Polymorphism in the E6 gene of human papillomavirus type 16 in the cervical tissues of Korean women

Human papillomavirus as a driver of head and neck cancers

The human papillomavirus (HPV) family includes more than 170 different types of virus that infect stratified epithelium. High-risk HPV is well established as the primary cause of cervical cancer, but in recent years, a clear role for this virus in other malignancies is also emerging. Indeed, HPV plays a pathogenic role in a subset of head and neck cancers-mostly cancers of the oropharynx-with distinct epidemiological, clinical and molecular characteristics compared with head and neck cancers not caused by HPV. This review summarises our current understanding of HPV in these cancers, specifically detailing HPV infection in head and neck cancers within different racial/ethnic subpopulations, and the differences in various aspects of these diseases between women and men. Finally, we provide an outlook for this disease, in terms of clinical management, and consider the issues of 'diagnostic biomarkers' and targeted therapies.

Human Papillomavirus Genotypes and HPV16 E6/E7 Variants among Patients with Genital Cancers in Vietnam

We previously reported human papillomavirus type 52 (HPV52) as the most prevalent high-risk genotype in non-cancer individuals in Vietnam. This study aimed to evaluate HPV genotypes and HPV16 E6 and E7 (E6/E7) gene variations in Vietnamese patients with genital cancers. Biopsy samples were collected from 124 Vietnamese patients with genital cancers (20 with vaginal, 50 with vulvar, and 54 with penile cancer). The HPV-DNA was amplified and genotyped, and HPV16 E6/E7 genes were compared with those previously reported for women with normal cervical cytology (N = 23). HPV-DNA was detected in 80.6% (100/124) of the cancer patients (80.0% of vaginal, 82.0% of vulvar, and 79.6% of penile), with HPV16/18 in 86.0% (86/100) and HPV52 in 7.0% (7/100) of the HPV-positive samples. The HPV-DNA prevalence and HPV genotype distribution did not significantly differ among the genital cancer patients (both P = 0.95). Significantly fewer instances of the HPV16 A4 sublineage (34.8% vs. 82.6%, P < 0.0001) and HPV16 E7 29S (36.4% vs. 87.0%, P = 0.0002) occurred in the cancer patients than in the women with normal cytology. Our results indicate that HPV16/18 accounts for more than 85% of genital cancers in Vietnam, and the HPV16 sublineage A4 containing E7 29S may be less oncogenic.

Human papillomavirus genome variants and head and neck cancers: a perspective

Human papillomaviruses (HPV) cause infections that are responsible for diverse clinical manifestations from benign conditions to invasive cancer. As different HPV types are associated with variable pathogenic potential, minor genetic variations within a given high-risk HPV type might also be associated with distinct oncogenic capacities, through variable ability of persistence or risk of progression to precancer/cancer. Most recent HPV variant studies in the cervix using latest sequencing technology confirmed that minor changes in the HPV genome can have a major influence on carcinogenesis and have revealed key data that help better understand the carcinogenicity of HPV at a molecular level. Here we review the limited number of studies on HPV genome variants in head and neck cancers (HNC) and discuss their implications for cancer research in the light of accumulated knowledge for the cervix. Challenges in transposing HPV variant studies from the lower anogenital to the upper aerodigestive tract are also discussed, highlighting the main gaps of knowledge in the field of HPV-induced HNC. Specifically in the head and neck region, the lack of characterisation of precancerous lesions and the difficulty in sampling normal tissue will challenge the development of accurate studies. Although there is so far no indication that HPV variant research in HNC could directly translate into clinical application, such research is expected to be useful to disentangle unanswered questions in the pathogenesis of HNC. Yet, history of HPV variant research suggests that, to be successful, studies will require large international collaborative efforts.

