Human papillomavirus (HPV) type 18 induces extended growth in primary human cervical, tonsillar, or foreskin keratinocytes more effectively than other high-risk mucosal HPVs

Differential requirement of the transcription factor HOXC13 for the stable maintenance of human papillomavirus genome among high-risk genotypes

The viral genome of the high-risk human papillomavirus (HPV), the causative agent of cervical cancer, is stably maintained as extrachromosomal episomes that establish persistent infection. We previously identified homeobox-transcription factor HOXC13 as an important host protein mediating the short-term retention of the HPV16 and HPV18 genomes in normal human immortalized keratinocytes (NIKS). Here, we used CRISPR-Cas9 technology to construct HOXC13 knockout (KO) NIKS cells to determine whether HOXC13 is required for the long-term maintenance of high-risk HPV genomes. HPV16, HPV18, HPV52, and HPV58 whole genomes were transfected into HOXC13 KO cells, and the copy number of viral genomes per cell was monitored over cell passages. Copy numbers of HPV16, HPV52, and HPV58 genomes decreased continuously in HOXC13 KO cells, whereas HPV18 genomes remained stable throughout passages. Thus, HOXC13 is critical for the stable maintenance of the viral genomes of HPV16, HPV52, and HPV58, but not HPV18.

Mathematical Modeling and Computational Prediction of High-Risk Types of Human Papillomaviruses

Cervical cancer is one of the main causes of cancer death all over the world. Most diseases such as cervical epithelial atypical hyperplasia and invasive cervical cancer are closely related to the continuous infection of high-risk types of human papillomavirus. Therefore, the high-risk types of human papillomavirus are the key to the prevention and treatment of cervical cancer. With the accumulation of high-throughput and clinical data, the use of systematic and quantitative methods for mathematical modeling and computational prediction has become more and more important. This paper summarizes the mathematical models and prediction methods of the risk types of human papillomavirus, especially around the key steps such as feature extraction, feature selection, and prediction algorithms. We summarized and discussed the advantages and disadvantages of existing algorithms, which provides a theoretical basis for follow-up research.

Regulation of HPV18 Genome Replication, Establishment and Persistence by Sequences in the Viral Upstream Regulatory Region

During persistent human papillomavirus infection, the viral genome replicates as an extrachromosomal plasmid that is efficiently partitioned to daughter cells during cell division. We have previously shown that an element which overlaps the HPV18 transcriptional enhancer promotes stable DNA replication of replicons containing the viral replication origin. Here we perform comprehensive analyses to elucidate the function of this maintenance element. We conclude that no unique element or binding site in this region is absolutely required for persistent replication and partitioning, and instead propose that the overall chromatin architecture of this region is important to promote efficient use of the replication origin. These results have important implications on the genome partitioning mechanism of papillomaviruses. Importance Persistent infection with oncogenic HPVs is responsible for ∼5% human cancers. The viral DNA replicates as an extrachromosomal plasmid and is partitioned to daughter cells in dividing keratinocytes. Using a complementation assay that allows us to separate viral transcription and replication, we provide insight into viral sequences that are required for long term replication and persistence in keratinocytes. Understanding how viral genomes replicate persistently for such long periods of time will guide the development of anti-viral therapies.

E6/E7 Functional Differences among Two Natural Human Papillomavirus 18 Variants in Human Keratinocytes

It is suggested that HPV-18 variants from the A lineage have higher oncogenic potential compared to B variants. Some studies show uneven distribution of HPV-18 variants in cervical adenocarcinomas and squamous cell carcinomas. Regarding HPV-18 variants’ functions, the few studies reported focus on E6, and none were performed using natural host cells. Here, we immortalized primary human keratinocytes (PHKs) with E6/E7 of HPV-18 A1 and B1 sublineages and functionally characterized these cells. PHK18A1 reached immortalization significantly faster than PHK18B1 and formed a higher number of colonies in monolayer and 3D cultures. Moreover, PHK18A1 showed greater invasion ability and higher resistance to apoptosis induced by actinomycin-D. Nevertheless, no differences were observed regarding morphology, proliferation after immortalization, migration, or epithelial development in raft cultures. Noteworthy, our study highlights qualitative differences among HPV-18 A1 and B1 immortalized PHKs: in contrast to PHK18A1, which formed more compact colonies and spheroids of firmly grouped cells and tended to invade and migrate as clustered cells, morphologically, PHK18B1 colonies and spheroids were looser, and migration and invasion of single cells were observed. Although these observations may be relevant for the association of these variants with cervical cancer of different histological subtypes, further studies are warranted to elucidate the mechanisms behind these findings.

