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Short Communication |
1 Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY, USA
2 Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, USA
3 Proyecto Epidemiológico Guanacaste, Costa Rican Foundation for Health Sciences, San José, Costa Rica
4 Department of Pediatrics, Department of Epidemiology and Population Health, Department of Obstetrics, Gynecology and Woman's Health and Albert Einstein Cancer Center, Albert Einstein College of Medicine, Bronx, NY, USA
Correspondence
Robert D. Burk
burk{at}aecom.yu.edu
| ABSTRACT |
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3 and
15. HPV102 and HPV106 contain five early genes (E6, E7, E1, E2, and E4) and two late genes (L2 and L1), and both lack an E5 ORF. On the basis of phylogenetic analyses and available clinical information, these two novel HPV types expand the heterogeneity of HPVs detected in the lower genital tract. Location of the predicted ORFs of HPV102 and HPV106 and sequence of the primers used are available as supplementary material with the online version of this paper.
| MAIN TEXT |
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A phylogenetic tree of the alpha PVs based upon full genome alignments suggested that at least three ancestral PVs are responsible for the current heterogeneous group of genital HPV genomes (alpha PVs) (Schiffman et al., 2005
). Carcinogenic types, as defined at a recent workshop of the International Agency for Research on Cancer (IARC) (Cogliano et al., 2005
), include types limited to the alpha papillomavirus species
9,
11,
7,
5 and
6 that are derived from a common ancestor (Schiffman et al., 2005
), whereas genital HPV types derived from the other two ancestors appear to be non-pathogenic or have low oncogenic potential. In this report, two novel HPV types, HPV102 and HPV106, were identified, cloned and characterized. The L1 nucleotide sequence similarity by pairwise alignment indicated that HPV102 and HPV106 are closely related to HPV83 (genital HPV species
3) and HPV90 (genital HPV species
15), respectively.
Clinical specimens containing HPV102 and HPV106 originated from a 49-year-old Hispanic female with reactive changes on her Pap test and a 42-year-old Hispanic female with a Pap test diagnosis of atypical squamous cells of unknown significance (ASCUS), respectively. They were participating in a population-based HPV study in Costa Rica (Herrero et al., 2005
). HPV106 DNA was initially identified by PCR amplification with MY09/11 primers (Castle et al., 2002
), but did not hybridize to over 40 type-specific probes used in the HPV typing assays (Herrero et al., 2005
). HPV102 DNA was not amplified by MY09/MY11 PCR, but was positive by FAP primers within the L1 ORF (Forslund et al., 1999
). The 455 bp fragment amplified by MY09/MY11 primers from HPV106 and the 480 bp fragment amplified by the FAP primers from HPV102 were sequenced. A BLAST search against GenBank revealed that sequences of these MY and FAP fragments were 83 % related to HPV90 and 83 % related to HPV83, respectively. Thereafter, type-specific primer sets were designed based on available sequences and a consensus region within the E1 ORF for amplification of the complete genome in two fragments for HPV102 (4007 bp and 4453 bp) and three fragments for HPV106 (3980, 4006 and 412 bp). Oligonucleotide primer sequences used in this study are available from the authors. For overlapping PCR, an equal mixture of the AmpliTaq Gold Taq DNA polymerase (Applied Biosystems) and Pwo Platinum Taq DNA Polymerase (High Fidelity, Invitrogen) were utilized as previously described (Terai & Burk, 2001
).
For HPV cloning and sequencing, each PCR product was purified from agarose gel (Qiagen gel extraction kit) after confirmation of appropriate size, ligated into the pGEM-T easy vector (Promega) and sequenced by the Einstein Sequencing Facility, New York. Subsequent sequencing was performed using primer walking. The complete genomic sequences were determined from combined sets of sequences from overlapping amplification products. DNA clones were submitted to the Human Papillomavirus Reference Laboratory (Heidelberg, Germany) for official designation. The genome sequences of HPV102 and HPV106 were submitted to the NCBI/GenBank database (accession nos: HPV102, DQ080083; HPV106, DQ080082).
Phylogenetic trees were constructed to assess the position of HPV102 and HPV106 in relationship to other HPV types. MrBayes v3.0b4 (Huelsenbeck & Ronquist, 2001
) with 107 cycles for the Markov chain Monte Carlo (MCMC) algorithm was used to generate trees from the alignments of concatenated amino acid and nucleotide sequences of early (E6, E7, E1, E2 and E4) and late (L2 and L1) ORFs from closely related representative HPV types, respectively. Sequence alignments were prepared with computer programs CLUSTAL_X software (Thompson et al., 1997
) and Codon Align (ver 1.0) (available from website http://www.sinauer.com/hall/), as previously described (Chen et al., 2007
). For Bayesian tree construction, the gamma model was set for among-site rate variation, and allowed all substitution rates of aligned sequences to be different. Maximum-parsimony (MP) and neighbour-joining (NJ) trees were calculated by a heuristic search in PAUP* v4.0b10 (Swofford, 1998
). For maximum-parsimony analyses, amino acid and nucleotide sequences were reduced to phylogenetically informative sites. Data were bootstrap resampled 1000 times. Sequences of related PVs analysed in this work are available from the NCBI database.
A computational algorithm to test the incongruence length difference (ILD) was used to assess the relative degrees of incongruence across different node/partition pairs (Narechania et al., 2005
). The partition homogeneity test employed in the PAUP* v4.0b10 (Swofford, 1998
) was performed by treating early and late genes as separate partitions. The ILD values were calculated.
