Detection of a complex of SV40 large tumor antigen and 53K cellular protein on the surface of SV40-transformed mouse cells

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Abstract
The possible interaction between simian virus 40 (SV40) large tumor antigen (T-ag) and cellular proteins in the plasma membrane of SV40-transformed mouse cells was investigated. The presence of SV40 T-ag, 53,000 (53K) cellular protein, and histocompatibility (H-2) antigens on the surface of SV40-transformed cells was demonstrated by immunofluorescence. The use of lactoperoxidase-catalyzed cell surface iodination and a differential immunoprecipitation technique established that large T-ag is associated with the 53K host-coded protein on the surface of the transformed cells. In contrast, no detergent-stable complex between large T-ag and H-2 antigens was detected. Both labeled T-ag and 53K protein were coprecipitated from surface-iodinated SV40-transformed cells by monoclonal antibodies directed against either the viral or the cellular protein. Based on the unique antigenic sites recognized by the anti-T monoclonal antibodies, it appears that both the carboxy and amino termini of the T-ag polypeptide are exposed on the surface of SV40-transformed mouse cells. The nature of the association between surface T-ag and 53K protein, as well as that between the molecular complex and the plasma membrane, remains to be determined. The possible effect of the surface-associated T-ag/53K complex on cellular proliferation is considered.