Cytokeratin 7 and 19 expression in oropharyngeal and oral squamous cell carcinoma

PURPOSE

The precise etiopathogenesis of human papillomavirus (HPV)-related oropharyngeal squamous cell carcinoma (OPSCC), and reasons for predilection for crypt epithelium, remain uncertain. The purpose of this study is to investigate the interaction between HPV and specific cytokeratins 7 (CK7) and 19 (CK19) in crypt epithelium.

METHODS

This is a retrospective cohort study of patients presenting between 1999 and 2015 at a tertiary referral center. CK7 and CK19 positivity and H Scores were determined by immunohistochemistry. Disease-specific and overall survival rates were analyzed.

RESULTS

There were 253 patients presenting with OPSCC (134), squamous cell carcinoma (SCC) of unknown primary site (22), and oral tongue SCC (97). Primary tumor CK7 and CK19 positivity and H Scores were significantly higher in HPV-positive OPSCC than HPV-negative OPSCC and oral tongue SCC. Higher CK19 Scores, but not CK7 Scores, were also seen in regional metastases from HPV-positive OPSCC than other sites. No impact on disease-specific or overall survival was identified on multivariate analysis.

CONCLUSION

The increased expression of CK7 and CK19 in HPV-positive OPSCC compared to HPV-negative disease supports the theory for a role for these cytokeratins in the etiopathogenesis of HPV-related OPSCC.

Modelling human papillomavirus biology in oropharyngeal keratinocytes

Most human papillomavirus (HPV) positive head and neck cancers arise in the tonsil crypts; deep invaginations at the tonsil surface that are lined with reticulated epithelium infiltrated by immune cells. As in cervical HPV infections, HPV16 is the most prevalent high-risk type in the oropharyngeal cancers, and a genital-oral route of infection is most likely. However, the natural history of HPV-driven oropharyngeal pathogenesis is an enigma, although there is evidence that it is different to that of cervical disease. It is not known if the virus establishes a productive or abortive infection in keratinocytes of the tonsil crypt, or if viral infections progress to cancer via a neoplastic phase, as in cervical HPV infection. The HPV DNA is more frequently found unintegrated in the cancers of the oropharynx compared to those that arise in the cervix, and may include novel HPV-human DNA hybrids episomes. Here, we review current understanding of HPV biology in the oropharynx and discuss the cell-based systems being used to model the HPV life cycle in tonsil keratinocytes and how they can be used to inform on HPV-driven neoplastic progression in the oropharynx.

This article is part of the theme issue ‘Silent cancer agents: multi-disciplinary modelling of human DNA oncoviruses’.

Characterization of an HPV33 natural variant with enhanced transcriptional activity suggests a role for C/EBPβ in the regulation of the viral early promoter

The Long Control Region (LCR) of the human papillomavirus (HPV) genome encompasses the early promoter (EP) that drives expression of the viral oncogenes in infected cells and HPV-associated cancers. Here, we report on a natural variant of HPV33 that displays higher EP activity than the prototype in transfected C33A and HeLa cervical carcinoma cells, and in the osteosarcoma U2OS cell line which supports replication of HPV episomes. This increased promoter activity was ascribed to a single nucleotide variation in the LCR, T7791C, in a putative binding site for the transcription factor C/EBPβ. T7791C abrogated binding of recombinant C/EBPβ to this site in vitro and stimulated the EP in vivo, suggesting that it abrogates a negatively-acting regulatory element. A second C/EBPβ binding site was identified in vitro that activated the EP in vivo and whose function and location in the epithelial-specific enhancer is shown to be conserved in the highly prevalent HPV18. These results suggest that C/EBPβ is both an activator and a repressor of the HPV33 EP, acting via two distinct binding sites. Prediction of C/EBPβ sites in the LCR of 186 HPV types suggests that C/EBPβ regulation of the EP is common among high‐risk viruses from the α genus.

