Differential roles of p16INK4A and p14ARF genes in prognosis of oral carcinoma

Role of DNA Methylation Profiles as Potential Biomarkers and Novel Therapeutic Targets in Head and Neck Cancer

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide and is associated with high mortality. The main reasons for treatment failure are a low rate of early diagnosis, high relapse rates, and distant metastasis with poor outcomes. These are largely due to a lack of diagnostic, prognostic, and predictive biomarkers in HNSCC. DNA methylation has been demonstrated to play an important role in the pathogenesis of HNSCC, and recent studies have also valued DNA methylation as a potential biomarker in HNSCC. This review summarizes the current knowledge on DNA methylation profiles in HPV-positive and HPV-negative HNSCC and how these may contribute to the pathogenesis of HNSCC. It also summarizes the potential value of DNA methylation as a biomarker in the diagnosis, prognosis, and prediction of the response to therapy. With the recent immunotherapy era in head and neck treatment, new strategies to improve immune responses by modulating TIMEs have been intensely investigated in early-phase trials. Therefore, this study additionally summarizes the role of DNA methylation in the regulation of TIMEs and potential predictive immunotherapy response biomarkers. Finally, this study reviews ongoing clinical trials using DNA methylation inhibitors in HNSCC.

A novel EZH2/NXPH4/CDKN2A axis is involved in regulating the proliferation and migration of non-small cell lung cancer cells

NXPH4 is discovered to be a neuropeptide-like glycoprotein, belonging to the Neurexophilins (Nxphs) family. NXPH4 shares a similar domain structure with NXPH1, which, however, is poorly understood in terms of its function. Bioinformatics analysis and experimental verification in this study confirmed the abnormal high expression of NXPH4 in non-small cell lung cancer (NSCLC) tissues and cells. Knockdown of NXPH4 by siRNA can inhibit the proliferation and migration of cells, resulting in significant cell cycle arrest in S1 phase. Furthermore, in NSCLC cells, NXPH4 was regulated by transcriptional activation of enhancer of zeste homolog 2 (EZH2) in its upstream. While downstream, NXPH4 could interact with CDKN2A and downregulate its protein stability, thus participating in the cell cycle regulation through interacting with cyclinD-CDK4/6-pRB-E2F signaling pathway. To sum up, the present study reveals a regulatory pathway of EZH2/NXPH4/CDKN2A in NSCLC, providing possible reference for understanding the function of NXPH4 in tumors.

Alcohol and Head and Neck Cancer: Updates on the Role of Oxidative Stress, Genetic, Epigenetics, Oral Microbiota, Antioxidants, and Alkylating Agents

Head and neck cancer (HNC) concerns more than 890,000 patients worldwide annually and is associated with the advanced stage at presentation and heavy outcomes. Alcohol drinking, together with tobacco smoking, and human papillomavirus infection are the main recognized risk factors. The tumorigenesis of HNC represents an intricate sequential process that implicates a gradual acquisition of genetic and epigenetics alterations targeting crucial pathways regulating cell growth, motility, and stromal interactions. Tumor microenvironment and growth factors also play a major role in HNC. Alcohol toxicity is caused both directly by ethanol and indirectly by its metabolic products, with the involvement of the oral microbiota and oxidative stress; alcohol might enhance the exposure of epithelial cells to carcinogens, causing epigenetic modifications, DNA damage, and inaccurate DNA repair with the formation of DNA adducts. Long-term markers of alcohol consumption, especially those detected in the hair, may provide crucial information on the real alcohol drinking of HNC patients. Strategies for prevention could include food supplements as polyphenols, and alkylating drugs as therapy that play a key role in HNC management. Indeed, polyphenols throughout their antioxidant and anti-inflammatory actions may counteract or limit the toxic effect of alcohol whereas alkylating agents inhibiting cancer cells' growth could reduce the carcinogenic damage induced by alcohol. Despite the established association between alcohol and HNC, a concerning pattern of alcohol consumption in survivors of HNC has been shown. It is of primary importance to increase the awareness of cancer risks associated with alcohol consumption, both in oncologic patients and the general population, to provide advice for reducing HNC prevalence and complications.

Genetic and methylation status of CDKN2A (p14ARF/p16INK4A) and TP53 genes in recurrent respiratory papillomatosis

Recurrent respiratory papillomatosis (RRP) is a rare and chronic disease affecting the upper airway with papillomatous lesions caused by the human papillomavirus (HPV) infection, especially HPV-6 and/or HPV-11 types. Little is known about the genetic and epigenetic drivers in RRP pathophysiology. For this purpose, we analyzed 27 papillomatous lesions from patients with RRP to evaluate somatic mutations and methylation status in CDKN2A (p14^ARF/p16^INK4A) and TP53, which are key tumor suppressor genes for the cell cycle control. Sanger sequencing analysis revealed one somatic mutation in TP53 (c.733_734insA) and four mutations in CDKN2A (c.-30G > T, c.29_30insA, c.69delT, and c.300C > A). These mutations were observed in 10 patients, 6 of which carried double mutation. Furthermore, 50% (5/10) of these patients carrying somatic mutations had RRP severity, representing 62.5% (5/8) of the severity cases in this study, albeit no significant association was found between somatic mutations and disease severity. Methylation-specific polymerase chain reaction assays revealed p14^ARF promoter hypermethylation in 100% of cases, followed by TP53 (96.3%) and p16^INK4A (55.6%), suggesting the influence of HPV in the DNA methylation machinery. In conclusion, somatic mutations were not common events identified in patients with RRP. However, epigenetic modulation by high methylation rates, particularly for the p14^ARF/TP53 pathway, seems to be in the course of RRP development.

DNA methylation in oral squamous cell carcinoma: from its role in carcinogenesis to potential inhibitor drugs

DNA methylation is one of epigenetic changes most frequently studied nowadays, together with its relationship with oral carcinogenesis. A group of enzymes is responsible for methylation process, known as DNA methyltransferases (DNMT). Although essential during embryogenesis, DNA methylation pattern alterations, including global hypomethylation or gene promoter hypermethylation, can be respectively associated with chromosomal instability and tumor suppressor gene silencing. Higher expression of DNA methyltransferases is a common finding in oral cancer and may contribute to inactivation of important tumor suppressor genes, influencing development, progression, metastasis, and prognosis of the tumor. To control these alterations, inhibitor drugs have been developed as a way to regulate DNMT overexpression, and they are intended to be associated with ongoing chemo- and radiotherapy in oral cancer treatments. In this article, we aimed to highlight the current knowledge about DNA methylation in oral cancer, including main hyper/hypomethylated genes, DNMT expression and its inhibitor treatments.

