Absence of SV40 large T-antigen expression in human mesothelioma cell lines

Simian virus (SV) 40 and SV40-like DNA sequences have recently been detected in several types of human tumors, including malignant mesothelioma. However, the presence of SV40 DNA sequences is not sufficient to account for its possible role in tumor development because the viral proteins must be expressed and ultimately impair the function of relevant cell proteins, such as p53 and pRb. In this study we investigated SV40 large T antigen (SV40 Tag) protein expression in mesothelioma cell lines, established in our laboratory, by Western blotting, immunoprecipitation, and immunocytochemistry using Tag-specific mouse monoclonal antibodies (mAbs) Ab-1 (or Pab 419). By Western blotting of cell extracts, none of the mesothelioma cell lines expressed detectable amounts of SV40 Tag. However, we found that Ab-1 as well as Pab-101, another SV 40 Tag-specific mAb, may generate false-positive signals due to the fact that both antibody preparations are contaminated by a protein of similar size (90 kD) as SV40 Tag and react with the various secondary horseradish peroxidase-conjugated antimouse immunoglobulin Gs tested. The present study suggests that immunodetection of SV40 Tag protein may be puzzling because this contaminating Taglike protein may bind to particular cell structures, thereby generating false-positive signals.