Multiple variants of HPV16 E6 gene in cervical invasive squamous cell carcinoma

Background: HPV16 is the most commonly detected genotype in cervical squamous cell carcinoma. E6 of HPV16 is a viral oncogene and has frequent DNA sequence variations whose encoded proteins have been shown to have heterogeneity in biochemical and biological properties. This study tried to establish whether the E6 variants derive from the infection pool or from spontaneous mutation in the host. Materials and Methods: We combined the use of microdissection of multiple areas of tumor tissue, PCR-sequencing of HPV16 E6 and E5 genes and allele-specific amplification of PCR to analyze the E6 variations in four cases of cervical cancer (M4, M12, M13 and M23). Results: We isolated two common (350G and 350T) and three rare (310G, 374T and 459C) E6 variations corresponding to five different E6 variants. The common E6 variations were always co-segregated with specific E5 variations. Both common variants persisted in all the four cases. Of three cases each had one additional rare E6 variant. Conclusion: The common E6 variants would derive from the infection pool, whereas the rare E6 variants may evolve from the mutation of either of the common E6 variants. This finding might have implications for the future study of natural HPV evolution, the design of viral vaccine and the carcinogenesis of cervical cancer.