Post-Translational Regulation of ARF: Perspective in Cancer

Tumorigenesis can be induced by various stresses that cause aberrant DNA mutations and unhindered cell proliferation. Under such conditions, normal cells autonomously induce defense mechanisms, thereby stimulating tumor suppressor activation. ARF, encoded by the CDKN2a locus, is one of the most frequently mutated or deleted tumor suppressors in human cancer. The safeguard roles of ARF in tumorigenesis are mainly mediated via the MDM2-p53 axis, which plays a prominent role in tumor suppression. Under normal conditions, low p53 expression is stringently regulated by its target gene, MDM2 E3 ligase, which induces p53 degradation in a ubiquitin-proteasome-dependent manner. Oncogenic signals induced by MYC, RAS, and E2Fs trap MDM2 in the inhibited state by inducing ARF expression as a safeguard measure, thereby activating the tumor-suppressive function of p53. In addition to the MDM2-p53 axis, ARF can also interact with diverse proteins and regulate various cellular functions, such as cellular senescence, apoptosis, and anoikis, in a p53-independent manner. As the evidence indicating ARF as a key tumor suppressor has been accumulated, there is growing evidence that ARF is sophisticatedly fine-tuned by the diverse factors through transcriptional and post-translational regulatory mechanisms. In this review, we mainly focused on how cancer cells employ transcriptional and post-translational regulatory mechanisms to manipulate ARF activities to circumvent the tumor-suppressive function of ARF. We further discussed the clinical implications of ARF in human cancer.

Specific Deletion of p16INK4a with Retention of p19ARF Enhances the Development of Invasive Oral Squamous Cell Carcinoma

The cyclin-dependent kinase inhibitor 2A (CDKN2A)/alternate reading frame (ARF) locus consists of two overlapping tumor suppressor genes, p16^INK4a and p14^ARF (p19^ARF in mice), encoding two unrelated proteins in alternative reading frames. Previous reports suggest that p16^INK4a and p14^ARF alterations independently exhibit differential roles, and p16^INK4a is more closely associated with a poor prognosis in oral cancer. However, the role of p16^INK4a-specific loss in oral squamous cell carcinogenesis remains unclear. The authors assessed chemical carcinogen 4-nitroquinoline 1-oxide (4NQO)-induced multistep oral squamous cell carcinogenesis in mice carrying p16^INK4a-specific loss with retention of the p19^ARF gene (p16^INK4a-/-). 4NQO-treated p16^-/- mice exhibited a higher incidence and multiplicity of oral squamous cell carcinoma (OSCC) development relative to 4NQO-treated wild-type mice. 4NQO-treated p16^INK4a-/- OSCC cells exhibited higher proliferation and up-regulation of Arf, transcription factor E2f1, tumor protein p63 (tp63), and oncogenic ΔNp63, an isoform p63, compared with observations in 4NQO-treated wild-type OSCC cells. Furthermore, the overexpression of oncogenic ΔNp63 was associated with human OSCC. In conclusion, these results in mice indicate the biological significance of p16^INK4a-specific loss with retention of p19^ARF in oral squamous cell carcinogenesis, and ΔNp63 may be a potential target for OSCC.

Promoter DNA Methylation and mRNA Expression Level of p16 Gene in Oral Squamous Cell Carcinoma: Correlation with Clinicopathological Characteristics

The aim of this study was to investigate the relationship between p16 methylation and its expression in oral squamous cell carcinoma (OSCC). Also the contribution of clinicopathological factors, HPV infection and smoking in p16 expression and promoter methylation has been investigated. In this study 67 consecutive OSCC patients and 59 normal individuals were enrolled. All patients were candidates for surgery of oral cavity and fresh tumor biopsies were collected and processed for DNA and RNA extraction. Normal gingival tissues were collected from individuals referred to dentistry clinic and considered as controls. All the cases and controls were checked for HPV infection and then promoter methylation and expression of p16 gene were determined using Methylation-specific PCR (MSP) and real-time PCR (QPCR), respectively. Methylation of p16 in tumors and normal tissues were 59.7 and 38.9%, respectively. Most of hypermethylated samples (>82%) were in high grades. P16 methylation was comparable in HPV+ and HPV- patients or smokers. P16 was overexpressed (~3 fold; p = 0.044) in HPV+ tumors, but it was significantly down-regulated in smoker patients (40% of all tumors). Comparison of P16 expression in OSCC tumors with different degrees of promoter methylation further suggest the relationship of methylation rate and down-regulation of P16 expression. The p16 methylation and expression was differentially affected in patients with HPV infection and the smoker cases. Regardless of the influence of environmental factors, it appears that P16 status is useful for classifying patients with OSCC and for influencing treatment strategies in accordance with this classification. Moreover, targeting the upregulation of p16 could be a promising therapeutic option.

Regulatory Network of ARF in Cancer Development

ARF is a tumor suppressor protein that has a pivotal role in the prevention of cancer development through regulating cell proliferation, senescence, and apoptosis. As a factor that induces senescence, the role of ARF as a tumor suppressor is closely linked to the p53-MDM2 axis, which is a key process that restrains tumor formation. Thus, many cancer cells either lack a functional ARF or p53, which enables them to evade cell oncogenic stress-mediated cycle arrest, senescence, or apoptosis. In particular, the ARF gene is a frequent target of genetic and epigenetic alterations including promoter hyper-methylation or gene deletion. However, as many cancer cells still express ARF, pathways that negatively modulate transcriptional or post-translational regulation of ARF could be potentially important means for cancer cells to induce cellular proliferation. These recent findings of regulators affecting ARF protein stability along with its low levels in numerous human cancers indicate the significance of an ARF post-translational mechanism in cancers. Novel findings of regulators stimulating or suppressing ARF function would provide new therapeutic targets to manage cancer- and senescence-related diseases. In this review, we present the current knowledge on the regulation and alterations of ARF expression in human cancers, and indicate the importance of regulators of ARF as a prognostic marker and in potential therapeutic strategies.

Analysis of Methylation Patterns and Expression Profiles of P14Arf Gene in Patients with Oral Squamous Cell Carcinoma

Aims

To analyze the promoter methylation profile and mRNA expression of the p14ARF gene in oral squamous cell carcinoma (OSCC).

Methods

Promoter methylation of the p14ARF gene was investigated by methylation-specific polymerase chain reaction in paraffin-embedded tissues from 76 patients with OSCC and 57 oral tissues used as healthy controls. Expression of p14ARF mRNA was also determined using real-time quantitative reverse-transcription PCR. The methylation status and mRNA level profile of the gene and their relationship with clinical data were analyzed.

Results

Methylation of the p14ARF gene in OSCC was significantly increased compared to normal control tissues (χ2 = 16.73, p<0.0001). The relative expression of p14ARF mRNA in OSCC was not significantly different from that in healthy control samples.

Conclusion

Promoter methylation of p14ARF may be an important mechanism in OSCC, and its determination may be considered an important tool in the early diagnosis and treatment of OSCC.

Current Insights into Oral Cancer Epigenetics

Epigenetic modifications have emerged into one of the cancer hallmarks, replacing the concept of malignant pathologies as being solely genetic-based conditions. The epigenetic landscape is responsible for normal development but also for the heterogeneity among tissues in terms of gene expression patterns. Dysregulation in these mechanisms has been associated with disease stage, and increased attention is now granted to cancer in order to take advantage of these modifications in terms of novel therapeutic strategies or diagnosis/prognosis tools. Oral cancer has also been subjected to epigenetic analysis with numerous studies revealing that the development and progression of this malignancy are partially induced by an altered epigenetic substrate together with genetic alterations and prolonged exposure to environmental risk factors. The present review summarizes the most important epigenetic modifications associated with oral cancer and also their potential to be used as new therapeutic targets.

