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Feb. 19, 2002 |
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Viral proteins may be linked to human brain tumors PHILADELPHIA -- Feb. 19, 2002 (Cancer Digest) -- A common virus may be the cause of one form of brain cancer and may play a role in the development of the most frequent type of malignant brain tumor in children say researchers. The researchers found the evidence of the viral genes in a type of brain cancer called medulloblastoma tumors. Led by Dr. Luis Del Valle, and Dr. Kamel Khalili, of Temple University's Center for Neurovirology and Cancer Biology, the research team published their findings in the Feb. 20 issue of the Journal of the National Cancer Institute. "There is a virus, the JC Virus (JCV), which infects greater than 70 percent of the human population worldwide during early childhood," Khalili said in a press release. "What we have shown in this study is that medulloblastoma tumors that we see in pediatrics, have in some portions, the genome of the JC Virus," says Khalili. "This genome expresses the viral proteins T antigen, which has oncogenic potential, and an agnoprotein, whose function is unknown." In the current study, the authors found the gene that produces agnoprotein in 69 percent of 16 medulloblastoma samples, and the gene that produces T antigen in 65 percent of 20 medulloblastoma samples. The researchers also found agnoprotein and T antigen in about 50 percent of the samples, with some samples containing only agnoprotein. They conclude that, "the finding of agnoprotein expression in the absence of T-antigen expression suggests a potential role for agnoprotein in pathways that control the development of JCV-associated medulloblastomas." According to Khalili, the JC Virus most likely infects humans through the upper respiratory tract and remains in a latent stage in most people throughout their lives, and, in some cases, causes very minor problems that don't require clinical treatment. However, in people whose immune systems go down, either through kidney transplantation or an illness such as AIDS, the JCV can become active and lead to a fatal disease of the central nervous system and brain called progressive multifocal leukoencephalopathy (PML). How the two proteins the researchers found cause brain tumor is not clear. They theorize that T antigen may cause brain tumors in part by blocking tumor suppressor proteins such as p53 and pRb. The role of agnoprotein in the development of brain tumors is unknown. Recent studies suggest, however, that the interaction of T antigen with agnoprotein may affect T antigen's ability to control cell growth. In either case, the researchers emphasize that all they have found is a link, not a cause. Khalili says that the questions now facing researchers are whether or not the JC virus actually causes tumors; whether the tumors formed because of other elements and the virus helped as a co-factor; or whether something else causes the tumors and the presence of the virus is a mere chance association. "We know that the agnoprotein has the capacity to associate with the T antigen," says Khalili, who has been studying the molecular biology of the JC Virus for nearly two decades. "So it seems that the communication between these two viral proteins may impact the ability of the virus to induce brain tumors. What we are trying to show in this study is that the JC virus has the ability to do more than just cause PML. We have a virus in our bodies that may have the potential to cause tumors." |
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