Kallikreins emerge as new regulators of viral infections.

Kallikrein-related peptidases (KLKs) or kallikreins have been linked to diverse (patho) physiological processes, such as the epidermal desquamation and inflammation, seminal clot liquefaction, neurodegeneration, and cancer. Recent mounting evidence suggests that KLKs also represent important regulators of viral infections. It is well-established that certain enveloped viruses, including influenza and coronaviruses, require proteolytic processing of their hemagglutinin or spike proteins, respectively, to infect host cells. Similarly, the capsid protein of the non-enveloped papillomavirus L1 should be proteolytically cleaved for viral uncoating. Consequently, extracellular or membrane-bound proteases of the host cells are instrumental for viral infections and represent potential targets for drug development. Here, we summarize how extracellular proteolysis mediated by the kallikreins is implicated in the process of influenza (and potentially coronavirus and papillomavirus) entry into host cells. Besides direct proteolytic activation of viruses, KLK5 and 12 promote viral entry indirectly through proteolytic cascade events, like the activation of thrombolytic enzymes that also can process hemagglutinin, while additional functions of KLKs in infection cannot be excluded. In the light of recent evidence, KLKs represent potential host targets for the development of new antivirals. Humanized animal models to validate their key functions in viral infections will be valuable.

Beta-Genus Human Papillomavirus 8 E6 Destabilizes the Host Genome by Promoting p300 Degradation.

The beta genus of human papillomaviruses infects cutaneous keratinocytes. Their replication depends on actively proliferating cells and, thus, they conflict with the cellular response to the DNA damage frequently encountered by these cells. This review focus on one of these viruses (HPV8) that counters the cellular response to damaged DNA and mitotic errors by expressing a protein (HPV8 E6) that destabilizes a histone acetyltransferase, p300. The loss of p300 results in broad dysregulation of cell signaling that decreases genome stability. In addition to discussing phenotypes caused by p300 destabilization, the review contains a discussion of the extent to which E6 from other ß-HPVs destabilizes p300, and provides a discussion on dissecting HPV8 E6 biology using mutants.

APOBEC Mutagenesis Is Concordant between Tumor and Viral Genomes in HPV-Positive Head and Neck Squamous Cell Carcinoma.

APOBEC is a mutagenic source in human papillomavirus (HPV)-mediated malignancies, including HPV+ oropharyngeal squamous cell carcinoma (HPV + OPSCC), and in HPV genomes. It is unknown why APOBEC mutations predominate in HPV + OPSCC, or if the APOBEC-induced mutations observed in both human cancers and HPV genomes are directly linked. We performed sequencing of host somatic exomes, transcriptomes, and HPV16 genomes from 79 HPV + OPSCC samples, quantifying APOBEC mutational burden and activity in both host and virus. APOBEC was the dominant mutational signature in somatic exomes. In viral genomes, there was a mean of five (range 0-29) mutations per genome. The mean of APOBEC mutations in viral genomes was one (range 0-5). Viral APOBEC mutations, compared to non-APOBEC mutations, were more likely to be low-variant allele fraction mutations, suggesting that APOBEC mutagenesis actively occurrs in viral genomes during infection. HPV16 APOBEC-induced mutation patterns in OPSCC were similar to those previously observed in cervical samples. Paired host and viral analyses revealed that APOBEC-enriched tumor samples had higher viral APOBEC mutation rates (p = 0.028), and APOBEC-associated RNA editing (p = 0.008), supporting the concept that APOBEC mutagenesis in host and viral genomes is directly linked and occurrs during infection. Using paired sequencing of host somatic exomes, transcriptomes, and viral genomes, we demonstrated for the first-time definitive evidence of concordance between tumor and viral APOBEC mutagenesis. This finding provides a missing link connecting APOBEC mutagenesis in host and virus and supports a common mechanism driving APOBEC dysregulation.

mTOR Pathway Activation Assessed by Immunohistochemistry in Cervical Biopsies of HPV-associated Endocervical Adenocarcinomas (HPVA): Correlation With Silva Invasion Patterns.