In vitro and in silico validation of CA3 and FHL1 downregulation in oral cancer

Background

Aberrant methylation is a frequent event in oral cancer.

Methods

In order to better characterize these alterations, a search for genes downregulated by aberrant methylation in oral squamous cell carcinoma (OSCC) was conducted through the mining of ORESTES dataset. Findings were further validated in OSCC cell lines and patients’ samples and confirmed using TCGA data. Differentially expressed genes were identified in ORESTES libraries and validated in vitro using RT-PCR in HNSCC cell-lines and OSCC tumor samples. Further confirmation of these results was performed using mRNA expression and methylation data from The Cancer Genome Atlas (TCGA) data.

Results

From the set of genes selected for validation, CA3 and FHL1 were downregulated in 60% (12/20) and 75% (15/20) of OSCC samples, respectively, and in HNSCC cell lines. The treatment of cell lines JHU-13 and FaDu with the demethylating agent 5'-aza-dC was efficient in restoring CA3 and FHL1 expression. TCGA expression and methylation data on OSCC confirms the downregulation of these genes in OSCC samples and also suggests that expression of CA3 and FHL1 is probably regulated by methylation. The downregulation of CA3 and FHL1 observed in silico was validated in HNSCC cell lines and OSCC samples, showing the feasibility of integrating different datasets to select differentially expressed genes in silico.

Conclusions

These results showed that the downregulation of CA3 and FHL1 data observed in the ORESTES libraries was validated in HNSCC cell lines and OSCC samples and in a large cohort of samples from the TCGA database. Moreover, it suggests that expression of CA3 and FHL1 could probably be regulated by methylation having an important role the oral carcinogenesis.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4077-3) contains supplementary material, which is available to authorized users.

Genetic and epigenetic alterations in the tumour, tumour margins, and normal buccal mucosa of patients with oral cancer

Despite adequate surgical resection, oral squamous cell carcinoma (OSCC) shows a high rate of recurrence and metastasis, which could be explained by the presence of molecular alterations in seemingly normal tumour margins and the entire oral mucosa. The aims of this study were (1) to assess the presence of gene amplification (c-Myc and HER2) and promoter methylation (p14 and p16) in the tumours, tumour margins, and unaffected oral mucosa of 40 OSCC patients, and (2) to evaluate the possibility of using these alterations as prognostic markers. c-Myc and HER2 genes were quantified by means of real-time PCR (qPCR), and p14 and p16 methylation status was determined by methylation-specific PCR (MSP PCR). All tissues examined exhibited molecular alterations in various proportions. Tumour tissues, as expected, showed the highest prevalence of alterations, while oral mucosa showed the lowest. Multiple alterations (co-alterations) in tumours and tumour margins were significantly more frequent than in unaffected oral mucosa (P<0.001 and P=0.027, respectively). HER2 amplification in margin tissue (P<0.001) and swabs (P=0.013), as well as the existence of three co-alterations in margins (P=0.001) and macroscopically unaffected oral mucosa (P<0.001) were correlated with shorter disease-specific survival.

An immunohistochemical score to predict the outcome for oral squamous cell carcinoma

BACKGROUND

Oral cancer is a major public health problem worldwide, with a poor survival. Our aim was to evaluate several protein markers in oral squamous cell carcinomas (OSCC) and analyse their prognostic value on patient's survival.

METHODS

We analysed the expression of EGFR, p53, p27, p16, cyclin D1, cyclin A2, COX-2, Ki-67, Bcl-2, VEGFR-1 and VEGFR-2, by immunohistochemistry on 67 primary OSCC. Cancer-specific survival (CSS) analysis was evaluated by the Cox regression model.

RESULTS

Markers showed variable expression between 27.9% and 95.2%. In univariate analysis for CSS, we found that four of the tested markers, namely high expression of p53 (P = .001), EGFR (P = .003), cyclin A2 (P = .005) and low expression of p16 (P = .019), along with clinical stage (P < .001), tumour size (P < .001), presence of nodal metastasis (P < .001) and perineural permeation (P = .039) were related to decreased survival. On the basis of these results, we constructed an immunohistochemical score hinging on the possibility that any tumour could express none of these four markers (score 0), one or two markers (score 1) and three or more markers (score 2). In multivariable analysis, this immunohistochemical score revealed an independent prognostic value on cancer-specific survival (P = .001; HR: 3.7: 95%CI 1.7-7.9). Moreover, we confirmed that in early-stage tumours (stage I or II) this score maintained its independent prognostic value (P = .025; HR: 7.9, 95%CI 1.3-49.1) on CSS.

CONCLUSION

The expression of the markers p53, p16, EGFR and cyclin A in OSCC, combined to give an immunohistochemical score, may identify high-risk subgroups for decreased survival and to further guide therapeutic decisions.

Dynamics of ARF regulation that control senescence and cancer

ARF is an alternative reading frame product of the INK4a/ARF locus, inactivated in numerous human cancers. ARF is a key regulator of cellular senescence, an irreversible cell growth arrest that suppresses tumor cell growth. It functions by sequestering MDM2 (a p53 E3 ligase) in the nucleolus, thus activating p53. Besides MDM2, ARF has numerous other interacting partners that induce either cellular senescence or apoptosis in a p53-independent manner. This further complicates the dynamics of the ARF network. Expression of ARF is frequently disrupted in human cancers, mainly due to epigenetic and transcriptional regulation. Vigorous studies on various transcription factors that either positively or negatively regulate ARF transcription have been carried out. However, recent focus on posttranslational modifications, particularly ubiquitination, indicates wider dynamic controls of ARF than previously known. In this review, we discuss the role and dynamic regulation of ARF in senescence and cancer.

The Loss of p16 Expression Worsens the Prognosis of OSCC

Oral squamous cell carcinoma is the most common neoplasia of the mouth. Downregulation of p16(INK4a) (a cyclin-dependent kinase inhibitor) has been reported for mouth cancer and it is believed that its inactivation is an early event in oral carcinogenesis. The goal of this article is to quantitatively report expression of p16(INK4a) and the state of methylation in oral squamous cell carcinoma, and evaluate its relationship with the clinical and prognostic factors, in addition to setting out a multivariate model that predicts survival. The mean expression of p16(INK4a) was 7.70 (SD=14.07) (F=0.894; P=0.449). According to the semiquantitative analysis, there were statistically significant differences, where 19 cases were negative (<2 %), 11 at initial stages, and 8 at advanced stages (χ(2)=6.016; P<0.05). The methylation of p16(INK4a) was not associated with any of the clinical or pathologic variables. Kaplan-Meier curve showed a better survival for patients in initial stages (40.72 mo) compared to those in advanced stages (28.6 mo) (P<0.01). Survival was also reduced in a statistically significant manner in patients with any degree of dysplasia in the adjacent margin (P<0.05). During univariate Cox regression analysis, it was observed that individuals with relapse had a higher risk (almost 9 times higher) [P<0.001; hazard ratio=8.91; 95% confidence interval (CI), 4.18-19.02]. During the Cox multivariate analysis for each unit of decrease in p16(INK4a), the risk increased by 1.06) (P<0.05; hazard ratio=0.94; 95% CI, 0.89-1.00). p16(INK4a) expression is reduced with advancing tumor stage and its gene silencing is associated with an increased risk of death.

