Abstract

In previous studies, we firstly isolated a new human papillomavirus type 16 E7 variant (HBE7.16) from cervical cancer biopsies of patients from Wufeng County of Hubei Province, China, where the mortality rate of cervical cancer ranks the highest in China. We identified 2 mutations in HBE7.16 compared with the prototype E7 gene (E7.16). The more relevant mutation produces a termination codon, resulting in a truncated E7 protein containing 43 amino acids, making it about half the size of the wild-type. In this study, we investigated the biological function of this HBE7.16 protein. We compared the transforming potential of HBE7.16 to E7.16 in National Institute of Health (NIH) 3T3 cells using cell proliferation and anchorage-independent growth assays. We also examined the expression level of cdc25A, cyclin A, and cyclin E in transformed cells using semi-quantitative reverse transcription-polymerase chain reaction. The results showed that E7.16 and HBE7.16 significantly transform NIH3T3 cells, and HBE7.16 holds greater transforming activity than E7.16. Cells expressing HBE7.16 can more easily transit from G1 into S phase and express higher levels of cdc25A and cyclin A compared with E7.16. No significant difference in the expression level of cyclin E was seen. We propose that up-regulation of cdc25A and cyclin A contributes, at least partially, to E7.16- or HBE7.16-induced transformation of NIH 3T3 cells. In addition, higher transforming ability of HBE7.16 may be responsible for the increased mortality of cervical cancer in Wufeng County.