Association of human papillomavirus type 16 and its genetic variants with cervical lesion in Korea

Persistent human papillomavirus type 16 (HPV16) is the major risk factor for cervical cancer. HPV16 intratypic variants differ in their geographical distribution and oncogenic potential. This study aimed to analyze the distribution of HPV16 variants and their association with cervical lesion histopathology in Korean women. In total, 133 HPV16-positive cervical samples from women admitted to Seoul National University Boramae Hospital were analyzed by sequencing E6, E7, and L1 genes and the long control region (LCR), and the variant distribution according to cervical lesion grade was determined. Isolates were grouped into a phylogenetic lineage, and A1-3, A4, C, and D sublineages were detected in 54.1, 37.8, 0.7, and 7.4% of samples, respectively. The most commonly observed LCR variations were 7521G>A (91.5%), 7730A>C (59.6%), and 7842G>A (59.6%). Furthermore, A4 or D sublineage-positive women had a higher risk for cervical cancer than women who were positive for A1-3. Among HPV phylogenetic clusters, A1-3 was the predominant sublineage, and within A1-3, the 350G polymorphism was highly frequent. These results differed from those of previous studies in Korea and other Asian countries. The findings suggest that cervical neoplasia incidence in HPV16-infected patients could be affected by the distribution of HPV16 variants in the population.

Analysis of human papillomavirus 16 variants and risk for cervical cancer in Chinese population

HPV16 is the most carcinogenic HPV type, but only a minority of HPV16 infections progress to cancer. Intratype genetic variants of HPV16 have been suggested to confer differential carcinogenicity. To investigate risk implications of HPV16 variants among Chinese women, a case-control study was conducted with 298 cervical cancer patients and 85 controls (all HPV16-positive). HPV16 isolates were predominantly of the A variant lineage, and variants of A4 (previously named "Asian") sublineage were common. A4/Asian variants were significantly associated with increased risk of cervical cancer compared to A1-3 (OR=1.72, 95% CI=1.04-2.85). Furthermore, a meta-analysis including 703 cases and 323 controls from East Asia confirmed the association (OR=2.82, 95% CI=1.44-5.52). In conclusion, A4 variants appear to predict higher risk of cervical cancer among HPV16-positive women, which may provide clues to the genetic basis of differences in the carcinogenicity of HPV16 variants.

Intratypic variants of human papillomavirus type 16 and risk of cervical neoplasia in Taiwan

The associations between variants of human papillomavirus (HPV) 16 and risk of cervical neoplasia have been reported, but nucleotide variations of HPV 16 in Asian populations and their association with cervical neoplasia have not been evaluated extensively. During 1991-1992, 11,923 women from seven townships in Taiwan were enrolled. The HPV DNA in cervical cells was detected and genotyped using EasyChip HPV blot. Nucleotide variations in the long control region (LCR), E6, and E7 genes were determined using DNA sequencing for 170 HPV 16-positive cervical samples. The Asian variant was the most prevalent variant (81.8%) of HPV 16 in Taiwan, and was also associated with increased prevalence of histologically confirmed cervical intraepithelial neoplasia grade 3 or worse, showing an age-adjusted odds ratio (exact confidence limits) of 10.70 (1.62-451.05; P = 0.0049) compared to the HPV 16 European variant. Similar significant associations with cervical intraepithelial neoplasia grade 3 or worse were also observed for distinct nucleotide substitutions, including T178A/G, A647G, A7730C/G, T7781C, G7842A, and C24T/G. These results demonstrate that non-European variants (non-E) of HPV 16, predominantly Asian variants, are associated with increased risk for severe cervical neoplasia, compared with European variants. Molecular mechanisms accounting for varied cervical neoplasia risk among different HPV 16 variants warrant further investigation.