Low prevalence of transcriptionally active human papilloma virus in Indian patients with HNSCC and leukoplakia

OBJECTIVES

In the present study, we comprehensively analyzed the prevalence of transcriptionally active human papilloma virus (HPV) in tissue samples of Indian patients with leukoplakia, predominantly hyperplastic lesions and head and neck squamous cell carcinoma (HNSCC). In addition, saliva samples from patients with HNSCC were screened for HPV detection.

STUDY DESIGN

P16 overexpression was analyzed by immunohistochemistry. Tissue samples of leukoplakia (n = 121) and HNSCC (n = 427) and saliva from patients with HNSCC (n = 215) were tested for HPV using nested polymerase chain reaction. Positive samples were sequenced for subtyping. The presence of HPV E6/E7 mRNA was confirmed by RNA in situ hybridization.

RESULTS

P16 expression and HPV DNA were not detected in any of the leukoplakia specimens. Of the 427 HNSCC tumors, 9 showed p16 overexpression and 7/427 cases were positive for HPV16 DNA, in saliva or tissue. E6/E7 mRNA positivity was observed in 8 HNSCC samples, primarily from patients with no habit of tobacco consumption. The prevalence of high-risk HPV was restricted to oropharynx and larynx, with very little concordance between p16 overexpression and HPV positivity. All patients with HPV-positive saliva samples had transcriptionally active HPV present in their tumors.

CONCLUSION

The presence of HPV DNA does not necessarily reflect transcriptionally active virus in tumors; hence, it is important to consider this fact while categorizing HPV-associated tumors.

Molecular Aspects of Head and Neck Cancer Therapy

In spite of a rapidly expanding understanding of head and neck tumor biology and optimization of radiation, chemotherapy, and surgical treatment modalities, head and neck squamous cell carcinoma (HNSCC) remains a major cause of cancer-related morbidity and mortality. Although our biologic understanding of these tumors had largely been limited to pathways driving proliferation, survival, and differentiation, the identification of HPV as a major driver of HNSCC and genomic sequencing analyses has dramatically influenced our understanding of tumor biology and approach to therapy. Here, we summarize molecular aspects of HNSCC biology and identify promising areas for potential diagnostic and therapeutic agents.

Clinical implications of epigenetic regulation in oral cancer

Oral cancer is a high incidence cancer which is of major public health concern in India being the most common cancer in males and fifth most common cancer in females in India, contributing to 26% of the global oral cancer burden. The major risk factors of oral cancer are tobacco, alcohol and high risk Human Papilloma Virus type 16/18. However, only 3-12% of the high risk individuals with dysplasia develop oral cancer. Thus, individual genomic variants representing the genomic constitution and epigenetic alterations play a critical role in the development of oral cancer. Extensive epigenetic studies on the molecular lesions including oncogenes, tumor suppressor genes, genes associated with apoptosis, DNA damage repair have been reported. The current review highlights epigenetic regulation with a focus on molecular biomarkers and epidrug therapy in oral cancer. Epigenetic regulation by hypermethylation, histone modifications and specific microRNAs are often associated with early events and advanced stages in oral cancer, and thus indicate epidrug therapy for intervention. The presence of epigenetic marks in oral lesions, cancers and tumor associated mucosa emphasizes indications as biomarkers and epidrugs with therapeutic potential for better patient management.

Natural Compounds: DNA Methyltransferase Inhibitors in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is a multistep process which is modulated by several endogenous and environmental factors. Epigenetic changes have been found to be equally responsible for OSCC as genetic changes. A plethora of genes showing hypermethylation have been discovered in OSCC. Since these changes are reversible, a lot of emphasis is on using the natural compounds for their ability to cause demethylation which could lead to reactivation of the inactivated tumor suppressor genes. This review encompasses the promoter hypermethylation of tumor suppressor genes in OSCC and its possible reversal using natural compounds. In addition, new compounds which could be screened for their demethylating ability have also been proposed.

The protective effect of p16(INK4a) in oral cavity carcinomas: p16(Ink4A) dampens tumor invasion-integrated analysis of expression and kinomics pathways

A large body of evidence shows that p16(INK4a) overexpression predicts improved survival and increased radiosensitivity in HPV-mediated oropharyngeal squamous cell carcinomas.(OPSCC). Here we demonstrate that the presence of transcriptionally active HPV16 in oral cavity squamous cell carcinomas does not correlate with p16(INK4a) overexpression, enhanced local tumor immunity, or improved outcome. It is interesting that HPV-mediated oropharyngeal squamous cell carcinomas can be categorized as having a 'nonaggressive' invasion phenotype, whereas aggressive invasion phenotypes are more common in HPV-negative squamous cell carcinomas. We have developed primary cancer cell lines from resections with known pattern of invasion as determined by our validated risk model. Given that cell lines derived from HPV-mediated oropharyngeal squamous cell carcinomas are less invasive than their HPV-negative counterparts, we tested the hypothesis that viral oncoproteins E6, E7, and p16(INK4a) can affect tumor invasion. Here we demonstrate that p16(INK4a) overexpression in two cancer cell lines (UAB-3 and UAB-4), derived from oral cavity squamous cell carcinomas with the most aggressive invasive phenotype (worst pattern of invasion type 5 (WPOI-5)), dramatically decreases tumor invasiveness by altering expression of extracellular matrix remodeling genes. Pathway analysis integrating changes in RNA expression and kinase activities reveals different potential p16(INK4a)-sensitive pathways. Overexpressing p16(INK4a) in UAB-3 increases EGFR activity and increases MMP1 and MMP3 expression, possibly through STAT3 activation. Overexpressing p16(INK4a) in UAB-4 decreases PDGFR gene expression and reduces MMP1 and MMP3, possibly through STAT3 inactivation. Alternatively, ZAP70/Syk might increase MUC1 phosphorylation, leading to the observed decreased MMP1 expression.

Quantitative methodology is critical for assessing DNA methylation and impacts on correlation with patient outcome

BACKGROUND

DNA hypermethylation is reported as a frequent event and prognostic marker in head and neck squamous cell carcinomas (HNSCC). Methylation has been commonly assessed with non-quantitative methodologies, such as methylation-specific PCR (MSP). We investigated previously reported hypermethylated genes with quantitative methodology in oral tongue squamous cell carcinomas (OTSCC).

