Induction of plasma membrane alterations in AKR‐2B mouse embryo fibroblasts by endogenous growth factors from malignant human cells

AKR‐2B mouse fibroblasts were treated with 50 μg/ml of crude transforming growth factor (TGF) of human origin. Cell surface proteins of treated cells were radioiodinated and compared to untreated cells at various times after the addition of TGF. Treated cells showed a several‐fold increase (0˜6‐fold) in cell surface ¹²⁵I incorporation relative to normal cells at 24 h. Electrophoretic comparisons of treated and untreated cells showed large increases in the labelling of cell surface proteins of mol. wt. 50,000–90,000 from TGF‐exposed cells between 10 and 24 h post treatment. By 48 h post treatment, the electrophoretic profiles of TGF‐exposed cells had returned to a pattern similar to that of untreated cells. However, even after a 48 h exposure to TGF, the cells retained a transformed morphology indicating that the electrophoretic alterations were not simply due to the morphological transformation induced by TGF. The electrophoretic pattern of TGF‐treated cells at 24 h post treatment was similar to that of AKR‐2B cells permanently transformed by treatment with methylcholanthrene, but was clearly distinct from that induced by treatment of normal AKR‐2B cells with epidermal growth factor (EGF). EGF induced an increase in a protein of mol. wt. 60,000 in the electrophoretic profile taken 24 h post treatment. As with TGF, the appearance of electrophoretic profiles of EGF‐treated cells returned to ‚normal’ by 48 h. Again, these alterations did not appear to be dependent upon morphological changes since EGF‐treated cells showed a morphological transformation similar to that of cells treated with TGF, and this was maintained throughout the 48 h experimental period.