The Silva pattern of invasion, recently introduced to stratify patients at risk for lymph node metastases in human papillomavirus-associated endocervical adenocarcinomas (HPVAs), can only be assessed in cone and loop electrosurgical excision procedure excisions with negative margins or in a hysterectomy specimen. Previous studies found associations between destructive stromal invasion patterns (Silva patterns B and C) and mutations in genes involved in the MEK/PI3K pathways that activate the mammalian target of rapamycin (mTOR) pathway. The primary aim of this study was to use cervical biopsies to determine whether markers of mTOR pathway activation associate with aggressive invasion patterns in matched excision specimens. The status of the markers in small biopsy specimens should allow us to predict the final and biologically relevant pattern of invasion in a resection specimen. Being able to predict the final pattern of invasion is important, since prediction as Silva A, for example, might encourage conservative clinical management. If the pattern in the resection specimen is B with lymphovascular invasion or C, further surgery can be performed 34 HPVA biopsies were evaluated for expression of pS6, pERK, and HIF1α. Immunohistochemical stains were scored semiquantitatively, ranging from 0 to 4+ with scores 2 to 4+ considered positive, and Silva pattern was determined in follow-up excisional specimens. Silva patterns recognized in excisional specimens were distributed as follows: pattern A (n=8), pattern B (n=4), and pattern C (n=22). Statistically significant associations were found comparing pS6 and pERK immunohistochemistry with Silva pattern (P=0.034 and 0.05, respectively). Of the 3 markers tested, pERK was the most powerful for distinguishing between pattern A and patterns B and C (P=0.026; odds ratio: 6.75, 95% confidence interval: 1.111-41.001). Although the negative predictive values were disappointing, the positive predictive values were encouraging: 90% for pERK, 88% for pS6 and 100% for HIF1α. mTOR pathway activation assessed by immunohistochemistry in cervical biopsies of HPVA correlate with Silva invasion patterns.

Glutathione Peroxidase (GPx) and Superoxide Dismutase (SOD) in Oropharyngeal Cancer Associated with EBV and HPV Coinfection.

Recent reports have pointed to the link between persistent inflammation, oxidative stress, and carcinogenesis; however most of the studies concerning the role of viruses in head and neck cancer (HNC) are focused mainly on one type of virus. Our present study aimed to study the relationship between Epstein-Barr virus/human papilloma virus (EBV/HPV) coinfection and glutathione peroxidase (GPx) and superoxide dismutase (SOD) level in oropharyngeal cancer. Fresh-frozen tumor tissue samples were collected from 128 patients with oropharyngeal cancer infected with EBV or HPV or with EBV/HPV coinfection. After DNA extraction, EBV and HPV DNA was detected using a polymerase chain reaction (PCR) assay. GPx and SOD activity was determined in homogenates of cancer tissue using diagnostic kits produced by Randox Laboratories. Both GPx and SOD activity was statistically lower in patients with EBV/HPV coinfection than in a single EBV or HPV infection. Analysis of GPx and SOD activity in relation to histological grading and tumor, node (TN) classification revealed that in poorly-differentiated tumors, the level of antioxidant enzymes was lower compared with well-differentiated lesions and in cases with greater tumor dimensions and lymph-node involvement, both GPx and SOD activity was decreased. Further studies are necessary to clarify the influence of interplay between EBV, HPV, and oxidative stress on malignant transformation of upper aerodigestive tract epithelial cells.

Polymorphism of MMP1 and MMP3 promoter regions and HR-HPV infection in women from Burkina Faso and Côte d'Ivoire.

The single nucleotide polymorphism (SNP) of the promoter region of MMP-1 (at 1607 bp) and MMP-3 (at 1171 bp) create Ets binding sites. Correlations between these SNPs and sensitivity to several biological processes such as metastasis and recurrence of cancer have been reported in several studies. In this case-control study, we looked for these SNPs in women infected with or not with high-risk human papillomaviruses (HR-HPV). The frequency, distribution and correlation of these SNPs with the presence or absence of HR-HPV infection were evaluated. Genotypes 1G1G, 1G2G and 2G2G for MMP1 and genotypes 5A5A, 5A6A, 6A6A for MMP3 were found in our study population. In general, we noted that the 1G (40.8%) and 2G (64.8%) alleles were more frequent in non-infected women and infected women, respectively, and more specifically this difference was significant in women from Côte d'Ivoire. These results, although yet to be reaffirmed with assays for quantifying the mRNA of these genes, suggest that the SNP of the MMP-1 promoter could promote infection with HR-HPV.

Mutations in the HPV16 genome induced by APOBEC3 are associated with viral clearance.

