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Having determined the complete amino acid sequence of a cytosolic phosphatase purified from bovine liver, we studied the role of this enzyme (referred to as 'PTPase') in the control of cell proliferation. We used NIH/3T3 fibroblasts, both normal and transformed by the oncogenes v-erbB, v-src, and v-raf: a synthetic gene coding for PTPase was transfected into, and overexpressed in, normal and transformed NIH/3T3 cells with resulting inhibition of cell growth. Inhibition of proliferation correlated with the level of foreign PTPase; growth in soft agar was also inhibited in transformants overexpressing the enzyme. However, PTPase overexpression did not inhibit the rapid turnover of inositol lipids stimulated by platelet-derived growth factor. We conclude that this novel PTPase is active on cell type-specific signalling substrates that control normal and transformed fibroblast proliferation.

In several cell types heparin exerts an antiproliferative action; here we report that heparin inhibited the growth of human epidermoid carcinoma A431 cells. Heparin binding to the cell surface was necessary for growth inhibition; binding was influenced by the molecular weight of heparin. Inhibition of A431 cell proliferation was evident in the presence and in the absence of serum, thus indicating that heparin did not act by binding and 'subtracting' nutrients or other serum factors. In confluent A431 cells, EGF induced DNA synthesis, but heparin did not inhibit this effect; consistently, it did not affect inositol lipid turnover triggered by EGF or bradykinin.

We examined the level of 1,2-diacylglycerol and inositol phosphates in normal and EJ-H-ras-transformed BALB/3T3 fibroblasts by prelabelling the cells with [3H]glycerol, [3H]inositol, [14C]glucose, [14C]arachidonic acid, and [14C]palmitic acid. Steady-state level of inositol phosphates, however, was the same in control and transformed cells. Diacyglycerol labelling by [14C]arachidonic acid was the same in control and transformed cells. Insulin dramatically increased diacylglycerol labeling by [14C]glucose in normal cells, whereas it did not affect ras-transformed fibroblasts. Neurotransmitter-induced inositol lipid turnover was greatly enhanced in ras-transformed cells; conversely, platelet-derived growth factor and thrombin-stimulated normal cells to a greater extent than transformed fibroblasts. Taken together these results suggest that ras transformation may induce multifarious effects on signal transduction: it may cause de novo synthesis of diacylglycerol and subversion of neurotransmitter and growth factor receptor coupling to inositol lipid metabolism.