Inhibition of cellular response to platelet‐derived growth factor by low Mr phosphotyrosine protein phosphatase overexpression

The role of low M(r) phosphotyrosine protein phosphatase (PTPase) in the control of cell proliferation was studied. A synthetic gene coding for PTPase was transfected and expressed in NIH/3T3 fibroblasts. The effects of the enzyme were particularly evident when cells were stimulated by platelet-derived growth factor (PDGF). The mitogenic response to PDGF was decreased and the inhibition reached 90%. This effect was more pronounced with respect to fetal calf serum stimulation. Hormone-dependent autophosphorylation of the PDGF receptor was significantly reduced. These results demonstrate that low M(r) PTPase, a cytosolic enzyme, not only affects cellular response to PDGF but also reduces the membrane receptor autophosphorylation.