Genetic variations in the DNA replication origins of human papillomavirus family correlate with their oncogenic potential

Human papillomaviruses (HPVs) encompass a large family of viruses that range from benign to highly carcinogenic. The crucial differences between benign and carcinogenic types of HPV remain unknown, except that the two HPV types differ in the frequency of DNA replication. We have systematically analyzed the mechanism of HPV DNA replication initiation in low-risk and high-risk HPVs. Our results demonstrate that HPV-encoded E2 initiator protein and its four binding sites in the replication origin play pivotal roles in determining the destiny of the HPV-infected cell. We have identified strain-specific single nucleotide variations in E2 binding sites found only in the high-risk HPVs. We have demonstrated that these variations result in attenuated formation of the E2-DNA complex. E2 binding to these sites is linked to the activation of the DNA replication origin as well as initiation of DNA replication. Both electrophoretic mobility shift assay and atomic force microscopy studies demonstrated that binding of E2 from either low- or high-risk HPVs with variant binding sequences lacked multimeric E2-DNA complex formation in vitro. These results provided a molecular basis of differential DNA replication in the two types of HPVs and pointed to a correlation with the development of cancer.

Use of a Rho kinase inhibitor to increase human tonsil keratinocyte longevity for three-dimensional, tissue engineered tonsil epithelium equivalents

The generation of tissue-engineered epithelial models is often hampered by the limited proliferative capacity of primary epithelial cells. This study aimed to isolate normal tonsillar keratinocytes (NTK) from human tonsils, increase the lifespan of these cells using the Rho kinase inhibitor Y-27632 and to develop tissue-engineered equivalents of healthy and infected tonsil epithelium. The proliferation rate of isolated NTK and expression of c-MYC and p16INK4A were measured in the absence or presence of the inhibitor. Y-27632-treated NTK were used to generate tissue-engineered tonsil epithelium equivalents using de-epidermised dermis that were then incubated with Streptococcus pyogenes to model bacterial tonsillitis, and the expression of pro-inflammatory cytokines was measured by cytokine array and ELISA. NTK cultured in the absence of Y-27632 rapidly senesced whereas cells cultured in the presence of this inhibitor proliferated for over 30 population doublings without changing their phenotype. Y-27632-treated NTK produced a multi-layered differentiated epithelium that histologically resembled normal tonsillar surface epithelium and responded to S. pyogenes infection by increased expression of pro-inflammatory cytokines including CXCL5 and IL-6. NTK can be isolated and successfully cultured in vitro with Y-27632 leading to a markedly prolonged lifespan without any deleterious consequences to cell morphology. This functional tissue-engineered equivalent of tonsil epithelium will provide a valuable tool for studying tonsil biology and host-pathogen interactions in a more physiologically relevant manner.

Novel recombinant papillomavirus genomes expressing selectable genes

Papillomaviruses infect and replicate in keratinocytes, but viral proteins are initially expressed at low levels and there is no effective and quantitative method to determine the efficiency of infection on a cell-to-cell basis. Here we describe human papillomavirus (HPV) genomes that express marker proteins (antibiotic resistance genes and Green Fluorescent Protein), and can be used to elucidate early stages in HPV infection of primary keratinocytes. To generate these recombinant genomes, the late region of the oncogenic HPV18 genome was replaced by CpG free marker genes. Insertion of these exogenous genes did not affect early replication, and had only minimal effects on early viral transcription. When introduced into primary keratinocytes, the recombinant marker genomes gave rise to drug-resistant keratinocyte colonies and cell lines, which maintained the extrachromosomal recombinant genome long-term. Furthermore, the HPV18 "marker" genomes could be packaged into viral particles (quasivirions) and used to infect primary human keratinocytes in culture. This resulted in the outgrowth of drug-resistant keratinocyte colonies containing replicating HPV18 genomes. In summary, we describe HPV18 marker genomes that can be used to quantitatively investigate many aspects of the viral life cycle.

