Characterization of the surface proteins of SV40-transformed mouse and human cells: absence of SV40-specific proteins.

The proteins of a number of SV40- and spontaneously transformed mouse and human cell lines were compared in an effort to identify a surface protein which would correspond to the SV40 tumor-specific transplantation antigen (TSTA). Analysis of the one- and two-dimensional electrophoretic patterns of 35S-methionine-labelled total proteins and 125I-labelled surface proteins of several of these cell lines failed to reveal the presence of proteins specific to transformation by SV40. Antisera were prepared against SV40- and spontaneously transformed mouse cells in syngeneic mice. In serological assays, these antisera reacted with surface antigens common to both SV40- and spontaneously transformed mouse cell lines. Electrophoretic analysis of the 125I-surface-labelled proteins which these antisera immunoprecipitated from extracts of SV40- and spontaneously transformed mouse and human cells identified a set of common surface proteins with apparent molecular weights of 15, 46, 50, 72, 77, 105, 150 and 230kdal. No SV40-specific surface proteins were detected. Two of the transformed cell surface proteins (105 and 150kdal) were present as well in membrane fractions of 35S-methionine-labelled primary mouse kidney cultures. The proteins of the primary cultures could not be iodinated by lactoperoxidase suggesting that these proteins were present at a "cryptic" location at the surface of normal cells. We were not able to obtain serological or immunochemical evidence for the presence of SV40 large T-antigen at the surface of any of the SV40-transformed cell lines tested using either hamster anti-SV40 tumor sera, a rabbit antiserum against SDS-denatured gel-purified large T-antigen or antisera against SV40-transformed mouse cells. In conjunction with the report that large T-antigen released from disrupted SV40-transformed cells will bind to cell surfaces (Lange-Mutschler and Henning, 1982), we consider the possibility that the specific rejection of SV40-induced tumors by sensitized animals is the result of immunological reactions against both common transformation-related surface antigens and SV40 T-antigen from disrupted cells that has bound to the surface of other tumor cells.