HPV16 causes half of cervical cancers worldwide; for unknown reasons, most infections resolve within two years. Here, we analyze the viral genomes of 5,328 HPV16-positive case-control samples to investigate mutational signatures and the role of human APOBEC3-induced mutations in viral clearance and cervical carcinogenesis. We identify four de novo mutational signatures, one of which matches the COSMIC APOBEC-associated signature 2. The viral genomes of the precancer/cancer cases are less likely to contain within-host somatic HPV16 APOBEC3-induced mutations (Fisher's exact test, P = 6.2 x 10-14), and have a 30% lower nonsynonymous APOBEC3 mutation burden compared to controls. We replicate the low prevalence of HPV16 APOBEC3-induced mutations in 1,749 additional cases. APOBEC3 mutations also historically contribute to the evolution of HPV16 lineages. We demonstrate that cervical infections with a greater burden of somatic HPV16 APOBEC3-induced mutations are more likely to be benign or subsequently clear, suggesting they may reduce persistence, and thus progression, within the host.

p53 functional states are associated with distinct aldehyde dehydrogenase transcriptomic signatures.

p53 and aldehyde dehydrogenase (ALDH) have been implicated in key tumorigenesis processes including cancer initiating cell (CIC) maintenance; however, the relationship between these two mediators remains poorly defined. In this study, ALDH isoform expression diversity was revealed in CICs with disparate p53 functional states: gain of function, high risk p53 mutation (p53HRmut) and wildtype p53 (p53WT) inactivated by the human papillomavirus 16 (HPV16) E6 oncogene. Interrogation of head and neck squamous cell carcinoma (HNSCC) cell lines and patient tumors showed that HPV16+/p53WT cases have higher ALDH variance score (AVS), a measure of tumor ALDH isoform expression diversity, compared to HPV-/p53HRmut cases (p = 0.03). AVS and several individual ALDH isoforms were associated with prognosis in HPV16+/p53WT HNSCC but not in HPV-/p53HRmut HNSCC. Knockdown of the dominant ALDH isoform in high AVS HNSCC depleted the CIC pool in vitro and in vivo. Our results demonstrate that p53 functional states are associated with distinct ALDH isoform transcriptomic signatures. Moreover, tumor ALDH profiling may provide insight on which ALDH isoform to target in high AVS HNSCC tumors to deplete the CIC population.

Multiple regions of E6AP (UBE3A) contribute to interaction with papillomavirus E6 proteins and the activation of ubiquitin ligase activity.

The HECT domain E3 ubiquitin ligase E6AP (UBE3A) is critical for the development of human papillomavirus (HPV) associated cancers, the neurodevelopment disorder Angelman Syndrome, and some cases of autism spectrum disorders. How E6AP recognizes its cellular targets and how its ubiquitin ligase activity is triggered remain poorly understood, and HPV E6 proteins are models for these processes. We examined diverse E6 proteins from human and non-human papillomaviruses and identified two different modes of interaction between E6 and E6AP. In Type I interactions, E6 can interact directly with the LXXLL peptide motif alone of E6AP (isolated from the rest of E6AP), and then recruit cellular substrates such as p53. In Type II interactions, E6 proteins require additional auxiliary regions of E6AP in either the amino terminus or in the carboxy-terminal HECT domain to interact with the LXXLL peptide motif of E6AP. A region of E6AP amino-terminal to the LXXLL peptide motif both augments association with E6 proteins and is required for E6 proteins to trigger ubiquitin ligase activity in the carboxy-terminal HECT ubiquitin ligase domain of E6AP. In Type I interactions, E6 can associate with E6AP and recruit p53, but a Type II interaction is required for the degradation of p53 or NHERF1. Interestingly, different E6 proteins varied in E6AP auxiliary regions that contributed to enhanced association, indicating evolutionary drift in the formation of Type II interactions. This classification of E6-E6AP interaction types and identification of a region in the E6AP amino terminus that is important for both E6 association and stimulation of ubiquitin ligase activity will inform future structural data of the E6-E6AP complex and future studies aiming to interfere with the activity of the E6-E6AP complex.

Genomic alterations in STK11 can predict clinical outcomes in cervical cancer patients.