Long-term follow-up of HPV16-positive women: persistence of the same genetic variant and low prevalence of variant co-infections

HPV16 variants correlate with geographic origin and ethnicity. The association between infection with a specific variant and the cervical disease risk remains unclear. We studied the prevalence, persistence and association with cervical intraepithelial neoplasia (CIN) of different HPV16 variants, using cervical swabs and whole tissue sections (WTS) of biopsies from 548 women in the placebo group of a HPV16/18 vaccine trial. In HPV16-positive samples, HPV16 variants were identified by a reverse hybridization assay (RHA). Laser-capture micro-dissection (LCM) was performed for localized detection of HPV. HPV16 variants were determined in 47 women. Frequency of mixed HPV16 variant infections was lower (8.5%) than for multiple HPV genotypes (39.1%). Among 35 women having consecutive HPV16 variant-positive swabs, 32 (91.4%) had the same variant while in three (8.6%) women a change in variant(s) was observed. HPV16-positive WTS were obtained from 12 women having consecutive HPV16 variant-positive swabs. The same variant was present in WTS of 10 women, while two were negative. WTS of five women were histologically normal. A single HPV16 variant was detected in four women having CIN1-3, while additional HPV genotypes were found in three other women having CIN2 and CIN3. In the WTS of one woman with mixed genotypes, the HPV16 variant was assigned to a CIN2 lesion by LCM. HPV16 variant infections can be effectively studied in cervical swabs and tissue specimens by the HPV16 variant RHA. Multiple HPV16 variants in one woman are rare. The HPV16 genotype consistently detected in follow-up samples usually involves a persistent infection with the same variant.

Degradation of p53 by natural variants of the E6 protein of human papillomavirus type 16

The degradation of p53 by high-risk human papillomavirus (HR-HPV) E6 proteins is recognized as necessary for the immortalization of mammary epithelial cells and the progression of cancer. The HR-HPV type 16 E6 proteins exhibit numerous variants associated with different risk factors for the development of cervical cancer. Two variants of E6 proteins, D25E and L83V, are common in cervical carcinomas among Asian and European populations. In the present study, we compared the effect of two E6 variants on p53 degradation by a prototype E6 protein. We demonstrate that both the D25E and L83V variants downregulate p53 through a ubiquitin-proteasome pathway, and that the effect is very similar to that of the prototype E6 protein. The reduction in the p53 protein levels was induced through the ubiquitin-proteasome pathway via interaction with E6 proteins. The expression of p21 CIP1/WAF1, a downstream molecule of p53, was similarly reduced in both prototype and variant E6 protein-expressing cell lines, leading to aberrant G1/S cell cycle arrest. These results suggest that the natural variants, E6 D25E and L83V, similar to the prototype E6 protein, contribute to tumorigenesis by degrading p53.

HPV16 genetic variation and the development of cervical cancer worldwide

BACKGROUND

Factors that favour a small proportion of HPV16 infections to progress to cancer are still poorly understood, but several studies have implicated a role of HPV16 genetic variation.

METHODS

To evaluate the association between HPV16 genetic variants and cervical cancer risk, we designed a multicentre case-control study based on HPV16-positive cervical samples (1121 cervical cancer cases and 400 controls) from the International Agency for Research on Cancer biobank. By sequencing the E6 gene, HPV16 isolates were classified into variant lineages and the European (EUR)-lineage isolates were subclassified by the common polymorphism T350G.

RESULTS

Incidence of variant lineages differed between cases and controls in Europe/Central Asia (P=0.006, driven by an underrepresentation of African lineages in cases), and South/Central America (P=0.056, driven by an overrepresentation of Asian American/North American lineages in cases). EUR-350G isolates were significantly underrepresented in cervical cancer in East Asia (odds ratio (OR)=0.02 vs EUR-350T; 95% confidence interval (CI)=0.00-0.37) and Europe/Central Asia (OR=0.42; 95% CI=0.27-0.64), whereas the opposite was true in South/Central America (OR=4.69; 95% CI=2.07-10.66).

CONCLUSION

We observed that the distribution of HPV16 variants worldwide, and their relative risks for cervical cancer appear to be population-dependent.

