Transcriptional activity of the long control region in human papillomavirus type 33 intratype variants

BACKGROUND: High-risk human papillomaviruses (HPVs) are responsible for the development of cervical and other anogenital cancers. Intratype sequence variants of certain high-risk HPV types (e.g. 16, 18 and 31) are thought to have different oncogenic potential, partly due to nucleotide sequence variation in the viral long control region (LCR). The LCR has an important role in the regulation of viral replication and transcription. The purpose of this study was to explore sequence variation in the LCR of HPV 33 intratype variants in Hungary and to see whether there are differences in the transcriptional activities of the variants. METHODS: The complete HPV 33 LCR was amplified from HPV 33 positive cervical samples. After sequencing the LCR variants, multiple sequence alignment and phylogenetic analyses were carried out. Representative HPV 33 LCR sequence variants were selected for cloning and functional analysis. After transient transfection of HeLa cells, luciferase reporter assays were used to analyse the transcriptional activities of different LCR variants. RESULTS: Altogether 10 different variants were identified by sequence analysis of the HPV 33 LCR. The results of phylogenetic analysis showed that 3 variants belonged to sublineage A1, while the other 7 variants clustered with sublineage A2. Variants belonging to sublineage A2 had significantly lower transcriptional activities than variants belonging to sublineage A1. Within sublineage A2, the two variants analysed had significantly different transcriptional activities, which was shown to be caused by the A7879G variation. CONCLUSIONS: Nucleotide variation in the HPV 33 LCR can result in altered transcriptional activity of the intratype variants. Our results can help to understand the correlation between LCR polymorphism and the oncogenic potential of HPV 33 variants.