Brd4 Activates Early Viral Transcription upon Human Papillomavirus 18 Infection of Primary Keratinocytes

Human papillomaviruses (HPVs) replicate in the cutaneous and mucosal epithelia, and the infectious cycle is synchronous with the differentiation program of the host keratinocytes. The virus initially infects dividing cells in the lower layers of the epithelium, where it establishes a persistent infection. The viral genome is maintained as a low-copy-number, extrachromosomal element in these proliferating cells but switches to the late stage of the life cycle in differentiated cells. The cellular chromatin adaptor protein Brd4 is involved in several stages and processes of the viral life cycle. In concert with the viral transcriptional regulator E2, Brd4 can repress transcription from the early viral promoter. Brd4 and E2 form a complex with the viral genome that associates with host chromosomes to partition the viral genome in dividing cells; Brd4 also localizes to active sites of productive HPV DNA replication. However, because of the difficulties in producing HPV viral particles, the role of Brd4 in modulating viral transcription and replication at the initial stage of infection is unclear. In this study, we have used an HPV18 quasivirus-based genome delivery system to assess the role of Brd4 in the initial infectivity of primary human keratinocytes. We show that, upon infection of primary human keratinocytes with HPV18 quasivirus, Brd4 activates viral transcription and replication. Furthermore, this activation is independent of the functional interaction between Brd4 and the HPV18 E2 protein.

HPVs lack encapsidated proteins and so rely exquisitely on host cellular factors to initiate their gene expression programs in newly infected cells. Brd4 is an important cellular chromatin adaptor molecule that normally activates host transcription initiation and elongation. In this study, we further optimize and utilize a quasivirus infection system to show that Brd4 activates HPV18 transcription at early stages of infection. HPVs are important human pathogens causing a wide range of cutaneous and tumorigenic morbidities. Therefore, specifically targeting this protein could provide a new target of therapeutic prevention of establishment of HPV infections.

Prognostic significance of non-HPV16 genotypes in oropharyngeal squamous cell carcinoma

OBJECTIVES

Recent studies have found that cases with oropharyngeal squamous cell carcinoma (OPSCC) positive for HPV16 genotype have better overall survival compared with cases positive for other HPV genotypes. We sought to further replicate these studies and determine if this relationship is modified by expression of p16 tumor suppressor protein.

MATERIAL AND METHODS

We identified 238 OPSCC cases from the Carolina Head and Neck Cancer Study (CHANCE) study, a population based case-control study. Tumors that tested positive solely for HPV16 genotype and no other genotypes with PCR were classified as HPV16-positive. Tumors positive for any other high-risk HPV genotype were classified as non-HPV16-positive. Expression of p16 in the tumor was determined with immunohistochemistry. Follow-up time was calculated from the date of diagnosis to date of death or December 31, 2013. Overall survival was compared with the Kaplan-Meier curves and log-rank test. Hazard ratios (HR) adjusted for smoking, alcohol use, sex, race, and age was calculated with the Cox proportional hazard regression.

RESULTS

Cases with HPV16-positive OPSCC had better overall survival than cases with non-HPV16-positive OPSCC (log-rank p-value: 0.010). When restricted to OPSCC cases positive for p16 expression, the same trend continued (log-rank p-value: 0.002). In the adjusted model, cases with non-HPV16-positive OPSCC had greater risk of death compared to cases with HPV16-positive tumors (HR: 1.92; 95% CI: 1.03, 3.60).

CONCLUSIONS

This finding indicates that HPV genotyping carries valuable prognostic significance in addition to p16 status and future survival studies of OPSCC should take into account differing HPV genotypes.

Comparison of the miRNA profiles in HPV-positive and HPV-negative tonsillar tumors and a model system of human keratinocyte clones

BACKGROUND

Better insights into the molecular changes involved in virus-associated and -independent head and neck cancer may advance our knowledge of HNC carcinogenesis and identify critical disease biomarkers. Here we aimed to characterize the expression profiles in a matched set of well-characterized HPV-dependent and HPV-independent tonsillar tumors and equivalent immortalized keratinocyte clones to define potential and clinically relevant biomarkers of HNC of different etiology.

METHODS

Fresh frozen tonsillar cancer tissues were analyzed together with non-malignant tonsillar tissues and compared with cervical tumors and normal cervical tissues. Furthermore, relative miRNAs abundance levels of primary and immortalized human keratinocyte clones were evaluated. The global quantitation of miRNA gene abundance was performed using a TaqMan Low Density Array system. The confirmation of differentially expressed miRNAs was performed on a set of formalin-fixed paraffin-embedded tumor samples enriched for the tumor cell fraction by macrodissection.