Whole genome sequencing and evolutionary analysis of human papillomavirus type 16 in central China

Human papillomavirus type 16 plays a critical role in the neoplastic transformation of cervical cancers. Molecular variants of HPV16 existing in different ethnic groups have shown substantial phenotypic differences in pathogenicity, immunogenicity and tumorigenicity. In this study, we sequenced the entire HPV16 genome of 76 isolates originated from Anyang, central China. Phylogenetic analysis of these sequences identified two major variants of HPV16 in the Anyang area, namely the European prototype (E(p)) and the European Asian type (E(As)). These two variants show a high degree of divergence between groups, and the E(p) comprised higher genetic diversity than the E(As). Analysis with two measurements of genetic diversity indicated that viral population size was relatively stable in this area in the past. Codon based likelihood models revealed strong statistical support for adaptive evolution acting on the E6 gene. Bayesian analysis identified several important amino acid positions that may be driving adaptive selection in the HPV 16 population, including R10G, D25E, L83V, and E113D in the E6 gene. We hypothesize that the positive selection at these codons might be a contributing factor responsible for the phenotypic differences in carcinogenesis and immunogenicity among cervical cancers in China based on the potential roles of these molecular variants reported in other studies.

Gene expression profiles are altered in human papillomavirus-16 E6 D25E-expressing cell lines

Previously, we have reported that the human papillomavirus (HPV) type 16 E6 D25E is the most prevalent variant in Korean women at high risk for cervical cancers. Several studies have identified an association between the increased frequency of this variant and the elevated risk of cervical intraepithelial neoplasia and invasive cervical carcinoma. To investigate whether the HPV-16 E6 D25E variant might influence cervical cancer progression, we used an oligonucleotide microarray approach to identify transcriptionally altered gene expression patterns in recombinant wild-type E6 or E6 D25E variant-expressing HPV-negative cancer cells. We found that 211 genes were significantly up- or down-regulated (at least 1.5-fold, p < 0.05). We identified 14 genes, nine down-regulated and five up-regulated upon E6 D25E expression, compared with wild-type E6 expression. These results further emphasize the unique biological activity of the HPV-16 E6 D25E variant.

Distribution of human papillomavirus type 16 E6 and E7 gene variants in the progression of cervical dysplasia in Korean women

AIM

This cross-sectional, hospital-based study examined the distribution of human papillomavirus 16 E6 and E7 gene variants in Korean women with cervical lesions of varying degrees.

MATERIAL & METHODS

One hundred and forty-one Korean women (median age 43 years; range 22-65 years) with human papillomavirus 16 single infections were included. The human papillomavirus 16 E6/E7 sequences were amplified from cytology specimens. The distribution of human papillomavirus 16 variations with respect to cervical lesion was examined by the exact Mantel-Haenszel linear trend test (P(trend) ) and Fisher's exact test (P).

RESULTS

Human papillomavirus 16 E6 and E7 gene variants were identified in a total of 100 women (70.9%). The most prevalent human papillomavirus 16 variants were E6 Thymine178Guanine (number = 70, 49.6%) and E7 Adenine647Guanine (number = 75, 53.2%). Human papillomavirus 16 E6 Thymine178Guanine and E7 Adenine647Guanine were significantly related to the degree of cervical neoplasia (P(trend) = 0.0002, P< 0.0001; P(trend) < 0.0001, P < 0.0001, respectively). The odds ratio of human papillomavirus 16 E6 Thymine178Guanine to predict progression to cervical intraepithelial neoplasia 2-3 and invasive cancer was 2.37 (95% confidence interval 1.03-5.45) and 9.07 (95% confidence interval 2.86-28.72), respectively. The odds ratio of E7 Adenine647Guanine to predict progression to cervical intraepithelial neoplasia 2-3 and invasive cancer was 3.65 (95% confidence interval 1.16-8.51) and 9.07 (95% confidence interval 2.86-28.72), respectively.

CONCLUSION

The distribution of HPV variants appears to be related to geographic difference. Human papillomavirus 16 E6 Thymine178Guanine and E7 Adenine647Guanine can be used as the candidate marker for the progression of the cervical neoplasia.

