255-4, which was temperature-sensitive in the maintenance of the transformed phenotype, was isolated. This cell line expressed the transformed phenotype (rapid growth, high cell density, overgrowth of normal cells and cloning in soft agar) at the permissive temperature (33.degree. C) and the nontransformed phenotype (slower growth, lower saturation density, decreased efficiency of overgrowth of normal cells and lower cloning efficiency in soft agar) at the restrictive temperature (40.degree. C). The tsA255-transformed cells expressed differentiated liver functions under controllable conditions. At the permissive temperature, they produced low levels of albumin and transferrin, whereas at the restrictive temperature the transformed phenotype was lost and the production of these hepatic proteins was greatly enhanced. RLA255-4 cells contained functional receptors for glucagon, as shown by the stimulation of intracellular cyclic AMP accumulation by glucagon. The response to glucagon was dose-dependent (Kact [activation constant] = 5 .times. 10-8 M) and could be demonstrated in cells grown at both permissive and restrictive temperatures after 7 days in culture (i.e., at a cell density of approximately 4 .times. 105 cells/cm2 or higher). Addition of cortisol to the culture medium enhanced the glucagon response selectively at the restrictive temperature.