Genetic variability of HPV-58 E6 and E7 genes in Southwest China

Abstract

HPV accounts for most of incidence of cervical cancer. Genetic variations of E6 and E7 may be associated with the development of cervical cancer in specific geographic regions. HPV-58 has been found to be a relatively prevalent high-risk HPV among southwest Chinese women. To explore gene intratypic variations and polymorphisms of HPV-58 E6 and E7 genes originating in Southwest China, a total of 2000 scraped cell samples were collected for DNA extraction and HPV typing. Then, the E6 and E7 genes of HPV-58 (n=22) were sequenced and compared to others submitted to GenBank, followed by an analysis of the diversity of secondary structure by DNASTAR software. Phylogenetic trees were then constructed by Neighbor-Joining and the Kimura 2-parameters methods, followed by an analysis of selection pressures acting on the E6/E7 genes by PAML software. 22 were HPV-58 positive among 215 high-risk types’ samples. The nucleotide variation rate of E6 was 86.36% (19/22) among the 22 HPV-58 E6 sequences studied. 4 single nucleotide changes were identified among the E6 sequences with 3/4 synonymous mutations (C187T, A260C, C307T) and 1/4 non-synonymous mutations (A388C, from Lys to Asn, in alpha helix). The most common mutations of E6 genes are the C307T and A388C. 8 single nucleotide changes were identified among the HPV-58 E7 sequences with 2/8 synonymous mutations (T726C, T744G) and 6/8 non-synonymous mutations (G599A, C632T, G694A, G760A, G761A, T803C). The nucleotide variation rate of E7 was 72.73% (17/22). The most common mutations of E7 genes are C632T, G694A, T744G, G760A (from Gly to Ser, in turn), G761A and T803C. The phylogenetic analyses demonstrate that all HPV-58 E6/E7 variants identified belonged to the Southeast Asia lineage. There was no evidence of positive selection in the sequence alignment of HPV-58 E6 and E7 genes.