Expression of a human polyomavirus oncoprotein tumour suppressor proteins in medulloblastomas

Aims - Although the aetiology of medulloblastoma remains elusive several lines of evidence suggest an association with the human neurotropic polyomavirus JC its oncoprotein T antigen. The tumour forming properties of JC virus T antigen are the result at least in part of its ability to bind inactivate tumour suppressor/ cell cycle regulatory proteins such as p53 the retinoblastoma family of proteins. Methods - To examine potential relations between these factors immunohisto-chemistry was used to determine associations between the T antigen the expression of p53 the retinoblastoma proteins pRb p107 Rb2/p130 in eight medulloblastomas. Results - Only the three medulloblastomas with T antigen expression also showed nuclear positivity with antibodies to p53. Although immunohistochemistry detected nuclear labelling for pRb in five of the cases, the three that were positive for T antigen showed the highest pRb labelling. The retinoblastoma related proteins p107 and Rb2/p130 were also immunopositive in most T antigen positive medulloblastomas. Double label immunohistochemistry also demonstrated p53 and pRb positivity in the same cells that were T antigen positive. Conclusions - These correlations suggest that associations between T antigen and p53 and/or T antigen and pRb occur in some of these tumours. These data provide indirect evidence that JC virus, acting through T antigen, might be involved in the formation and progression of medulloblastoma.