OBJECTIVE: Cervical cancer is the fourth most common cause of cancer-related deaths in Asian women, due to its poor prognosis. This study aimed to decipher genomic alteration profiles of a cohort of Japanese cervical cancer patients to understand why certain patients benefited from molecular targeted therapies and their prognostic significance. METHODS: During 2008-2018, 154 cervical cancer patients underwent a potentially curative resection procedure at the National Cancer Center Hospital. Genomic DNA samples were analyzed using Ion AmpliSeq™ Cancer Hotspot Panel v2. Alterations in the copy number of PIK3CA, ERBB2, PTEN, and STK11 were detected using the TaqMan assay. HPV-positive results were confirmed by genomic testing and in situ hybridization assay. RESULTS: The frequency of genomic alterations in PIK3CA (36%), STK11 (16%), PTEN (11%), TP53 (11%), and KRAS (8%) was >5%. KRAS mutations were preferentially detected in patients with adenocarcinomas, and the frequency of PIK3CA mutations in patients with squamous cell carcinomas was higher than that in patients with other histological cancer types. HPV-positive results were observed in 139/154 (90.3%) patients, and TP53 mutants were detected in HPV-negative specimens. In this study, the overall survival of patients with genomic alterations in STK11 was worse than in patients with wild-type STK11 (hazard ratio = 10.6, P = 0.0079) and TCGA dataset (hazard ratio = 2.46, P = 0.029). CONCLUSIONS: More than one-third of Japanese cervical cancer patients exhibit mutations targeted by molecular targeted therapies. We have proposed the prognostic value of STK11 genomic alterations.

Induction of co-inhibitory molecule CTLA-4 by human papillomavirus E7 protein through downregulation of histone methyltransferase JHDM1B expression.

Human papillomavirus causes various skin diseases and even cancer. Unfortunately, the host immune system often fails to generate effective responses against HPV infection due to the ability of HPV to evade immune-mediated eradication, although the detailed mechanisms by which HPV inhibits host antiviral immunity are not fully understood. In this study, we reported a novel role of HPV E7 oncoprotein in inducing the expression of co-inhibitory molecule cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) in cells of epithelial origin. Mechanistically, HPV E7 protein downregulated the cellular abundance of Jumonji C histone demethylase 1B (JHDM1B), increasing the levels of H3K36 methylation within the promoter region of CTLA-4. Our findings expand the current understanding of HPV-mediated immune evasion mechanisms and may be helpful in developing optimal anti-HPV therapeutic strategies and relevant drugs.

HPV-16 Infection Is Associated with a High Content of CD39 and CD73 Ectonucleotidases in Cervical Samples from Patients with CIN-1.

The development of cervical cancer (CeCa) is associated with high-risk human papilloma virus (HR-HPV) infections, mainly HPV-16, which is present in more than 50% of cases. The presence of immunosuppressive factors in the early stages of the disease is also strongly linked to CeCa progression. In this context, it is unknown whether ectonucleotidases CD39 and CD73, which are involved in the production of adenosine (Ado) that suppresses the specific antitumor immune response, are present in precursor lesions of CeCa. In this pilot study, we analyzed the presence of CD39 and CD73 and their capacity to generate Ado in 25 cervical samples from patients with grade 1 cervical intraepithelial neoplasms (CIN-1) and 25 samples from normal donors (NDs) free of HPV infection. Cells obtained from cervical samples of CIN-1 patients positive for HPV-16 showed higher CD39 and CD73 contents compared to samples obtained from CIN-1 patients negative for HPV-16 and NDs. Interestingly, solubilized cervical mucus from these patients also showed higher contents of soluble CD39 and CD73, which were associated with a greater capacity to produce Ado from the hydrolysis of adenosine triphosphate (ATP) and adenosine monophosphate (AMP). In addition, serum samples of these patients showed higher levels of TGF-ß than those of CIN-1 patients negative for HPV-16 and ND. These results suggest that persistent infection with HR-HPV, mostly HPV-16, in CIN-1 patients may promote the expression of CD39 and CD73 through the production of TGF-ß in precursor lesions to generate an immunosuppressive microenvironment and allow its progression to CeCa.

Association of the MUTYH Gln324His (CAG/CAC) variant with cervical carcinoma and HR-HPV infection in a Chinese population.