RESULTS

We defined 46 upregulated and 31 downregulated miRNAs characteristic for the HPV-positive tonsillar tumors and 42 upregulated miRNAs and 42 downregulated miRNAs characteristic for HPV-independent tumors. In comparison with the expression profiles in cervical tumors, we defined miR-141-3p, miR-15b-5p, miR-200a-3p, miR-302c-3p, and miR-9-5p as specific for HPV induced malignancies. MiR-335-5p, miR-579-3p, and miR-126-5p were shared by the expression profiles of HPV-positive tonsillar tumors and of the HPV immortalized keratinocyte clones, whereas miR-328-3p, miR-34c-3p, and miR-885-5p were shared by the miRNA profiles of HPV-negative tonsillar tumors and the HPV-negative keratinocytes.

CONCLUSIONS

We identified the miRNAs characteristic for HPV-induced tumors and tonsillar tumors of different etiology, and the results were compared with those of the model system. Our report presents the basis for further investigations leading to the identification of clinically relevant diagnostic and/or therapeutic biomarkers for tumors of viral and non-viral etiology.

Longitudinal assessment of DNA methylation changes during HPVE6E7-induced immortalization of primary keratinocytes

High-risk human papillomavirus (hrHPV)-induced immortalization and malignant transformation are accompanied by DNA methylation of host genes. To determine when methylation is established during cell immortalization and whether it is hrHPV-type dependent, DNA methylation was studied in a large panel of HPVE6E7-immortalized keratinocyte cell lines. These cell lines displayed different growth behaviors, i.e., continuous growth versus crisis period prior to immortalization, reflecting differential immortalization capacities of the 7 HPV-types (16/18/31/33/45/66/70) studied. In this study, cells were monitored for hypermethylation of 14 host genes (APC, CADM1, CYGB, FAM19A4, hTERT, mir124-1, mir124-2, mir124-3, MAL, PHACTR3, PRDM14, RASSF1A, ROBO3, and SFRP2) at 4 different stages during immortalization. A significant increase in overall methylation levels was seen with progression through each stage of immortalization. At stage 1 (pre-immortalization), a significant increase in methylation of hTERT, mir124-2, and PRDM14 was already apparent, which continued over time. Methylation of ROBO3 was significantly increased at stage 2 (early immortal), followed by CYGB (stage 3) and FAM19A4, MAL, PHACTR3, and SFRP2 (stage 4). Methylation patterns were mostly growth behavior independent. Yet, hTERT methylation levels were significantly increased in cells that just escaped from crisis. Bisulfite sequencing of hTERT confirmed increased methylation in immortal cells compared to controls, with the transcription core and known repressor sites remaining largely unmethylated. In conclusion, HPV-induced immortalization is associated with a sequential and progressive increase in promoter methylation of a subset of genes, which is mostly independent of the viral immortalization capacity.

Interferon treatment of human keratinocytes harboring extrachromosomal, persistent HPV-16 plasmid genomes induces de novo viral integration

Interferons (IFNs) have been used to treat epithelial lesions caused by human papillomavirus (HPV) persistence. Here, we exposed primary human keratinocytes (HFKs) immortalized by persistently replicating HPV-16 plasmid genomes to increasing levels of IFN-γ. While untreated HFKs retained replicating HPV-16 plasmids for up to 60-120 population doublings, IFN led to rapid HPV-16 plasmid loss. However, treated cultures eventually gave rise to outgrowth of clones harboring integrated HPV-16 genomes expressing viral E6 and E7 oncogenes from chimeric virus-cell mRNAs similar to those in cervical and head and neck cancers. Surprisingly, every HPV-16 integrant that arose after IFN exposure stemmed from an independent integration event into a different cellular gene locus, even within parallel cultures started from small cell inocula and cultured separately for ≥ 25 doublings to permit the rise and expansion of spontaneous integrants. While IFN treatment conferred a growth advantage upon preexisting integrants added to mixed control cultures, our results indicate that IFN exposure directly or indirectly induces HPV-16 integration, rather than only selects preexisting, spontaneous integrants that appear to be much less frequent. We estimate that IFN exposure increased integration rates by ≥ 100-fold. IFN-induced HPV-16 integration involved a wide range of chromosomal loci with less apparent selection for recurrent insertions near genes involved in cancer-related pathways. We conclude that IFNs and other potential treatments targeting high-risk HPV persistence that disrupt viral genome replication may promote increased high-risk HPV integration as a step in cancer progression. Therapies against high-risk HPV persistence thus need to be evaluated for their integration-inducing potential.