RESULTS

The methylation status of 12 genes in 115 OTSCC samples was assessed by one or more of three quantitative analyses: methylation sensitive high resolution melting (MS-HRM), sensitive-melting analysis after real time-methylation specific PCR (SMART-MSP), and bisulfite pyrosequencing. In contrast to much of the literature, either no or infrequent locus-specific methylation was identified by MS-HRM for DAPK1, RASSF1A, MGMT, MLH1, APC, CDH1, CDH13, BRCA1, ERCC1, and ATM. The most frequently methylated loci were RUNX3 (18/108 methylated) and ABO (22/107 methylated). Interrogation of the Cancer Genome Atlas (TCGA) HNSCC cohort confirmed the frequency of significant methylation for the loci investigated. Heterogeneous methylation of RUNX3 (18/108) and ABO (22/107) detected by MS-HRM, conferred significantly worse survival (P = 0.01, and P = 0.03). However, following quantification of methylation levels using pyrosequencing, only four tumors had significant quantities (>15%) of RUNX3 methylation which correlated with a worse patient outcome (P <0.001), while the prognostic significance of ABO hypermethylation was lost. RUNX3 methylation was not prognostic for the TCGA cohort (P = 0.76).

CONCLUSIONS

We demonstrated the critical need for quantification of methylation levels and its impact on correlative analyses. In OTSCC, we found little evidence of significant or frequent hypermethylation of many loci reported to be commonly methylated. It is likely that previous reports have overestimated the frequency of significant methylation events as a consequence of the use of non-quantitative methodology.

A pilot study evaluating genetic alterations that drive tobacco- and betel quid-associated oral cancer in Northeast India

The susceptibility of an individual to oral cancer is mediated by genetic factors and carcinogen-exposure behaviors such as betel quid chewing, tobacco use, and alcohol consumption. This pilot study was aimed to identify the genetic alteration in 100 bp upstream and downstream flanking regions in addition to the exonic regions of 169 cancer-associated genes by using Next Generation sequencing with aim to elucidate the molecular pathogenesis of tobacco- and betel quid-associated oral cancer of Northeast India. To understand the role of chemical compounds present in tobacco and betel quid associated with the progression of oral cancer, single nucleotide polymorphisms (SNPs) and insertion and deletion (Indels) found in this study were analyzed for their association with chemical compounds found in tobacco and betel quid using Comparative Toxogenomic Database. Genes (AR, BRCA1, IL8, and TP53) with novel SNP were found to be associated with arecoline which is the major component of areca nut. Genes (BARD1, BRCA2, CCND2, IGF1R, MSH6, and RASSF1) with novel deletion and genes (APC, BRMS1, CDK2AP1, CDKN2B, GAS1, IGF1R, and RB1) with novel insertion were found to be associated with aflatoxin B1 which is produced by fermented areca nut. Genes (ADH6, APC, AR, BARD1, BRMS1, CDKN1A, E2F1, FGFR4, FLNC, HRAS, IGF1R, IL12B, IL8, NBL1, STAT5B, and TP53) with novel SNP were found to be associated with aflatoxin B1. Genes (ATM, BRCA1, CDKN1A, EGFR, IL8, and TP53) with novel SNP were found to be associated with tobacco specific nitrosamines.

Promoter region hypermethylation and mRNA expression of MGMT and p16 genes in tissue and blood samples of human premalignant oral lesions and oral squamous cell carcinoma

Promoter methylation and relative gene expression of O(6)-methyguanine-DNA-methyltransferase (MGMT) and p16 genes were examined in tissue and blood samples of patients with premalignant oral lesions (PMOLs) and oral squamous cell carcinoma (OSCC). Methylation-specific PCR and reverse transcriptase PCR were performed in 146 tissue and blood samples from controls and patients with PMOLs and OSCC. In PMOL group, significant promoter methylation of MGMT and p16 genes was observed in 59% (P = 0.0010) and 57% (P = 0.0016) of tissue samples, respectively, and 39% (P = 0.0135) and 33% (P = 0.0074) of blood samples, respectively. Promoter methylation of both genes was more frequent in patients with OSCC, that is, 76% (P = 0.0001) and 82% (P = 0.0001) in tissue and 57% (P = 0.0002) and 70% (P = 0.0001) in blood, respectively. Significant downregulation of MGMT and p16 mRNA expression was observed in both tissue and blood samples from patients with PMOLs and OSCC. Hypermethylation-induced transcriptional silencing of MGMT and p16 genes in both precancer and cancer suggests important role of these changes in progression of premalignant state to malignancy. Results support use of blood as potential surrogate to tissue samples for screening or diagnosing PMOLs and early OSCC.

Frequency of genetic and epigenetic alterations of p14ARF and p16INK4A in head and neck cancer in a Hungarian population

Occurrence of genetic and epigenetic alterations affecting p14ARF and p16INK4A were investigated in tumour samples of 37 oral (OSCC) and 28 laryngeal squamous cell cancer (LSCC) patients, and compared to exfoliated buccal epithelial cells of 68 healthy controls. Presence of deletions and mutations/polymorphisms affecting exons were examined using sequencing. Methylation status of promoters was assessed by methylation-specific PCR. Chi-square and Fisher's exact tests were used to compare frequency of events. Exon deletions were found in four controls, one OSCC and 22 LSCC patients; the latter significantly differed from controls (p < 0.001). Only two mutations (T24610A and C24702A) were in p16 exon 1 of two OSCC patients. Polymorphisms G28575A (Ala140Thr), G31292C (C540G) and G28608A were found in both patient groups. The p14 promoter was unmethylated in 86.7 % of OSCC and in 85.7 % of LSCC patients; for the p16 promoter these rates were 69.0 % and 76.2 % for OSCC and LSCC patients, respectively. Combining the two patient groups, unmethylated promoter was significantly less frequent in case of both p14 and p16 (p = 0.043 and p = 0.001, respectively) compared to the control group. In summary, exon deletion may be important in LSCC, while promoter methylation was relatively frequent in both patient groups.

The mutational spectrum of squamous-cell carcinoma of the head and neck: targetable genetic events and clinical impact

Squamous-cell cancer of the head and neck (SCCHN) represents a heterogeneous disease entity, with various etiological factors implicated in the genesis of distinct molecular subsets of tumors, which exhibit different biological and clinical behavior. Treatment of SCCHN is expected to change in the next decade as targeted therapies continue to make strides. Recently, next-generation sequencing studies conducted on ∼190 SCCHN specimens shed light into the molecular pathogenesis of the disease. These studies discovered mutations in genes involved in the differentiation program of squamous epithelium and the Notch/p63 axis (such as NOTCH1, TP63 and FBXW7), and validated genetic alterations derived from previous studies (such as mutations in TP53, CDKN2A, PIK3CA, CCND1 and HRAS) as driver genetic events in SCCHN neoplastic transformation. More recently, comprehensive data from The Cancer Genome Atlas (TCGA) project on 306 SCCHN specimens provided further insight into SCCHN inherent molecular complexity, identifying novel significantly mutated genes, including FAT1, MLL2, TGFRBR2, HLA-A, NFE2l2 and CASP8. In this article, we provide an overview of the mutational spectrum of SCCHN, with emphasis on the clinical implementation of this knowledge. We also discuss the potential integration of new data within the framework of precision cancer medicine.

