[Characterization of a transforming growth factor produced in rat cells transformed by an avian sarcoma virus].

Transformation of rat cells by avian sarcoma viruses (ASVs) induced the release of transforming growth factors (TGFs), which transiently promote anchorage-dependent untransformed BALB3T3 clone A31 cells to form progressively growing colonies in soft agar, into serum-free conditioned medium. A new class of TGF, which is a heat and acid-labile protein with a molecular mass of 12,000 daltons, was isolated and purified from an ASV-transformed rat cell line, 77N1, derived from NRK cells. The TGF from 77N1 did not bind to epidermal growth factor membrane receptors. We observed specific in vitro phosphorylation of several membrane proteins from A31 cells in the presence of the TGF.