This study was performed to investigate the relationship between the MUTYH Gln324His (CAG/CAC) genotype and risk of cervical squamous cell carcinoma (CSCC) in a case-control setting. Mismatch amplification-polymerase chain reaction (MA-PCR) was applied to detect the polymorphism in 400 CSCC, 400 CIN III and 1200 control participants. The homozygous His324His (CAC/CAC) genotype of MUTYH was associated with significantly increased risk of CIN III (OR = 1.94) and CSCC (OR = 3.83). Increased risk of CIN III (OR = 1.34) and CSCC (OR = 1.97) was additionally observed with the heterozygous CAG/CAC genotype. Overall, individuals in both CAC/CAC and CAG/CAC genotype groups were at higher risk of cervical carcinoma (CINIII (OR = 1.46) and CSCC (OR = 2.34)). Within the HR-HPV infection-positive group, CAC/CAC and CAG/CAC genotypes were significantly enriched in relation to CIN III and CSCC. Moreover, we observed a positive correlation between the proportion of homozygous CAC/CAC MUTYH genotype and malignant prognostic factors of CSCC, such as cell differentiation grade and lymph node metastasis. These findings clearly highlight associations between the MUTYH Gln324His (CAG/CAC) polymorphism and susceptibility to CSCC, HR-HPV infection and specific prognostic factors, supporting the utility of this variant as an early indicator for patients at high risk of cervical carcinoma.

The Deubiquitinase USP46 Is Essential for Proliferation and Tumor Growth of HPV-Transformed Cancers.

High-risk human papilloma viruses (HPVs) cause cervical, anal, and oropharyngeal cancers, unlike the low-risk HPVs, which cause benign lesions. E6 oncoproteins from the high-risk strains are essential for cell proliferation and transformation in HPV-induced cancers. We report that a cellular deubiquitinase, USP46, is selectively recruited by the E6 of high-risk, but not low-risk, HPV to deubiqutinate and stabilize Cdt2/DTL. Stabilization of Cdt2, a component of the CRL4Cdt2 E3 ubiquitin ligase, limits the level of Set8, an epigenetic writer, and promotes cell proliferation. USP46 is essential for the proliferation of HPV-transformed cells, but not of cells without HPV. Cdt2 is elevated in human cervical cancers and knockdown of USP46 inhibits HPV-transformed tumor growth in xenografts. Recruitment of a cellular deubiquitinase to stabilize key cellular proteins is an important activity of oncogenic E6, and the importance of E6-USP46-Cdt2-Set8 pathway in HPV-induced cancers makes USP46 a target for the therapy of such cancers.

USP15 inhibits HPV16 E6 degradation and catalytically inactive USP15 has reduced inhibitory activity.

High-risk human papillomaviruses (HPVs) possess transforming activity leading to development of the cancer, including oropharyngeal, anal, penile, vulvar, vaginal, and cervical cancer. The stability of E6 is essential for its complete function as an oncoprotein. Using the yeast two-hybrid system, we identified ubiquitin-specific protease 15 (USP15) as an HPV16 E6-interacting protein. USP15 cleaves polyubiquitin chains of HPV16 E6 and/or ubiquitin precursors. Our results indicate that USP15 could increase the level of HPV16 E6 by inhibiting E6 degradation. USP15 inhibited the degradation of HPV16 E6 in dose-dependent manner. In contrast, catalytically inactive mutants of USP15 had a reduced inhibitory effect on E6 degradation. In particular, USP15 mutants of all three cysteine boxes and the NHL mutant of the KRF box had a drastically reduced inhibitory effect on HPV16 E6 degradation. In addition, HPV16 E6 mRNA was not induced by USP15; therefore, HPV16 E6 appears to be post-translationally regulated. These results suggest that USP15 has the ability to stabilize E6 as a deubiquitinating enzyme, and as an oncoprotein affects biological functions in infected human cells.

Downregulation of the α1- and ß1-subunit of sGC in Arterial Smooth Muscle Cells of OPSCC Is HPV-Independent.

The nitric oxide (NO)-sensitive soluble guanylyl cyclase (sGC) is a heterodimeric enzyme with an α and ß subunit. NO binds to heme of the ß1-subunit of sGC, activates the enzyme in the reduced heme iron state in vascular smooth muscle cells (VSMCs), and generates cGMP-inducing vasodilatation and suppression of VSMC proliferation. In the complex tumor milieu with higher levels of reactive oxygen species (ROS), sGC heme iron may become oxidized and insensitive to NO. To change sGC from an NO-insensitive to NO-sensitive state or NO-independent manner, protein expression of sGC in VSMC is required. Whether sGCα1ß1 exists at the protein level in arterial VSMCs of oropharyngeal squamous cell carcinoma (OPSCC) is unknown. In addition, whether differences in the genetic profile between human papillomavirus (HPV)-positive and HPV-negative OPSCC contributes to the regulation of sGCα1ß1 is unclear. Therefore, we compared the effects of HPV-positive and HPV-negative OPSCC on the expression of sGCα1ß1 in arterial VSMCs from tumor-free and tumor-containing regions of human tissue sections using quantitative immunohistochemistry. In comparison to the tumor-free region, we found a decrease in expression of both α1- and ß1-subunits in the arterial VSMC layer of the tumor-containing areas. The OPSCC-induced significant downregulation of the α1- and ß1-subunits of sGC in arterial VSMC was HPV-independent. We conclude that the response of sGC to NO in tumor arterial VSMCs may be impaired by oxidation of the heme of the ß1-subunit, and thus, α1- and ß1-subunits of sGC could be targeted to degradation under oxidative stress in OPSCC in an HPV-independent manner. The degradation of sGCα1ß1 in VSMCs may result in increased proliferation of VSMCs, promoting tumor arteriogenesis in OPSCC. This can be interrupted by preserving the active heterodimer sGCα1ß1 in arterial VSMCs.

