Characterization of the surface proteins of SV40‐transformed mouse and human cells: Absence of SV40‐specific proteins

Abstract

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.

In vivo induction of tumor‐specific immunity by glycolipid extracts of SV40‐transformed cells

“…This is difficult to demonstrate directly since in order to elicit host immune responses, TSTAs must be present at the cell surface. Attempts to localize SV40-specific proteins in the plasma membranes of SV40-transformed cells have led to contradictory conclusions (Tevethia et al, 1979;Rose and Weil, 1983). According to Soule et al (1980), the large T antigen, present in the nuclei of SV40-transformed cells, may also be detected in the plasma membranes, where it possesses distinct antigenicity; a post-translational change of the protein at the plasma membrane level would possibly be related to TSTA activity.…”