[Regulation of the expression of the c-fos gene in cells, reverting from being transformed to the pseudonormal phenotype].

Regulation of c-fos expression in mice sarcoma cell lines CBA and C3H was investigated. Each of the cell lines was represented by a pair of clones: the tumorigenic and the one, which was produced from it by cloning. It was found, that c-fos expression in cells of the pseudonormal phenotype was similar to that in the normal fibroblasts. Experiments with cells reverted to pseudonormal phenotype transfected transiently or permanently with an indicator plasmid fos-cat have shown, that a 600 bp sequence of the c-fos promotor including the TATA site, provides the expression level of the chloramphenicol acetyltransferase, correlating with the level of the c-fos mRNA expression. In the tumorigenic cells, permanent high activity of the cat gene expression was observed which was comparable to that in the normal fibroblasts stimulated by the embrionic serum or TPA. Activity of the transcription factors interacting with regulatory elements SRE, DSE, TRE did not correlate with the c-fos expression level in all the cells.