p16INK4A and p14ARF gene promoter hypermethylation as prognostic biomarker in oral and oropharyngeal squamous cell carcinoma: a review

Head and neck squamous cell carcinoma is a heterogeneous group of tumors with each subtype having a distinct histopathological and molecular profile. Most tumors share, to some extent, the same multistep carcinogenic pathways, which include a wide variety of genetic and epigenetic changes. Epigenetic alterations represent all changes in gene expression patterns that do not alter the actual DNA sequence. Recently, it has become clear that silencing of cancer related genes is not exclusively a result of genetic changes such as mutations or deletions, but it can also be regulated on epigenetic level, mostly by means of gene promoter hypermethylation. Results from recent studies have demonstrated that DNA methylation patterns contain tumor-type-specific signatures, which could serve as biomarkers for clinical outcome in the near future. The topic of this review discusses gene promoter hypermethylation in oral and oropharyngeal squamous cell carcinoma (OSCC). The main objective is to analyse the available data on gene promoter hypermethylation of the cell cycle regulatory proteins p16^INK4A and p14^ARF and to investigate their clinical significance as novel biomarkers in OSCC. Hypermethylation of both genes seems to possess predictive properties for several clinicopathological outcomes. We conclude that the methylation status of p16^INK4A is definitely a promising candidate biomarker for predicting clinical outcome of OSCC, especially for recurrence-free survival.

BCL6 overexpression is associated with decreased p19 ARF expression and confers an independent prognosticator in gallbladder carcinoma

B cell lymphoma 6 (BCL6) is a protein that is vital for lymphogenesis. Its expression has been well established in lymphoma, especially in diffuse large B-cell lymphoma. Its role in carcinogenesis is less well understood. Previous study shows that BCL6 expression may regulate p19 functions, an important regulator for the p53 pathway. No prior study has attempted to evaluate the significance of BCL6 and p19(ARF) expression in a large cohort of patients with gallbladder carcinomas (GBCs). We selected 164 patients with GBC and performed immunostains for BCL6 and p19(ARF). BCL6 expression and p19(ARF) expression were evaluated using a histochemical score (H-score). We then correlated the results with various clinicopathological factors, disease-specific survival (DSS), and disease-free survival (DFS). BCL6 overexpression was significantly associated with high pT status, high TNM stage, higher histological grade (p = 0.029), vascular invasion, perineurial invasion, high Ki-67 labeling index, and low p19 expression. Importantly, BCL6 overexpression in GBC was strongly associated with worse DSS (p < 0.0001) and DFS (p < 0.0001) in the univariate analysis, and remained independently predictive of adverse outcomes (p = 0.001, hazard ratio (H.R.) = 3.098 for DSS; p = 0.002, H.R. = 2.255 for DFS). Low p19(ARF) expression was correlated with a poor DSS (p = 0.0144) and DFS (p = 0.0032) in the univariate analysis but was not prognosticatory in the multivariate analysis. In GBC, BCL6 overexpression correlated with adverse phenotypes and decreased p19(ARF) expression. BCL6 overexpression also independently predicts worse DSS and DFS, suggesting it has a role in tumorigenesis or carcinogenesis and could be a potential prognostic indicator in GBC.

Downregulation of KLF8 expression by shRNA induces inhibition of cell proliferation in CAL27 human oral cancer cells

OBJECTIVES

KLF8 is a member of KLF transcription factors which play an important tolr in oncogenesis. It is barely expressed in normal human epithelial cells but highly overexpressed in several types of human cancer cell lines. In the present study, we investigate the role of KLF8 in oral cancer and the effects of KLF8 knockdown via lentivirus mediated siRNA infection in human adenosquamos carcinoma CAL 27 cells.

STUDY DESIGN

We developed a vector-based siRNA expression system that can induce RNAi in CAL 27 oral cancer cells. Downregulation of KLF8 was confirmed by evaluating GFP expressions, RT-PCR and western blot analysis. Finally, the effects of KLF8 downregulation were analyzed by MTT assay and colony formation assays.

RESULTS

The expression levels of KLF8 mRNA and proteins are reduced in CAL 27 cells that transfected with 21-nt siRNA against KLF8. Lentivirus-mediated silencing of KLF8 reduces cell proliferation and colonies number, thereby indicating the role of KLF8 in cell proliferation and tumorigenesis.

CONCLUSIONS

These results strongly suggest that KLF8 is essential for growth of CAL 27 cancer cells. A better understanding of KLF8 function and processing may provide novel insights into the clinical therapy of oral cancer.

The Prognostic Value of p16 Hypermethylation in Cancer: A Meta-Analysis

Background

The prognostic value of p16 promoter hypermethylation in cancers has been evaluated for several years while the results remain controversial. We thus performed a systematic review and meta-analysis of studies assessing the impact of p16 methylation on overall survival (OS) and disease-free survival (DFS) to clarify this issue.

Methods

We searched Pubmed, Embase and ISI web of knowledge to identify studies on the prognostic impact of p16 hypermethylation in cancers. A total of 6589 patients from 45 eligible studies were included in the analysis. Pooled hazard ratios (HRs) with 95% confidence interval (95% CI) were calculated to estimate the effect using random-effects model.

Results

The analysis indicated that p16 hypermethylation had significant association with poor OS of non-small cell lung cancer (NSCLC) (HR 1.74, 95% CI: 1.36–2.22) and colorectal cancer (CRC) (HR 1.80; 95% CI 1.27–2.55). Moreover, the significant correlation was present between p16 hypermethylation and DFS of NSCLC (HR 2.04, 95% CI: 1.19–3.50) and head and neck cancer (HR 2.24, 95% CI: 1.35–3.73). Additionally, in the analysis of the studies following REMARK guidelines more rigorously, p16 hypermethylation had unfavorable impact on OS of NSCLC (HR 1.79, 95% CI: 1.35–2.39) and CRC (HR 1.96, 1.16–3.34), and on DFS of NSCLC (HR 2.12, 95% CI: 1.21–3.72) and head and neck cancer (HR 2.24, 95% CI: 1.35–3.73).

Conclusions

p16 hypermethylation might be a predictive factor of poor prognosis in some surgically treated cancers, particularly in NSCLC.