Prevalence and prognostic value of human papillomavirus genotypes in tonsillar squamous cell carcinoma: a Korean multicenter study

BACKGROUND

This study was aimed at investigating the change in the prevalence of human papillomavirus (HPV) genotypes in tonsillar squamous cell carcinoma (TSCC) and the association of the HPV genotype with the prognosis.

METHODS

This multicenter study included 175 patients with TSCC from 3 general hospitals between 1991 and 2009. HPV DNA was detected in paraffin-embedded tissues with genotyping chips. A survival analysis that considered clinicopathological factors, the HPV genotype, and the expression of p53, retinoblastoma protein, p16, and epidermal growth factor receptor (assessed with immunohistochemistry) was performed with Cox regression analysis.

RESULTS

High-risk HPV types were found in 23.4% of the cases. The prevalence of HPV-18 (10.3%) was as high as that of HPV-16 (10.3%). The proportion of high-risk HPV-positive tumors increased from 5.9% in 1991 to 31.6% in 2009. HPV-16 positivity was associated with an advanced stage and lymph node metastasis, whereas HPV-18 positivity was associated with old age and an advanced T stage. The survival analysis showed that old age and T classification were poor prognostic factors, whereas the expressions of various biomarkers were not associated with prognosis. HPV-18-positive cases had a poorer prognosis than HPV-16-positive cases and non-HPV-related TSCC cases. A multivariate analysis revealed that HPV-18 positivity, old age, and an advanced T stage were independent prognostic factors for predicting poor outcomes for patients with TSCC.

CONCLUSIONS

The proportion of HPV-positive tonsillar cancer cases has increased during the last 20 years in the Republic of Korea. The presence of HPV-18 may serve as a biomarker for a poor prognosis.

Analyzing the Human Papillomavirus (HPV) Life Cycle in Primary Keratinocytes with a Quantitative Colony-Forming Assay

Papillomavirus genomes replicate as extrachromosomal plasmids within infected keratinocytes, requiring the regulated expression of early viral gene products to initially amplify the viral genomes and subvert cell growth checkpoints as part of a complex path to immortalization. Building on contemporary keratinocyte transfection and culture systems, the methods described in this unit form a detailed approach to analyzing critical events in the human papillomavirus (HPV) life cycle, utilizing physiologic levels of viral gene products expressed from their native promoter(s) in the natural host cells for HPV infection. A quantitative colony-forming assay permits comparison of the capacities of various transfected HPV types and mutant HPV genomes to initially form colonies and immortalize human keratinocytes. In conjunction with additional methods, these protocols enable examination of genomic stability, viral and cellular gene expression, viral integration, and differentiation patterns influenced by HPV persistence in clonal human keratinocytes that effectively mimic early events in HPV infection.

Human papillomavirus (HPV)-18 E6 oncoprotein interferes with the epithelial cell polarity Par3 protein

High-risk human papillomavirus (HPV) infection is the principal risk factor for the development of cervical cancer. The HPV E6 oncoprotein has the ability to target and interfere with several PSD-95/DLG/ZO-1 (PDZ) domain-containing proteins that are involved in the control of cell polarity. This function can be significant for E6 oncogenic activity because a deficiency in cell polarisation is a marker of tumour progression. The establishment and control of polarity in epithelial cells depend on the correct asymmetrical distribution of proteins and lipids at the cell borders and on specialised cell junctions. In this report, we have investigated the effects of HPV E6 protein on the polarity machinery, with a focus on the PDZ partitioning defective 3 (Par3) protein, which is a key component of tight junctions (TJ) and the polarity network. We demonstrate that E6 is able to bind and induce the mislocalisation of Par3 protein in a PDZ-dependent manner without significant reduction in Par3 protein levels. In addition, the high-risk HPV-18 E6 protein promotes a delay in TJ formation when analysed by calcium switch assays. Taken together, the data presented in this study contribute to our understanding of the molecular mechanism by which HPVs induce the loss of cell polarity, with potential implications for the development and progression of HPV-associated tumours.

