The full-length major capsid protein, VP1, of the human polyomavirus JC virus was cloned and expressed in Escherichia coli. VP1 protein expressed in E. coli self-assembled into capsid-like particles and caused haemagglutination of human O-type red blood cells. Caesium chloride density-gradient centrifugation analysis revealed that the capsid-like particles consisted of virionlike pseudovirion and empty capsid-like pseudocapsid populations. The morphology of pseudovirion and pseudocapsid particles was observed under the electron microscope. The pseudovirions contained DNA and RNA molecules but the pseudocapsids did not contain any nucleic acid, as analysed by DNA extraction. DNA-binding activity of VP1 was also demonstrated by the SouthWestern probing method in vitro. Furthermore, pseudocapsids were able to deliver exogenous DNA into human foetal kidney epithelial cells. These results indicate that recombinant JC virus VP1 is able to self-assemble into capsid-like particles and to package DNA in the absence of the minor capsid proteins, VP2 and VP3. This prokaryotic assembly system may facilitate the investigation of maturation mechanism(s) of polyomaviruses. Furthermore, capsid-like particles of JC virus VP1 generated in E. coli potentially could be used as a human gene transfer vector.

Although JC virus (JCV), a human polyomavirus, has been detected in colon cancers, the association between JCV and colon cancer remains controversial. In Taiwan, the prevalence of JCV infection in colon cancer patients has not been reported. Thus, the purpose of this study was to investigate JCV infection in colon cancers in Taiwan. Formalin-fixed, paraffin-embedded tissues from 22 colon cancer patients were examined in this study. Nested PCR was performed to detect viral genomic DNA. The product of the nested PCR flanking the JCV regulatory region was sequenced further. Viral large tumor protein, LT, and late capsid protein, VP1, were examined by immunohistochemistry (IHC). Nested PCR revealed JCV genomic DNA in 86.4% (19/22) of the colon cancer tissue samples. Both rearranged and archetypal genotypes of JCV were identified. Expression of JCV LT was positive in 63.6% (14/22) of the examined colon cancer tissue samples but not in any adjacent normal region. Expression of viral capsid protein VP1 was not detected in any of the tissues examined. The current study demonstrates that JCV genomic DNA was present in the examined colon cancer tissues. The genotypes of JCV in colon cancer tissues were also identified. Expression of viral early protein but not structural capsid protein was detected in the examined colon cancer tissues. Furthermore, a high prevalence of JCV infection in colon cancer tissues in Taiwan was also demonstrated.

The major capsid protein of human polyomavirus JC virus, VP1, has been cloned into a baculovirus genome and expressed in insect cells. The VP1 protein was expressed in the cytoplasm and transported into the nucleus. It was then purified by a sucrose cushion and CsCl density gradient centrifugation to near homogeneity. Electron microscopy showed that isolated recombinant VP1 protein selfassembled into a capsid-like structure similar to the natural empty capsid. Both chelator (EDTA) and reducing agent (DTT) are required to disrupt the capsid structure into the pentameric capsomeres, as demonstrated by haemagglutination assay and electron microscopy. These results suggest that JC virus VP1 can be transported into the nucleus and self-assembled to form capsid-like particles without the involvement of the viral minor capsid proteins, VP2 and VP3. In addition, metal ions and disulphide bonds appear to be important in maintaining the integrity of the viral capsid structure.

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