Showing papers by "Joan S. Brugge published in 1983"

Isolation of monoclonal antibodies that recognize the transforming proteins of avian sarcoma viruses.

Abstract: Thirteen clones of hybrid cells which synthesize antibodies directed against the Rous sarcoma virus (RSV) transforming protein, pp60src, were isolated. Mouse myeloma cells were fused with spleen cells from mice that had been immunized with purified pp60src from bacterial recombinants which direct the synthesis of the RSV src gene. The hybridomas which survived the selection medium were screened by immunoprecipitation of pp60src from 32P-labeled lysates of RSV-transformed cells. Monoclonal antibodies produced by subclones derived from 13 hybridomas recognized pp60src encoded by the Schmidt-Ruppin and Prague strains of RSV and the cellular homolog of pp60src. Antibody from clone 261 had a high affinity for the viral yes gene product, and antibodies from clones 443 and 463 recognized the transforming proteins encoded by viruses containing the related transforming genes fps and ros. Several other clones had a low affinity for the viral yes, fps, and ros gene products which could be detected by in vitro phosphorylation of the transforming proteins after immunoprecipitation with the monoclonal antibody. All of the monoclonal antibodies allowed phosphorylation of pp60src and casein in an immune complex-bound reaction.

Neural tissues express high levels of the cellular src gene product pp60c-src.

Abstract: Chicken embryo tissues were examined for the expression of pp60c-src, the normal cellular homolog of the transforming protein of Rous sarcoma virus. Three assays, including a solid-phase radioimmunoassay, a competitive radioimmunoprecipitation assay, and an immune complex protein kinase assay, were employed. Elevated levels of pp60c-src were detected in lysates from several neural tissues, including brain, retina, and spinal ganglia. Other tissues contained 8- to 10-fold-lower levels of pp60c-src, levels comparable to those found in chicken embryo fibroblasts. Expression of pp60c-src in brain tissues was also shown to vary with the developmental stage of the embryo.

Interaction between the Rous sarcoma virus transforming protein and two cellular phosphoproteins: analysis of the turnover and distribution of this complex.

Abstract: The transforming protein of Rous sarcoma virus (RSV), pp60src, was previously shown to associate with two cellular proteins of Mr 90,000 and 50,000 in RSV-transformed chicken cells. In this report, we demonstrate that this interaction is specific for a discrete population of pp60src molecules. Newly synthesized pp60src was found to preferentially associate with pp90 and pp50 to form a short-lived complex. The half-life of this complex varied from 9 to 15 min in cells transformed by nondefective strains of RSV. This interaction between pp60src, pp50, and pp90 took place in a soluble fraction of the cell, and the complex-bound pp60src molecules were not phosphorylated on tyrosine. These results suggest that pp90 and pp50 may be involved in the processing of pp60src molecules before the association of pp60src with the plasma membrane. The kinetics of dissociation of this complex were shown to be altered in cells infected with viruses containing a temperature-sensitive defect in the src gene. When cells infected with these viruses were grown at the nonpermissive temperature, more than 90% of the pp60src molecules were associated with pp90 and pp50, and little or no dissociation was observed in a 3-h chase period. These results suggest that mutations in the src gene which affect the transforming activity of pp60src also affect the stability of the interaction of pp60src with pp90 and pp50.

Chapter 22. Tyrosine-Specific Protein Kinases

Abstract: Publisher Summary The enzymes that comprise tyrosine kinases can be distinguished from other protein kinases by a number of criteria, most notably, their specificity for phosphorylation of tyrosine residues The importance of these phosphotransferases is not merely a consequence of their tyrosine-specificity, but the evidence that all of the enzymes in this class appear to be associated with the regulation of cellular morphology and growth control At first, tyrosine phosphorylation is identified in association with the transforming proteins of several oncogenic viruses “Transforming” proteins are those polypeptides that are responsible for the initiation and maintenance of the transformed phenotype A second group of tyrosine-specific protein kinases has been identified in normal cells This group contains the membrane receptors for many cellular growth factors, including epidermal growth factor (EGF), insulin, and platelet derived growth factor (PDGF) Interaction of each of these factors with their respective cellular receptor results in activation of tyrosine-specific kinase activity associated with the receptor molecule The precise mechanism, whereby these tyrosine kinases interact with other cellular proteins to exert their biological effects, is presently unknown This review discusses the current state of knowledge on these two groups of tyrosine kinases