Negative growth control by a novel lowMrphosphotyrosine protein phosphatase in normal and transformed cells

Abstract
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.

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