Presence of transforming growth factors in human breast cancer cells.

Conditioned medium (CM) from a human mammary carcinoma cell line, MCF-7, and ten individual clones derived from these cells was examined for the presence of transforming growth factors (TGFs). Concentrated CM from all of the MCF-7 cell lines was found to stimulate the anchorage-independent growth of normal rat kidney cells in soft agar and to inhibit the binding of epidermal growth factor (EGF) to mouse NIH/3T3 fibroblasts and to A431 human epidermoid carcinoma cell membranes. The soft agar stimulating activity was heat stable but sensitive to treatment with dithiothreitol.

Effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the growth inhibitory and increased phosphatidylinositol (PI) responses induced by epidermal growth factor (EGF) in A431 cells.

Epidermal growth factor (EGF) inhibited the growth of A431 human epidermoid carcinoma cells. The tumor promoting, phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) also retarded A431 cell growth. Addition of both TPA and EGF inhibited cell growth in an additive or synergistic manner depending upon the initial plating density of the cultures.

Arrest of synthesis of specific proteins at the onset of mammary tumor regression.

MTW9 mammary carcinoma regressing after removal of mammotropin stimulation was used as a model to test the hypothesis that the augmented activity of lysosomal enzymes observed during regression may be triggered by a modification of the protein composition of the cytoplasm. In support of the hypothesis, we observed that: (a) the pattern of leucine incorporation into cytosol proteins differs between growing and regressing tumors; (b) the difference is localized in three bands of the electrophoretic pattern; and (c) the change in pattern appears within 6 hr after hormone removal, about 4 hr after prolactin levels in blood were below the concentration needed by MTW9 to grow. These observations are in line with our previous finding of an increased susceptibility of cytosol proteins to proteolytic digesion during MTW9 regression.