Plasma membrane proteins exposed on the outer surface of control and Rous sarcoma virus-transformed hamster fibroblasts

Nature of the antigenic complex recognized by T lymphocytes. IX. Direct immunochemical demonstration of nominal antigen on the macrophage cell surface

As an initial approach to macrophage (M phi) antigen handling, guinea pig M phi pulsed with the radiolabeled terpolymer L-glutamic acid, L-lysine, L-tyrosine (GLT) were modified with the cell surface-specific probe 2,4,6-trinitrobenzenesulfonic acid either immediately after pulsing (fresh) or 24 h after pulsing (aged); nonidet P-40 extracts were prepared from these cells and analysis of these extracts with anti-trinitrophenyl antisera was performed in a quantitative radioimmunoassay. Such experiments indicated that fresh GLT-pulsed M phi contained a pool of intracellular GLT as well as a distinct pool of cell surface GLT. In contrast, aged GLT-pulsed M phi lacked intracellular GLT but expressed GLT on the cell surface. In addition, a pool of cell surface GLT was also detected on Ia-M phi and on M phi from guinea pigs which were nonresponders to GLT. Thus, this study provides a direct demonstration of the presence of exogenous antigen on the M phi cell surface. However, the cell surface expression of GLT does not appear to be an exclusive property expressed by functional Ia+ antigen-presenting M phi.

Identification and partial characterization of five major membrane glycoproteins of BHK fibroblasts

Five major membrane glycoproteins of the BHK-B4 hamster fibroblast plasma membrane have been identified by binding specific rabbit antibodies to the cell surface and by recovering the detergent solubilized immunocomplexes with Protein A-Sepharose immunoadsorption. These glycoproteins, designated as gp45, gp65, gp95, gp130 and gp140, are exposed at the cell surface since: (i) they were accessible to antibodies in intact viable cells; (ii) they were radioiodinated by the lactoperoxidase-glucose oxidase procedure; and (iii) they were cleaved by proteolytic enzymes in conditions affecting only the cell surface. Among these glycoproteins the gp130 is the predominant component and its exposed portion is characterized by lack of sensitivity to trypsin cleavage. Glycoproteins of different molecular weight, but immunologically related to the major hamster membrane glycoproteins, have been detected at the surface of both rat and mouse fibroblasts.

Interaction between cellular and viral genes in the expression of the RSV-induced transformation-specific cell-surface antigen VCSA

Transformation of BHK hamster fibroblasts by an env- strain of Rous sarcoma virus (RSV) leads to the appearance at the cell surface of a virus-induced nonvirion antigen (VCSA), specific for transformation, whose expression is controlled by the transforming src gene. Previous work has shown that a rabbit anti-VCSA serum lyses specifically, in the presence of complement, 51Cr-labelled RSV-transformed cells from different animal species. Now, by competition experiments with a panel of different unlabelled cells we show that the VCSA expressed on RSV-transformed hamster fibroblasts is a complex of at least three distinct antigenic specificities: (1) one expressed on all RSV-transformed fibroblasts, regardless their species and the subgroup or strain of the transforming virus; (2) one cross-reacting with a cell-surface antigen (CSA) expressed at various degrees on untransformed avian fibroblasts, but not on mammalian fibroblasts; (3) one species-specific, present only on RSV-transformed hamster fibroblasts. It is concluded that VCSA is a complex of several antigenic determinants, and that some of these differ in different cells transformed by RSV. This observation indicates that VCSA expression at the cell surface is likely to be the result of the interaction between the viral src gene product pp60src with host cell gene(s) or gene product(s), rather than the simple expression of this molecule at the cell surface.

Tumor-specific and tumor-associated membrane antigens of Rous sarcoma virus transformed hamster fibroblasts

Hamster fibroblasts transformed by an env- strain of Rous sarcoma virus (RSV) express at their surface tumor-associated antigens of unknown origin and a tumor-specific antigen (VCSA) which is not expressed by hamster fibroblasts transformed by unrelated DNA or RNA oncogenic viruses. This antigen was detectable by rabbit antibodies and a complement-dependent 51Cr-release cytotoxicity assay and is common to RSV-transformed cells of different animal species. By comparing the anti-VCSA serum which antisera directed against purified gp85, gs-proteins, reverse transcriptase or detergentlysed virus particles, it was shown that VCSA is not a known virion structural protein. Moreover, VCSA expression does not correlate with viral replication since it is not detectable in chick embryo fibroblasts productively infected with the transformation-defective virus RAV-1 which shares virus structural genes with RSV. Finally, in hamster cells transformed by an RSV mutant, temperature-sensitive for the ability to transform the host cell, VCSA expression at the cell surface correlates with the expression of the transforming gene.