Aberrant DNA methylation of ESR1 and p14ARF genes could be useful as prognostic indicators in osteosarcoma

Osteosarcoma (OS) is the eighth most common form of childhood and adolescence cancer. Approximately 10%–20% of patients present metastatic disease at diagnosis and the 5-year overall survival remains around 70% for nonmetastatic patients and around 30% for metastatic patients. Metastatic disease at diagnosis and the necrosis grade induced by preoperative treatment are the only well-established prognostic factors for osteosarcoma. The DNA aberrant methylation is a frequent epigenetic alteration in humans and has been described as a molecular marker in different tumor types. This study evaluated the DNA aberrant methylation status of 18 genes in 34 OS samples without previous chemotherapy treatment and in four normal bone specimens and compared the methylation profile with clinicopathological characteristics of the patients. We were able to define a three-gene panel (AIM1, p14ARF, and ESR1) in which methylation was correlated with OS cases. The hypermethylation of p14ARF showed a significant association with the absence of metastases at diagnoses, while ESR1 hypermethylation was marginally associated with worse overall survival. This study demonstrated that aberrant promoter methylation is a common event in OS and provides evidence that p14ARF and ESR1 hypermethylation could be useful as a prognostic indicator for this disease.

Epigenetic mechanisms in oral carcinogenesis

Dysregulation of gene expression is a frequent occurrence in oral squamous cell carcinoma (OSCC). However, accumulating evidence suggests that in contrast to genetics, epigenetic modifications consisting of aberrant DNA methylation, histone modifications and altered expression of miRNAs induce OSCC tumorigenesis and perhaps play a more central role in the evolution and progression of this disease. The unifying theme among these three epigenetic mechanisms remains the same, which is aberrant regulation of gene expression. In this article, we provide a comprehensive review of the impact of epigenetics on oral tumorigenesis with a systematic report on aberrant DNA methylation, histone modifications and miRNA regulation in the pathogenesis of OSCC. We provide insights into recent studies on the prospect of biomarkers for early detection and indication of disease recurrence, and novel treatment modalities.

Head and neck cancer: from anatomy to biology

The 20th century saw great advances in anatomy-based (surgery and radiotherapy) and chemotherapy approaches for treating head and neck squamous cell carcinoma (HNSCC) and improving quality of life (QoL). However, despite these advances, the survival rate in HNSCC remains at ∼50%. Front-line treatments often cause severe toxicity and debilitating long-term impacts on QoL. In recent decades, dramatic advances have been made in our knowledge of fundamental tumor biology and signaling pathways that contribute to oncogenesis and cancer progression. These insights are presenting unprecedented opportunities to develop more effective and less toxic treatments that are specific to particular molecular targets. This review discusses some of the major, potentially targetable, molecular pathways associated with head and neck carcinogenesis. We present the general mechanism underlying the functional components for each signaling pathway, discuss how these components are aberrantly regulated in HNSCC and describe their potential as therapeutic targets. We have restricted our discussion to "drug-able targets" such as oncogenes including those associated with HPV, tumor hypoxia and microRNAs and present these changes in the context of HNSCC patient care. The specific targeting of these pathways to achieve cancer control/remission and reduce toxicity is now challenging conventional treatment paradigms in HNSCC. This new "biologic era" is transforming our ability to target causal pathways and improve survival outcomes in HNSCC.

Promoter hypermethylation in primary squamous cell carcinoma of the oral cavity and oropharynx: a study of a Brazilian cohort

Epigenetic silencing of cancer-related genes plays an important role in oral/oropharyngeal squamous cell carcinoma (OSCC). We evaluated promoter hypermethylation of 4 cancer-related genes in OSCCs of a Brazilian cohort and determined its relationship with exposure to alcohol, tobacco, HPV infection and clinicopathological parameters. CDKN2A (cyclin-dependent kinase inhibitor 2A or p16), SFN (stratifin or 14-3-3 σ), EDNRB (endothelin receptor B) and RUNX3 (runt-related transcript factor-3) had their methylation patterns evaluated by MSP analysis in OSCC tumors (n = 45). HPV detection was carried out by PCR/RFLP. Aberrant methylation was detected in 44/45 (97.8 %) OSCC; 24.4 % at CDKN2A, 77.8 % at EDNRB, 17.8 % at RUNX3 and 97.8 % at SFN gene. There was no significant association between methylation patterns and clinical parameters. HPV (subtype 16) was detected in 3 out of 45 patients (6 %). Our findings indicate that HPV infection is uncommon and methylation is frequent in Brazilian OSCCs, however, EDNRB and SFN gene methylation are not suitable OSCC biomarkers due to indistinct methylation in tumoral and normal samples. In contrast, CDKN2A and RUNX3 genes could be considered differentially methylated genes and potential tumor markers in OSCCs.

The molecular pathogenesis of head and neck squamous cell carcinoma

Squamous cell carcinoma of the head and neck (HNSCC) is a relatively common human cancer characterized by high morbidity, high mortality, and few therapeutic options outside of surgery, standard cytotoxic chemotherapy, and radiation. Although the most important risk factors are tobacco use and alcohol consumption, the disease is also linked to infection with high-risk types of human papilloma viruses (HPVs). Recent genetic analyses have yielded new insights into the molecular pathogenesis of this disease. Overall, while somatic activating mutations within classical oncogenes including PIK3CA and RAS occur in HNSCC, they are relatively uncommon. Instead genetic data point to a contribution of multiple tumor suppressor pathways, including p53, Rb/INK4/ARF, and Notch, in tumor initiation, progression, and maintenance. The increasingly refined knowledge of HNSCC genetics, combined with ever-more-sophisticated animal models and newer drug targeting strategies, should promote novel therapeutic approaches and improved disease outcomes.

Methylation-mediated molecular dysregulation in clinical oral malignancy

Herein we provide a concise review of the state of methylation research as it pertains to clinical oral cancerous and precancerous tissues. We provide context for ongoing research efforts in this field and describe technologies that are presently being applied to analyze clinical specimens. We also discuss the various recurrent methylation changes that have been reported for oral malignancy (including those genes frequently silenced by promoter methylation and the small RNAs with activity modulated by methylation changes) and describe surrogate disease markers identified via epigenetic analysis of saliva and blood specimens from patients with oral cancer.

Combined cytoplasmic and membranous EGFR and p53 overexpression is a poor prognostic marker in early stage oral squamous cell carcinoma

OBJECTIVE

Our aim was to evaluate the expression of several molecules that regulate growth, the cell cycle and signalling pathways including EGFR, p53, p16 and p27 in oral squamous cell carcinomas (OSCC). We examined their utility as prognostic markers by relating to clinicopathological characteristics and the clinical outcome.

PATIENTS AND METHODS

Using tissue microarray technology, we analysed 67 primary OSCC and examined immunohistochemical expression of EGFR, p53, p16 and p27. Multivariate analysis was conducted to examine their role in survival.

RESULTS

Many of the markers were highly expressed in these cancers. Membranous EGFR expression in 95.2%, both membrane and cytoplasm expression in 35%, p53 expression in 61.6%, p27 expression in 89.5% and p16 expression in 27.9% of cases. In the multivariate analysis, independent prognostic influence of a lower overall survival was determined only for advanced tumour stage (P < 0.001), p53 overexpression (P = 0.004), EGFR cytoplasm and membrane co-expression location (P = 0.002) and p16 reduced expression (P = 0.002). When considering a subgroup of early stage tumours, p53 overexpression (P = 0.028) and combined membranous and cytoplasm EGFR co-expression (P = 0.039) were indicators of a lower overall survival. For disease-free survival, in addition to these three factors, the histological grade (P = 0.011) showed independent prognostic values.

