Serum dependence of expression of the transformed phenotype: Experiments with subline of mouse L fibroblasts adapted to growth in serum-free medium

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Abstract
Characteristics of LSF cells grown in serum‐containing and serum‐free medium were compared. LSF is a subline of the L‐strain of mouse transformed fibroblasts adapted to continuous growth in serum‐free medium. Proliferation of LSF cells in monolayer on solid substratum was almost similar in serum‐containing and in serum‐free media. However, several other characters were found to be altered by the addition of serum to the serum‐free medium: ability of cells to form colonies in semi‐solid medium increased considerably; agglutinability of cells by Concanavalin A increased; uptake of 2‐deoxy‐D‐glucose by the cells increased considerably; ability of cells to metabolize benzo (a)pyrene was inhibited; cell morphology was altered and, in particular, the cells became less spread on the substratum and density of microvilli on the cell surface increased. All these changes induced by serum were reversed by transfer of the cells back into serum‐free medium. Thus, addition of serum increased the expression of a number of cellular traits characteristic of transformed phenotype, while in serum‐free medium partial phenotypic reversion of transformation was observed. A possible role of serum in the expression of the transformed phenotype is discussed. It is pointed out that cell lines adapted to growth in serum‐free medium provide an experimental system convenient for analysis of the effects of different serum components on the cell phenotype.