HPV species were generally classified according to de Villiers et al. (2004)
. However, we group HPV71 and HPV90 into the
15 species based on nucleotide similarities as previously described (Narechania et al., 2005
; Schiffman et al., 2005
).
The two HPV genomes were characterised by overlapping PCR. The complete nucleotide sequences of HPV102 and HPV106 contain 8078 and 8035 bp, with a G+C content of 45.3 and 46.9 mol%, respectively. The complete nucleotide sequences of HPV102 and HPV106 L1 ORFs share 84.1 % and 83.5 % similarity to HPV83 L1 (genital HPV species
3) and HPV90 L1 (
15), respectively. The nucleotide sequence of a small region of the HPV102 L1 ORF shares 99 % similarity with a previously reported MY09/11 PCR fragment, GA6053 (452 bp, GenBank accession no. Y11911) (Astori et al., 1997
).
To determine whether the two genomes showed similar degrees of similarity across different regions of their genomes, ratios of relatedness were calculated. The ratio of relatedness of the complete L1:E1 ORFs, using the pairwise similarity of nucleotide sequences of representative HPV types within species
3 and
15, is shown in Table 1
. These ratios provide evidence for a similar degree of relatedness across the genomes of species
3 and
15. The L1:E1 ratios of HPV102 and HPV106 compared with related types within the same species are near 1.0 (on average 0.980 and 0.953, respectively), consistent with the L1 ORF being one of the most conserved regions (Terai & Burk, 2002
). However, there is a 5' ORF in-frame with the predicted amino terminus of the HPV102 L1 ORF (nt 5353–5784, 432 bp) and the HPV106 L1 ORF (nt 5599–5781, 183 bp) (Supplementary Figure S1, available with the online version of this paper). These sequences overlap the carboxyl terminus of the L2 ORFs and potentially encode amino acids not related to the canonical L1 genes of HPV types within species
3 and
15. Therefore, we do not believe these additional 5' sequences are encoded since there is a consensus translation initiation codon for the L1 ORFs.
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The first ATG of the E6 ORF was defined as the first position of the complete genomes of HPV102 and HPV106. The putative E6 ORFs of HPV102 and HPV106 contain two zinc-binding domains CxxC(x)29CxxC, separated by 36 aa. The putative E7 ORFs of HPV102 and HPV106 contain one conserved zinc binding domain, CxxC(x)29CxxC, and a motif (LxCxE) for binding to the pRB protein. The ATP-binding site of the ATP-dependent helicase (GPSDTGKS for HPV102, GPADTGKS for HPV106) is conserved in the carboxy-terminal region of E1. The E4 ORF contains a start codon and overlaps the E2 ORF. A polyadenylation consensus sequence (AATAAA) for processing of early viral mRNA transcripts is present at the beginning of the L2 gene. The major (L1) and minor (L2) capsid proteins of both types show a nuclear localization signal at their 3' end.
The upstream regulatory regions (URRs) located between the stop codon of L1 and the first start codon of the E6 ORF of HPV102 and HPV106 consist of 782 and 733 bp, respectively, and contain many cis-acting regulatory sequences that control viral transcription and replication. Analysis of the HPV102 URR revealed four typical palindromic E2-binding sites [ACC(N)6GGT] at nt 7569–7580, 7608–7619, 7934–7945 and 8014–8025. Analysis also revealed three typical palindromic E2-binding sites (nt 7592–7603, 7939–7950 and 8015–8026) and a highly-related E2-binding site (nt 7872–7883) within the URR of HPV106. Multiple binding sites for transcriptional regulatory factors such as AP-1 (Chan et al., 1990
), NF-1 (Apt et al., 1993
), SP-1 (Gloss & Bernard, 1990
), transcriptional enhancer factors (TEF)-1 (Ishiji et al., 1992
) and YY-1 (Dong et al., 1994
) are also present within the URR regions.
To investigate the relationships between these two novel types and related HPV genomes, phylogenetic trees were constructed and compared based on the concatenated amino acid and nucleotide sequences of early (E6, E7, E1, E2 and E4) and late (L2 and L1) ORFs. Representative HPV types within species
2,
3,
4 and
15 were used to calculate Bayesian trees (Fig. 1
). HPV32 and HPV42 within the species
1 were set as the referent outgroup. Both early and late trees indicated that HPV102 and HPV106 were most closely related to HPV83 and HPV90, and were placed into genital HPV species
3 and
15, respectively. The MP and NJ trees also demonstrated stable and consistent topological positions for HPV102 and HPV106 like that in the Bayesian tree (data not shown). However, the ILD test detected significant incongruent evolutionary patterns between the early ORF and late ORF trees, as shown in Fig. 1
(P=0.007). In the early ORF tree, the
3 species forms a sister group to the clade consisting of species
2,
4 and
15, while the late ORF tree indicated the close relationship between species
3 and
4. The incongruence in the genital HPV phylogeny could reflect different evolutionary histories or evolutionary pressures among different genes (Narechania et al., 2005
).
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9) was the most common oncogenic type (3.6 % prevalence), while HPV61 (
3) and HPV71 (
15) were the most common non-oncogenic types (2.4 and 2.4 % prevalence, respectively). However, HPV102 and HPV106 appear to be rare in the female genital tract. HPV102 was identified in 4/7125 samples, and HPV106 was identified in 1/1993 samples. However, these estimates of prevalence are the lower limit of detectability, since the PCR systems have not been optimized for detection of HPV102 and HPV106. On the basis of phylogenetic analyses and available clinical information, these two novel HPV types expand the heterogeneity of HPVs detected in the lower genital tract.
| ACKNOWLEDGEMENTS |
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Received 21 May 2007;
accepted 10 July 2007.
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