Human papillomavirus type 18 E7 protein interacts with the centromere protein that is essential for chromosome segregation. Free

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Human papillomaviruses (HPVs) cause a variety of human diseases, most notably cancer of cervix, a disease responsible for at least 200,000 death per year all over the world. Over 100 different types of HPVs have been identified, and approximately 20 are specific for the lesions in the anogenital tract. The latter HPVs are divided into two groups; the low risk group such as HPV 6 and 11 that are associated with benign proliferative epithelial lesions, and the high risk group such as HPV 16 and 18 that are associated with malignant tumors. The HPV genome encodes two transforming genes, E6 and E7, both being consistently expressed in HPV-positive cervical carcinomas. However, the precise mechanism of carcinogenesis caused by the HPV transforming proteins has not been fully understood. To investigate the function of HPV 18 E7 protein, the yeast two hybrid screen method was used to isolate the cellular proteins that interact with the HPV 18 E7 protein. We isolated 11candidate genes of which products can interact with the HPV 18 E7 protein; 3 (Rb, p130, and Dna J protein) have been known to interact with the HPV E7 protein, while 8 were novel HPV E7-interacters newly found in this study. One of the 8 proteins was a centromere protein, one of the components of the kinetocore complex. This protein interacted with the high risk HPV18 and 58 E7 proteins but not with the low risk HPV 4, 6 and 11 E7 proteins. The coimmunoprecipitation study demonstrated that the HPV 18 E7 protein could associate with the centromere protein in 293T cells in agreement with the yeast two-hybrid assay. Analysis using the deletion mutants showed that the CR1 region of HPV18 E7 protein and the C terminal region of the centromere protein were important for their interaction. We further investigated whether the binding of the HPV 18 E7 protein to the centromere protein may inhibit the binding of the centromere protein to α-satellaite DNA. To this end, 293T cells were co-transfected with the HA-tagged centromere protein cDNA and the HPV18 E7 cDNA, the DNA-centromere protein complex was immunoprecipitated using the anti-HA antibody, and α-satellite DNA was PCR-amplified using the primers specific for α-satellite DNA on chromosome 17 and X. This chromatin immunoprecipitation (ChIP) study revealed that the HPV18 E7 protein inhibits the binding of centromere protein to α-satellite DNA on chromosome 17 and X. Because the centromere proteins play an essential role in accurate chromosome segregation during mitosis and meiosis, and also because chromosome segregation errors can cause genetic alterations, we speculate that the binding of the HPV 18 E7 protein to the centromere protein may cause chromosomal abnormality, leading to tumorigenesis.