Human papillomavirus (HPV) genotypes and HPV16 variants and risk of adenocarcinoma and squamous cell carcinoma of the cervix

OBJECTIVE

Human papillomavirus (HPV) genotypes have been extensively studied in uterine cervix squamous cell carcinoma and HPV16 variants have been found to be associated with increased cancer risk, but few reports have been published on genotype distribution and HPV16 variant prevalence in adenocarcinoma tumors. The objective of this study was to analyze viral genotypes and HPV16 intratypic variants in cervical adenocarcinoma and squamous cell carcinoma of Italian women.

METHODS

A total of 39 invasive adenocarcinoma and 132 squamous cell carcinoma were reviewed and classified according to the modified WHO classification. HPV sequences were detected by nested PCR, using the broad spectrum consensus-primer pairs MY09/MY11 and the GP5+/GP6+ system, and genotyped by nucleotide sequence analysis. The HPV16-positive cases were amplified with E6-specific oligonucleotides and amplimers subjected to direct nucleotide sequence for variant identification.

RESULTS

The prevalence rate of any HPV infection was 72% in adenocarcinoma, and 85% in cervical squamous cell carcinoma. Among the 140 HPV-positive cancer cases, a total of nine mucosal HPV genotypes (HPV16, 18, 31, 33, 35, 39, 45, 58, 82) epidemiologically classified as carcinogenic or probably carcinogenic viruses were identified. The HPV type 16 was the most common viral type representing 64% and 73% of all infections in adenocarcinoma and squamous cell carcinoma, respectively. The E6 nucleotide sequence analysis of HPV16 isolates allowed the identification of Asian American (AA) variants in 33% of adenocarcinoma and in 20% of squamous cell carcinoma suggesting their stronger association with cancer of glandular origin.

CONCLUSION

These results suggest that HPV16 has a high prevalence in both invasive adenocarcinoma and squamous cell carcinoma from Italian patients. Moreover this study confirms previous observations, summarized in a systematic review of the literature, on the increased cancer risk of HPV16 AA class in adenoglandular cancer, possibly related to their more oncogenic behavior compared to HPV16 European variants.

E6 molecular variants of human papillomavirus (HPV) type 16: an updated and unified criterion for clustering and nomenclature

Reports on taxonomic identification of E6/HPV 16 variants, don't have a worldwide, updated and unified criterion for clustering and nomenclature. Our aim was to update the existing criterion and propose a new one for clustering and nomenclature for E6/HPV 16 molecular variants based on the descriptive and comparative analyses of nucleotide sequences. A systematic search of the publications between 1991 and 2010 was carried out in PUBMED and manually. 240 E6/HPV 16 variants were identified. 157 were classified as European (E), 24 as Asian (As), 14 as Asian American (AA), 11 as North American 1 (NA 1), 19 as African 1 (Af 1) and 15 as African 2 (Af 2). Three classes were determined for the E, 3 each for the As, Af 2 and AA branches, 4 classes for the NA 1 and 6 for the Af 1 branch. This study reports our results and proposes an updated criterion for clustering and nomenclature that will be useful for E6 variant identification.

Human papillomavirus type 16 e6 gene variations in young Chinese women with cervical squamous cell carcinoma

Human papillomavirus (HPV) 16 E6 gene mutation is considered an important genetic change in cervical lesion progression. To explore the possible association of specific HPV16 E6 sequence variations with the development of invasive cervical squamous cell carcinoma (SCC) in young women, we examined the distribution of HPV16 E6 variants in a Chinese cervical SCC population and analyzed the difference between younger patients (≤35 years, n = 50) and older ones (>35ys, n = 71). Human papillomavirus type 16 E6 DNA was amplified by polymerase chain reaction and sequenced by Sanger fluorescent dye dideoxy-termination method. Analysis revealed that the most frequently found variation in this Chinese population was the EV (As) lineage (65.45%). In addition, the EV (As) lineage seems more common and uniform in younger patients than other lineages, and it may be associated with early age at diagnosis of cervical SCC in young women.

