Tyrosine phosphorylation in cells treated with transforming growth factor‐β

Abstract

Cells stimulated with epidermal growth factor (EGF) or any one of a diverse group of other mitogenic agents display an increased tyrosine phosphorylation of a pair of 42,000 M_r proteins. Transforming Growth Factor-β (TGF-β) is able to potentiate the mitogenic effects of Epidermal Growth Factor on some fibroblastic cells (such as the NRK-49F cell line) and, in addition, permits the anchorage-independent growth of these cells. In this study we asked whether these growth-regulatory actions of Transforming Growth Factor-β are associated with changes in tyrosine phosphorylation of cellular proteins, in particular the 42,000 M_r proteins. We found no effect of Transforming Growth Factor-β on the extent or time-course of tyrosine phosphorylation, either by itself or in combination with Epidermal Growth Factor. Since the tyrosine phosphorylation of the 42,000 M_r proteins is stimulated both by receptors with tyrosine kinase activity and by diacylglycerol analogs (but not by Transforming Growth Factor-β), we suggest that the activity of the receptor for Transforming Growth Factor-β is linked neither to tyrosine phosphorylation nor to phosphatidyl inositol turnover.