Differential in vitro immortalization capacity of eleven (probable) [corrected] high-risk human papillomavirus types

Epidemiological studies identified 12 high-risk HPV (hrHPV) types and 8 probable/possible hrHPV types that display different cancer risks. Functional studies on transforming properties of hrHPV are mainly limited to HPV16 and -18, which induce immortalization of human foreskin keratinocytes (HFKs) by successive bypass of two proliferative life span barriers, senescence and crisis. Here, we systematically compared the in vitro immortalization capacities, as well as influences on p53, pRb, hTERT, growth behavior, and differentiation capacity, of nine hrHPV types (HPV16, -18, -31, -33, -35, -45, -51, -52, and -59), and two probable hrHPV types (HPV66 and -70). By retroviral transduction, the respective E6/E7 coding sequences were expressed in HFKs from two or three independent donors. Reduced p53 levels and low-level hTERT expression in early-passage cells, as seen in HPV16-, -31-, -33-, and -35-, and to a lesser extent HPV18-transduced HFKs, was associated with continuous growth and an increased immortalization capacity. Less frequent immortalization by HPV45 and -51 and immortalization by HPV66 and -70 was preceded by an intervening period of strongly reduced growth (crisis) without prior increase in hTERT expression. Immortalization by HPV59 was also preceded by a period crisis, despite the onset of low hTERT expression at early passage. HPV52 triggered an extended life span but failed to induce immortality. Variations in p53 and pRb levels were not correlated with differences in alternative E6/E7 mRNA splicing in all hrHPV-transduced HFKs. On collagen rafts, transductants showed disturbed differentiation reminiscent of precancerous lesions. In conclusion, in vitro oncogenic capacities differ between the established hrHPV types, and both some established and probable hrHPV types display weak or moderate immortalization potential.

Sp100 provides intrinsic immunity against human papillomavirus infection

Most DNA viruses associate with, and reorganize, nuclear domain 10 (ND10) bodies upon entry into the host nucleus. In this study, we examine the roles of the ND10 components PML, Sp100, and Daxx in the establishment of human papillomavirus type 18 (HPV18) infection of primary human keratinocytes. HPV18 DNA or HPV18 quasivirus was introduced into primary human keratinocytes depleted of each ND10 protein by small interfering RNA technology, and genome establishment was determined by using a quantitative immortalization assay and measurements of viral transcription and DNA replication. Keratinocyte depletion of Sp100 resulted in a substantial increase in the number of HPV18-immortalized colonies and a corresponding increase in viral transcription and DNA replication. However, Sp100 repressed viral transcription and replication only during the initial stages of viral establishment, suggesting that Sp100 acts as a repressor of incoming HPV DNA.

IMPORTANCE

The intrinsic immune system provides a first-line defense against invading pathogens. Host cells contain nuclear bodies (ND10) that are important for antiviral defense, yet many DNA viruses localize here upon cell entry. However, viruses also disrupt, reorganize, and modify individual components of the bodies. In this study, we show that one of the ND10 components, Sp100, limits the infection of human skin cells by human papillomavirus (HPV). HPVs are important pathogens that cause many types of infection of the cutaneous and mucosal epithelium and are the causative agents of several human cancers. Understanding how host cells counteract HPV infection could provide insight into antimicrobial therapies that could limit initial infection.

Chromosome stability in tonsillar squamous cell carcinoma is associated with HPV16 integration and indicates a favorable prognosis

Tonsillar squamous cell carcinoma (TSCC) is frequently associated with human papillomavirus (HPV) and chromosome instability. Data from cellular model systems are, however, controversial concerning a relation between HPV and chromosome instability development. Here we studied this association in 77 primary TSCC with known clinical outcome and cell cycle protein expression profiles. Thirty-two tumors (42%) showed HPV16-integration. All 77 cases were analyzed by fluorescence in situ hybridization using chromosome 1- and 7-specific centromere DNA probes to detect chromosome instability, indicated by the presence of chromosome imbalances and/or polyploidization for these chromosomes. In addition, eight HPV-positive dysplasias, seven of which were adjacent to a carcinoma, were analyzed. Disomy for chromosome 1 and 7 was present in 29 out of 77 TSCC (38%), of which 19 were HPV16-positive (p = 0.002). Aneusomy was observed in the remaining 48 TSCC, of which 13 were HPV-positive. Aneusomies correlated significantly with tobacco- and alcohol consumption (p = 0.001 and p = 0.016, respectively) and a higher T-stage (p = 0.018). Both HPV-positivity and chromosome disomy were significantly associated with a favorable disease-free survival (p = 0.001 and p = 0.025, respectively). Particularly in the HPV16-positive group chromosome instability is a very strong indicator for an unfavorable prognosis (p = 0.032). In the dysplasias an identical HPV and chromosome copy number status was identified as in the adjacent tumors. We conclude that HPV-positive TSCC and their precursor lesions are more often genetically stable than HPV-negative lesions and that these tumors are associated with a favorable prognosis. Chromosome instability is an indicator for unfavorable prognosis, particularly in the HPV-positive patient group.

