Transforming Growth Factor-β1 Enhances Serum-Induced Dephosphorylation of the P53 Protein in Cell Lines Growth-Inhibited by this Factor

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Abstract
A 24 hr TGF-β1 treatment (4 ng/ml) of SV40-transformed WI38 embryonic fibroblasts (VA13 cells) causes a moderate but reproducible inhibition of their serum-stimulated growth. By immunoprecipitation with the PAb122 antibody, we show that serum stimulation of previously serum-deprived cells causes a dephosphorylation of the wild type P53 protein, which is accentuated by the TGF-%β1 treatment. The TGF-β1-enhanced dephosphorylation effect is also observed in two other cell lines growth-inhibited by TGF-β1, but which do not contain Large T (mink lung CCL64 and human KHOS cells). On the contrary, TGF-β1 treatment of the untransformed WI38 fibroblasts stimulates their growth, without affecting the phosphorylation of P53. Such treatment did not affect the expression of the corresponding mRNA nor the level of synthesis of the protein. The results suggest that the P53 protein could be a downstream target of TGF-β1 action on those cells growth-inhibited by the factor.