Increased risk for cervical disease progression of French women infected with the human papillomavirus type 16 E6-350G variant

To test the significance of human papillomavirus (HPV) type 16 and HPV16 E6 variants as risk factors for viral persistence and progression to high-grade lesion, we did a nested case-control study within a cohort study of >15,000 Caucasian French women. Three groups infected with high-risk HPV were compared: (a) women with cleared infection (controls, n = 201), (b) women with persistent infection (cases, n = 87), and (c) women who progressed into high-grade lesion (cases, n = 58). Women with persistent HPV infection and those that progressed into high-grade lesions were likelier to harbor HPV16 than other high-risk HPV types [odds ratio (OR), 2.4; 95% confidence interval (95% CI), 1.3-4.3 and OR, 4.2; 95% CI, 2.2-8.1, respectively]. Notably, especially elevated ORs of persistence (3.0; 95% CI, 1.4-6.7) and progression (6.2; 95% CI, 2.7-14.3) were found among women who harbored the HPV16 350G variant. Thus, HPV type and HPV16 variant seem to be risk factors for viral persistence and progression of infections into high-grade cervical lesions.

Epidemiological and functional implications of molecular variants of human papillomavirus

Human papillomavirus genomes are classified into molecular variants when they present more than 98% of similarity to the prototype sequence within the L1 gene. Comparative nucleotide sequence analyses of these viruses have elucidated some features of their phylogenetic relationship. In addition, human papillomavirus intratype variability has also been used as an important tool in epidemiological studies of viral transmission, persistence and progression to clinically relevant cervical lesions. Until the present, little has been published concerning the functional significance of molecular variants. It has been shown that nucleotide variability within the long control region leads to differences in the binding affinity of some cellular transcriptional factors and to the enhancement of the expression of E6 and E7 oncogenes. Furthermore, in vivo and in vitro studies revealed differences in E6 and E7 biochemical and biological properties among molecular variants. Nevertheless, further correlation with additional functional information is needed to evaluate the significance of genome intratypic variability. These results are also important for the development of vaccines and to determine the extent to which immunization with L1 virus-like particles of one variant could induce antibodies that cross-neutralize other variants.

Analysis of mutations in the E6/E7 oncogenes and L1 gene of human papillomavirus 16 cervical cancer isolates from China

Human papillomavirus type 16 (HPV16) has a number of intratypic variants; each has a different geographical distribution and some are associated with enhanced oncogenic potential. Cervical samples were collected from 223 cervical cancer patients and from 196 age-matched control subjects in China. DNA samples were amplified by using primers specific for the E6, E7 and partial L1 regions. Products were sequenced and analysed. It was found by using a PCR-sequence-based typing method that HPV infection rates in China were 92.8 % in cervical cancer patients and 15.8 % in healthy controls. HPV16 was detected in 70.4 % of cervical cancer patients and in 6.1 % of controls. In HPV16-positive cervical cancers, 23.6 % belonged to the prototype, 65.5 % were of the Asian variant, 5.5 % were of African type 1 and 3.6 % were European variants, whilst only one was a new variant that differed from any variant published so far. Prevalences of HPV16 E6 D25E and E113D variants were 67.3 and 9 %, respectively. In addition to D25E and E113D, the following E6 variations were found in this study: R129K, E89Q, S138C, H78Y, L83V and F69L. The results also showed that the prevalences of three hot spots of E7 nucleotide variation, N29S, S63F and a silent variation, nt T846C, were 70.2 % (33/47), 51.1 % (24/47) and 61.7 % (29/47), respectively. The following L1 variations were found in this study: S377A, K387E, E378D, K382E and T379P. It was also found that the average age of Asian variant-positive cervical cancer patients (42.98+/-10.43 years) was 7.56 years lower than that of prototype-positive patients (50.54+/-10.91). It is suggested that the high frequency of HPV16 Asian variants might contribute to the high incidence of cervical cancer in China.