Non-Random Integration of the HPV Genome in Cervical Cancer

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

Differences in Stability of Viral and Viral-Cellular Fusion Transcripts in HPV-Induced Cervical Cancers

HPV-DNA integration results in dysregulation of viral oncogene expression. Because viral-cellular fusion transcripts inherently lack the viral AU-rich elements of the 3’UTR, they are considered to be more stable than episome-derived transcripts. The aim of this study is to provide formal proof for this assumption by comparing the stability of viral early transcripts derived from episomal and integrated HPV16 DNA, respectively. Full-length cDNA of three fusion transcripts comprising viral and cellular sequences in sense orientation were amplified and cloned into the adeno-viral-vector pAd/CMV/V5-DEST. The most abundant HPV16 oncogene transcript E6*I-E7-E1vE4-E5 with and without 3’UTR, served as reference and control, respectively. Human primary keratinocytes were transduced using high titer virus stocks. qRT-PCR was performed to determine mRNA stability in relation to GAPDH in the presence of actinomycin-D. In four independent transduction experiments, all three viral-cellular fusion transcripts were significantly more stable compared to the episome-derived reference. Among the three viral-cellular fusion transcripts the most stable transcript was devoid of the instability core motif “AUUUA”. Unexpectedly, there was no significant difference in the stability between the episome-derived transcripts either with or without 3’UTR, indicating that the AU-rich elements of the 3’UTR are not contributing to RNA stability. Instead, the three “AUUUA” motifs located in the untranslated region between the viral E4 and E5 genes may be responsible for the instability. This is the first report showing that authentic viral-cellular fusion transcripts are more stable than episome-derived transcripts. The longer half-life of the fusion transcripts may result in increased levels of viral oncoproteins and thereby drive the carcinogenic process

Überblick Literaturverwaltung

Vorlesungsfolien zu den ThULB-Schulungen "Überblick Literaturverwaltung", gehalten zuletzt im Dezember 2015

Überblick Literaturverwaltung

Vorlesungsfolien zu den ThULB-Schulungen "Überblick Literaturverwaltung", gehalten zuletzt im Januar 2015

Sequence homologies between the HPV16 genome and the two adjoining genes <i>TP63</i> and <i>LEPREL1</i>.

<p>Three homologous stretches of up to 50 nucleotides are shown. The number of exact nucleotide matches is given in brackets (see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0039632#pone.0039632.s001" target="_blank">Sequences S1</a>). The DNA loop between the two homologies located on <i>LEPREL1</i> comprises 102.689 nucleotides; the second loop 269.968 nucleotides. Grey dots refer to the approximate location of the corresponding viral-cellular fusion transcripts detected in tumors D3829, T2107 and T4335 (from left to right).</p

Genes affected by HPV integration at least twice in individual tumors.

‡<p>n.s.: not specified; n.a.: not applicable, because fusion transcript is in antisense orientation; ^†integration sites without reference result from this work.</p>1<p>Two fusion transcripts were found in T2107; ²refers to sequenced integration sites; ³TP73L alias TP63; ⁴<i>sweeker</i> in Kraus 2008 is no longer listed in any database; ⁵VMP1 alias TMEM49; ⁶DKFZP566I133 alias TMEM49.</p

Summary of all viral-cellular fusion transcripts analysed.

1<p>Common and rare fragile sites located at a distance of up to 5 Mb adjacent to the integration locus. Rare fragile sites are shown in italics.</p>‡<p>n.a.: not applicable, because fusion transcript is in antisense orientation.</p

Differences in Stability of Viral and Viral-Cellular Fusion Transcripts in HPV-Induced Cervical Cancers

HPV-DNA integration results in dysregulation of viral oncogene expression. Because viral-cellular fusion transcripts inherently lack the viral AU-rich elements of the 3&rsquo;UTR, they are considered to be more stable than episome-derived transcripts. The aim of this study is to provide formal proof for this assumption by comparing the stability of viral early transcripts derived from episomal and integrated HPV16 DNA, respectively. Full-length cDNA of three fusion transcripts comprising viral and cellular sequences in sense orientation were amplified and cloned into the adeno-viral-vector pAd/CMV/V5-DEST. The most abundant HPV16 oncogene transcript E6*I-E7-E1vE4-E5 with and without 3&rsquo;UTR, served as reference and control, respectively. Human primary keratinocytes were transduced using high titer virus stocks. qRT-PCR was performed to determine mRNA stability in relation to GAPDH in the presence of actinomycin-D. In four independent transduction experiments, all three viral-cellular fusion transcripts were significantly more stable compared to the episome-derived reference. Among the three viral-cellular fusion transcripts the most stable transcript was devoid of the instability core motif &ldquo;AUUUA&rdquo;. Unexpectedly, there was no significant difference in the stability between the episome-derived transcripts either with or without 3&rsquo;UTR, indicating that the AU-rich elements of the 3&rsquo;UTR are not contributing to RNA stability. Instead, the three &ldquo;AUUUA&rdquo; motifs located in the untranslated region between the viral E4 and E5 genes may be responsible for the instability. This is the first report showing that authentic viral-cellular fusion transcripts are more stable than episome-derived transcripts. The longer half-life of the fusion transcripts may result in increased levels of viral oncoproteins and thereby drive the carcinogenic process

Chromosomal hotspots for HPV integration.

<p>Depicted are integration sites located within the cytogenetic bands 3q28 (A), 4q13.3 (B), 8q24.21 (C), 13q22.1 (D) and 17q21.2 (E). Light blue arrows: genes affected by HPV integration; red arrows: HPV fusion transcripts described in this work; grey arrows: HPV fusion transcripts described by Kraus et al. 2008; green arrows: fragile site; dark blue arrows: microRNAs.</p