CONCLUSION

The independent value of EGFR subcellular location (cytoplasm and membrane) and p53 overexpression in overall survival even in early stages of OSCC suggests that these markers may serve as reliable biological markers to identify high-risk subgroups and to guide therapy.

Epigenome and DNA methylation in oral squamous cell carcinoma

Epigenetics studies and defines inherited changes in gene expression that are not encoded in the DNA sequence. The most studied epigenetic change in mammalian DNA is cytosine methylation in CpG dinucleotide areas. The other main group in epigenetic changes includes the posttranslational modifications of histones, mainly phosphorylation, deacetylation changes, and in the ubiquitinylation status. Oral squamous cell carcinoma is the most common malignancy of the oral cavity, and epigenetic changes are very common, as described in this chapter. Alterations in the DNA methylation status resulting from exposure to environmental stress agents have been documented even before birth. Although many epigenetic markers are potentially reversible, the mechanism still remains unclear and many epigenetic changes persist across cell lines and the life of the organism.

Promoter methylation and loss of p16(INK4a) gene expression in head and neck cancer

BACKGROUND

Silencing of tumor suppressor genes plays a vital role in head and neck carcinogenesis. In this study we aimed to evaluate aberrant p16(INK4a) gene promoter methylation in patients with head and neck cancer.

METHODS

Methylation of the gene was investigated by bisulfite modification/methylation-specific polymerase chain reaction and gene expression levels were analyzed by quantitative reverse transcription-polymerase chain reaction in tumors and matched normal tissue samples from Turkish patients with head and neck cancer.

RESULTS

The promoter region of the p16(INK4a) gene was methylated in 67.5% and 28.6% of the primary tumors and the corresponding normal tissue, respectively. This difference was highly significant. In concordance, p16(INK4a) gene expression was downregulated in 67.5% of the tumor samples. Methylation and the absence of expression in the tumors were observed in 48% of the patients.

CONCLUSIONS

Our data indicate that methylation of the p16(INK4a) gene is a frequent event in primary head and neck cancer and that it plays a major role in the silencing of p16(INK4a) gene expression during tumor development.

Role of DNA methylation in head and neck cancer

Head and neck cancer (HNC) is a heterogenous and complex entity including diverse anatomical sites and a variety of tumor types displaying unique characteristics and different etilogies. Both environmental and genetic factors play a role in the development of the disease, but the underlying mechanism is still far from clear. Previous studies suggest that alterations in the genes acting in cellular signal pathways may contribute to head and neck carcinogenesis. In cancer, DNA methylation patterns display specific aberrations even in the early and precancerous stages and may confer susceptibility to further genetic or epigenetic changes. Silencing of the genes by hypermethylation or induction of oncogenes by promoter hypomethylation are frequent mechanisms in different types of cancer and achieve increasing diagnostic and therapeutic importance since the changes are reversible. Therefore, methylation analysis may provide promising clinical applications, including the development of new biomarkers and prediction of the therapeutic response or prognosis. In this review, we aimed to analyze the available information indicating a role for the epigenetic changes in HNC.

p16(INK4a)/CDKN2 expression and its relationship with oral squamous cell carcinoma is our current knowledge enough?

Oral squamous cell carcinomas (OSCC) are the most common malignancy of the oral cavity and their multistep development requires the accumulation of multiple genetic and epigenetic alterations. Inactivation of p16(INK4a), encoded by the CDKN2 gene has been widely associated with this type of tumors. The purpose of this review is to elucidate the relationship between p16(INK4a) expression and the different clinical and pathological aspects of OSCC, analyze the variation in results between studies, detailing the described genetic/epigenetic alterations that result in gene silencing and the relationship between p16(INK4a) and HPV infection.

Promoter hypermethylation in Indian primary oral squamous cell carcinoma

We evaluated promoter hypermethylation of a panel of tumor suppressor genes as a means to detect epigenetic alterations in oral squamous cell carcinomas (OSCC) of Indian-origin and compare with North-American head and neck squamous cell carcinomas (HNSCC). Quantitative-methylation-specific PCR was used to investigate the promoter methylation status of DCC, EDNRB, p16(INK4a) and KIF1A in 92 OSCC, and compared to 48 paired normal tissues and 30 saliva and sera samples from healthy control subjects. Aberrant methylation of at-least one of these genes was detected in 74/92 (80.4%) OSCC; 72.8% at EDNRB, 71.7% at KIF1A, 47.8% at p16(INK4a) and 58.7% at DCC; and in 5 of 48 (10.4%) normal oral tissues. None of the saliva and sera samples from controls exhibited DNA methylation in these four target genes. Thirty-two of 72 node positive cases harbored p16(INK4a) and DCC hypermethylation (p = 0.005). Thus, promoter hypermethylation in genes analyzed herein is a common event in Indian OSCC and may represent promising markers for the molecular staging of OSCC patients. We found higher frequency of p16(INK4a) methylation (47.8%) in this Indian cohort in comparison with a North-American cohort (37.5%). In conclusion, aberrant methylation of EDNRB, KIF1A, DCC and p16(INK4a) genes is a common event in Indian OSCC, suggesting that epigenetic alterations of these genes warrant validation in larger studies for their potential use as biomarkers.

CDKN2A but not TP53 mutations nor HPV presence predict poor outcome in metastatic squamous cell carcinoma of the skin

Genetic alterations in metastatic cutaneous squamous cell carcinoma (CSCC) which might serve as prognostic biomarkers are not well investigated. We investigated the mutation status and protein expression of the CDKN2A (INK4a-ARF) and TP53 genes in metastatic CSCCs and correlated this with clinicopathological variables, HPV presence, and survival data. Sequence analysis was performed on formalin-fixed and paraffin-embedded tissue of 35 metastases and their primary tumors, and was correlated with immunohistochemical stainings for p53, p16 and p14. Beta-PV and alpha-PV DNA was detected using PCR-based assays. Kaplan-Meier and Cox regression methods were used for survival assessment. CDKN2A was mutated in 31% of the metastases and their primary tumors, while the TP53 gene was mutated in 51% of the metastases. P53 protein expression was significantly associated with missense type of mutations (p = 0.002). No persistent HPV types were detected. CDKN2A mutations were significantly associated with disease-specific death (p = 0.001). A significant difference was observed in disease-specific survival between patients with or without a CDKN2A mutation (p = 0.010), while this was not the case for TP53. At univariate Cox's regression analysis tumor size (p = 0.010), invasion depth (p = 0.030) and CDKN2A mutations (p = 0.040) were significantly related to shorter disease-specific survival. At multivariate Cox's regression only tumor size had an adverse effect on survival (p = 0.002). In conclusion, our study indicates that the CDKN2A mutation status might be of prognostic value in metastatic CSCCs. In most cases, CDKN2A and TP53 mutations are early genetic events in CSCC tumorigenesis. The possible role of HPV in metastatic CSCC needs further exploration.