A virus-induced non-virion antigen specific for transformation at the surface of RSV-transformed fibroblasts

NEW antigenic specificities expressed at the surface of virus-transformed cells are considered to be due to the insertion of virus structural proteins into the plasma membrane (for review see ref. 1). However, there is evidence far the non-identity of some tumour antigens at the surface of virus-transformed cells with virion proteins^2-5. For example, in the avian system, Rous sarcoma virus (RSV)-induced chicken sarcomas express at their surface a tumour-specific surface antigen (TSSA). The idea that the TSSA is not a virus structural protein, although under control of a viral gene, has been debated^3,6-8. We report here our studies on the antigenic composition of hamster fibroblasts transformed in vitro by RSV mutants, either defective for the synthesis of envelope glycoproteins (env^-) or temperature-sensitive for the ability to transform the host cell (ts). We found that these cells expressed at their surface a tumour-specific antigen with the following properties: (1) it is expressed at the surface of hamster cells transformed by RSV but not by unrelated RNA or DNA oncogenic viruses; (2) it is expressed by RSV-transformed cells of different animal species; (3) it is not one of the known structural virion proteins; (4) in the temperature-sensitive mutant-transformed cells its expression correlates with the expression of the transforming gene.