Differential expression of cellular microRNAs in HPV 11, -16, and -45 transfected cells

Human papillomaviruses (HPVs) are highly prevalent giving rise to both benign and malignant lesions why they are classified as high- and low-risk viruses. In this study we selected one low-risk (HPV 11) and two high-risk (HPV 16 and -45) types for genomewide miRNA analysis to investigate possible common and distinct features in the expression profiles. For this purpose we developed a cell culture model system in HaCaT cells for expression of the viral genomes under standardized conditions. We identified 25 miRNAs which were differentially regulated in two or three HPV types where 13 miRNAs were in common for all three types. Among the miRNAs identified, miR-125a-5p, miR-129-3p, miR-363, and miR-145 are related to human cancers. Noteworthy, miR-145 is found upregulated in the miRNA profiles of both high-risk HPV types. For selected differentially expressed miRNAs in HPV 16 predicted miRNA target transcript involved in signal transduction, RNA splicing and tumor invasive growth were validated by qRT-PCR. In addition, our results imply that the early 3' untranslated region (3'UTR) of the three HPV genomes were not a target for miRNA regulation.

Human papillomavirus type 16 (HPV-16) genomes integrated in head and neck cancers and in HPV-16-immortalized human keratinocyte clones express chimeric virus-cell mRNAs similar to those found in cervical cancers

Many human papillomavirus (HPV)-positive high-grade lesions and cancers of the uterine cervix harbor integrated HPV genomes expressing the E6 and E7 oncogenes from chimeric virus-cell mRNAs, but less is known about HPV integration in head and neck cancer (HNC). Here we compared viral DNA status and E6-E7 mRNA sequences in HPV-16-positive HNC tumors to those in independent human keratinocyte cell clones derived from primary tonsillar or foreskin epithelia immortalized with HPV-16 genomes. Three of nine HNC tumors and epithelial clones containing unintegrated HPV-16 genomes expressed mRNAs spliced from HPV-16 SD880 to SA3358 and terminating at the viral early gene p(A) signal. In contrast, most integrated HPV genomes in six HNCs and a set of 31 keratinocyte clones expressed HPV-16 major early promoter (MEP)-initiated mRNAs spliced from viral SD880 directly to diverse cellular sequences, with a minority spliced to SA3358 followed by a cellular DNA junction. Sequence analysis of chimeric virus-cell mRNAs from HNC tumors and keratinocyte clones identified viral integration sites in a variety of chromosomes, with some located in or near growth control genes, including the c-myc protooncogene and the gene encoding FAP-1 phosphatase. Taken together, these findings support the hypothesis that HPV integration in cancers is a stochastic process resulting in clonal selection of aggressively expanding cells with altered gene expression of integrated HPV genomes and potential perturbations of cellular genes at or near viral integration sites. Furthermore, our results demonstrate that this selection also takes place and can be studied in primary human keratinocytes in culture.

Interferon regulatory factor (IRF)-2 activates the HPV-16 E6-E7 promoter in keratinocytes

Interferon regulatory factors (IRFs) are critical mediators of gene expression, cell growth and immune responses. We previously demonstrated that interferon (IFN) induction of early viral transcription and replication in several mucosal HPVs requires IRF-1 binding to a conserved interferon response element (IRE). Here we show that the IRF-2 protein serves as a baseline transactivator of the HPV-16 major early promoter, P97. Cotransfections in IRF knockout cells confirmed that basal HPV-16 promoter activity was supported by both IRF-1 and IRF-2 complexes interacting with the promoter-proximal IRE in a dose-dependent manner. Furthermore, HPV-16 E7 expression downregulates the IRF-2 promoter, thus linking IRF-2 levels to viral transforming gene expression through a negative feedback mechanism. Taken together, these observations reveal a complex viral strategy utilizing multiple signal transduction pathways during the establishment and maintenance of HPV persistence.