Expression of a human polyomavirus oncoprotein and tumour suppressor proteins in medulloblastomas

L Del Valle¹, J Baehring³, C Lorenzana⁴, A Giordano⁴, K Khalili¹ and S Croul²

¹ The Center for NeuroVirology and Cancer Biology, Temple University, Philadelphia, PA 19122, USA
² Department of Pathology and Laboratory of Medicine, MCP/HU School of Medicine, 3300 Henry Ave, Philadelphia, PA 19129, USA
³ Department of Neurology MCP/HU School of Medicine, Philadelphia, PA 19102–1192, USA
⁴ Department of Pathology, Anatomy, and Cell Biology, Jefferson Medical College, Philadelphia, PA 19107, USA

Correspondence to:
Dr Croul Sidney.Croul{at}Drexel.edu

Aims—Although the aetiology of medulloblastoma remains elusive, several lines of evidence suggest an association with the human neurotropic polyomavirus JC and 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 and inactivate tumour suppressor/cell cycle regulatory proteins, such as p53 and the retinoblastoma family of proteins.

Methods—To examine potential relations between these factors, immunohistochemistry was used to determine associations between the T antigen and the expression of p53 and the retinoblastoma proteins pRb, p107, and 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.

Key Words: medulloblastoma • T antigen • p53 • retinoblastoma protein

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