Specific dephosphorylation of membrane proteins in Rous sarcoma virus-transformed chick embryo fibroblasts

Abstract

Chick embryo fibroblasts (CEF) infected with avian sarcoma virus become rapidly tranformed as a result of expression of the viral src gene in the form of a single polypeptide of MW 60,000 (pp60src) with protein kinase activity and suggested preferential association with the plasma membrane. Studies with normal avian and mammalian cells revealed the presence of an antigenically related protein which seems to have similar kinase activity, but which is present at less than 1% of the levels of virally induced src protein found in transformed cells. As dynamic protein phosphorylation is important in numerous regulatory processes, the phenotypic expression of tranformation may arise from an imbalance in one or more regulatory mechanisms that are controlled by protein phosphorylation. The cell membrane is affected during transformation, including its phosphotransferase activity. The latter was shown using isolated membrane fractions whose properties may be changed during preparation. Therefore, the phosphorylation state of individual membrane proteins found in intact normal and RSV[Rous sarcoma virus]-transformed cells were compared and the identification of 2 heavily phosphorylated, acidic membrane proteins in normal CEF which are specifically dephosphorylated on transformation by wild-type and temperature-sensitive Rous sarcoma viruses is reported.