Acid sphingomyelinase activity as an indicator of the cell stress in HPV-positive and HPV-negative head and neck squamous cell carcinoma.

Human papillomavirus (HPV) infection, especially HPV-16 and HPV-18, has been increasingly associated with head and neck squamous cell carcinoma. The treatment of HPV-positive squamous cell carcinoma has a better response to both radiotherapy and chemotherapy and presents a better prognosis for the patient. Defining the underlying mechanism of the difference might help in developing future treatment options and could be an important factor in personal therapy planning. Endogenously secreted acid sphingomyelinase (ASMase) levels in the cellular stress caused by irradiation and cisplatin were investigated. MTT assay was performed to evaluate the viability of the treated cells. Keratinocytes were used to evaluate the effects of radiation on normal tissues. Irradiation caused a dose-dependent increase in ASMase activity in both SCC9 HPV-negative, and UDSCC2 HPV-positive cells. ASMase activity in UDSCC2 cells was significantly higher than that in SCC9 cells. UDSCC cells were more sensitive to cisplatin treatment than SCC cells, and the dose-response in the activity was observed in long-time treatments when high doses of cisplatin were used. The results of the current study have clearly showed that HPV positivity should be considered as one of the determinative factors which should be considered when tumor treatments are planned. However, further studies are needed to determine the differences in cellular responses and pathways among HPV-negative and HPV-positive cells.

SIRT1 overexpression in cervical squamous intraepithelial lesions and invasive squamous cell carcinoma.

Invasive squamous cell carcinoma (SCC) of the cervix involves the progression of premalignant cervical intraepithelial neoplasia (CIN) and is associated with persistent human papillomavirus infection. Most CINs will regress, and the challenge is to identify the lesions likely to progress to invasive cancer. We evaluated Sirtuin 1 (SIRT1) expression in nonneoplastic cervix, CINs, and SCCs as a potential biomarker to predict disease progression. A total of 101 cases were selected including 29 CIN 1s, 32 CIN 2s, 16 CIN 3s, 2 microinvasive SCCs, and 22 invasive SCCs. Cervical nonneoplastic squamous epithelium showed weak positivity of SIRT1 in the basal layer. SIRT1 cytoplasmic overexpression was found in 13.8% of CIN 1s (4/29), 40.6% of CIN 2s (13/32), and 50% of CIN 3s (8/16), and it was statistically significant between CIN 1 and CIN 2/3 lesions (P=.01). All 24 cases of invasive and microinvasive SCC showed SIRT1 overexpression, with 25% (6/24) showing cytoplasmic staining only, 4.2% (1/24) showing nuclear staining only, and 70.8% (17/24) showing both nuclear and cytoplasmic staining. From CIN 1 to SCC, SIRT1 expression showed steady and statistically significant increase (CIN 1 versus CIN 2-3, P=.01; CIN 2-3 versus SCC, P=.0001). Thus, SIRT1 may serve as a potential biomarker for predicting the progression of CIN to invasive SCC.

Activation of telomerase by HPVs.

Telomerase extends the ends of linear chromosomes, and its expression leads to cellular immortalization. In HPV-associated cancers, telomerase is universally detected, and this occurs by activation of the catalytic subunit of telomerase, hTERT. The expression of hTERT is affected by both high-risk HPV E6 and E7. Seminal studies over the last two decades have identified the transcriptional, epigenetic, and post-transcriptional roles high-risk E6 and E7 have in telomerase regulation. This review will summarize these findings and highlight the importance of telomerase activation as an oncogenic pathway in HPV-associated cancer development and progression.