Abstract
HPV DNA integration into the host genome is a characteristic but not an exclusive step during cervical carcinogenesis. It is still a matter of debate whether viral integration contributes to the transformation process beyond ensuring the constitutive expression of the viral oncogenes. There is mounting evidence for a non-random distribution of integration loci and the direct involvement of cellular cancer-related genes. In this study we addressed this topic by extending the existing data set by an additional 47 HPV16 and HPV18 positive cervical carcinoma. We provide supportive evidence for previously defined integration hotspots and have revealed another cluster of integration sites within the cytogenetic band 3q28. Moreover, in the vicinity of these hotspots numerous microRNAs (miRNAs) are located and may be influenced by the integrated HPV DNA. By compiling our data and published reports 9 genes could be identified which were affected by HPV integration at least twice in independent tumors. In some tumors the viral-cellular fusion transcripts were even identical with respect to the viral donor and cellular acceptor sites used. However, the exact integration sites are likely to differ since none of the integration sites analysed thus far have shown more than a few nucleotides of homology between viral and host sequences. Therefore, DNA recombination involving large stretches of homology at the integration site can be ruled out. It is however intriguing that by sequence alignment several regions of the HPV16 genome were found to have highly homologous stretches of up to 50 nucleotides to the aforementioned genes and the integration hotspots. One common region of homologies with cellular sequences is between the viral gene E5 and L2 (nucleotides positions 4100 to 4240). We speculate that this and other regions of homology are involved in the integration process. Our observations suggest that targeted disruption, possibly also of critical cellular genes, by HPV integration remains an issue to be fully resolved.
Highlights
A persistent infection with high risk human papillomaviruses (HR-HPV) in particular HPV16 and 18 is recognized as the highest risk factor for the development of cervical cancer [1]
The viral cellular fusion transcripts could be assigned to all chromosomes, except for chromosome 11, 14, 16, 18 and 20 and are summarized in table 1
HPV integration into the host genome is likely to be a very frequent event but cannot be readily detected if integration occurs in a single cell without subsequent clonal selection pressure
Summary
A persistent infection with high risk human papillomaviruses (HR-HPV) in particular HPV16 and 18 is recognized as the highest risk factor for the development of cervical cancer [1]. Most HR-HPV infections are either latent or permissive. Virus replication in terms of virion production is confined to terminally differentiated cells of the intermediate and superficial epithelial layers and results from a switch of a latent to a permissive phase or directly from an acute infection. In an estimated 10% of cases a transforming type of HPV infection evolves. This transformation process is characterized by the deregulation of viral oncogenes E6 and E7 in cycling cells which results in chromosomal instability and the accumulation of mutations. The highest carcinogenic potential is ascribed to HPV16 and HPV18 [8]
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