DNA studies underestimate the major role ofCDKN2A inactivation in oral and oropharyngeal squamous cell carcinomas

Impact of tobacco smoking on oral cancer genetics-A next-generation sequencing perspective

This study identified a total of 28 genetic loci (comprising 31 genes), which were found to be altered in oral cancer patients having a habit of tobacco smoking. Three loci, that is, 17p13.1 (TP53), 9p21.3 (CDKN2A), and 9q34.3 (NOTCH1) were found to be modified and common in three records whereas one locus, that is, 3q26.32 (PIK3CA) was found to be modified and common in two records. This study suggests that oral cancer patients should be categorized into different subgroups based on (i) genetic signatures, and (ii) smoking status, then the treatment strategies for each group should be precisely defined.

Human Papillomavirus Detected in Oropharyngeal Cancers from Chilean Subjects

High-risk human papillomaviruses (HR-HPV) are the causal agents of an important subset of oropharyngeal cancers that has increased considerably in incidence in recent years. In this study, we evaluated the presence of HPV in 49 oropharyngeal cancers from Chilean subjects. The presence of HPV DNA was analyzed by conventional PCR, the genotypes were identified through sequencing, and the expression of E6/E7 transcripts was evaluated by a reverse transcriptase polymerase chain reaction (RT-PCR). Additionally, to determine p16 expression—a surrogate marker for oncogenic HPV infection—a tissue array was constructed for immunohistochemistry (IHC). HPV was detected in 61.2% of oropharyngeal carcinomas, the most prevalent genotype being HPV16 (80%). E6 and E7 transcripts were detected in 91.6% and 79.1% of the HPV16-positive specimens, respectively, demonstrating functional HPV infections. Furthermore, p16 expression was positive in 58.3% of cases. These findings show a high prevalence of HR-HPV in oropharyngeal tumors from Chile, suggesting the necessity of additional studies to address this growing public health concern.

Expression and role of p16 and GLUT1 in malignant diseases and lung cancer: A review

Non‐small cell lung cancer (NSCLC) is the leading cause of cancer death and in most cases it is often diagnosed at an advanced stage. Many genetic and microenvironmental factors are able to modify the cell cycle inducing carcinogenesis and tumor growth. Among the metabolic and genetic factors that come into play in carcinogenesis and tumor cell differentiation and growth there are two different proteins that should be considered which are glucose transporters (GLUTs) and p16^INK4 The first are glucose transporters which are strongly involved in tumor metabolism, notably accelerating cancer cell metabolism both in aerobic and anaerobic conditions. There are different subtypes of GLUT family factors of which GLUT 1 is the most important and widely expressed. By contrast, p16 is mainly a tumor‐suppressor protein that acts on cyclin‐dependent kinase favoring cell cycle arrest in the G1 phase. Our search focused on the action of the aforementioned factors.

Molecular mechanisms underlying gliomas and glioblastoma pathogenesis revealed by bioinformatics analysis of microarray data

The aim of this study was to identify key genes associated with gliomas and glioblastoma and to explore the related signaling pathways. Gene expression profiles of three glioma stem cell line samples, three normal astrocyte samples, three astrocyte overexpressing 4 iPSC-inducing and oncogenic factors (myc(T58A), OCT-4, p53DD, and H-Ras(G12V)) samples, three astrocyte overexpressing 7 iPSC-inducing and oncogenic factors (OCT4, H-Ras(G12V), myc(T58A), p53DD, cyclin D1, CDK4(RC24) and hTERT) samples and three glioblastoma cell line samples were downloaded from the ArrayExpress database (accession: E-MTAB-4771). The differentially expressed genes (DEGs) in gliomas and glioblastoma were identified using FDR and t tests, and protein-protein interaction (PPI) networks for these DEGs were constructed using the protein interaction network analysis. The GeneTrail2 1.5 tool was used to identify potentially enriched biological processes among the DEGs using gene ontology (GO) terms and to identify the related pathways using the Kyoto Encyclopedia of Genes and Genomes, Reactome and WikiPathways pathway database. In addition, crucial modules of the constructed PPI networks were identified using the PEWCC1 plug-in, and their topological properties were analyzed using NetworkAnalyzer, both available from Cytoscape. We also constructed microRNA-target gene regulatory network and transcription factor-target gene regulatory network for these DEGs were constructed using the miRNet and binding and expression target analysis. We identified 200 genes that could potentially be involved in the gliomas and glioblastoma. Among them, bioinformatics analysis identified 137 up-regulated and 63 down-regulated DEGs in gliomas and glioblastoma. The significant enriched pathway (PI3K-Akt) for up-regulated genes such as COL4A1, COL4A2, EGFR, FGFR1, LAPR6, MYC, PDGFA, SPP1 were selected as well as significant GO term (ear development) for up-regulated genes such as CELSR1, CHRNA9, DDR1, FGFR1, GLI2, LGR5, SOX2, TSHR were selected, while the significant enriched pathway (amebiasis) for down-regulated gene such as COL3A1, COL5A2, LAMA2 were selected as well as significant GO term (RNA polymerase II core promoter proximal region sequence-specific binding (5) such as MEIS2, MEOX2, NR2E1, PITX2, TFAP2B, ZFPM2 were selected. Importantly, MYC and SOX2 were hub proteins in the up-regulated PPI network, while MET and CDKN2A were hub proteins in the down-regulated PPI network. After network module analysis, MYC, FGFR1 and HOXA10 were selected as the up-regulated coexpressed genes in the gliomas and glioblastoma, while SH3GL3 and SNRPN were selected as the down-regulated coexpressed genes in the gliomas and glioblastoma. MicroRNA hsa-mir-22-3p had a regulatory effect on the most up DEGs, including VSNL1, while hsa-mir-103a-3p had a regulatory effect on the most down DEGs, including DAPK1. Transcription factor EZH2 had a regulatory effect on the both up and down DEGs, including CD9, CHI3L1, MEIS2 and NR2E1. The DEGs, such as MYC, FGFR1, CDKN2A, HOXA10 and MET, may be used for targeted diagnosis and treatment of gliomas and glioblastoma.

Oncogenes and tumor suppressor genes in squamous cell carcinoma of the tongue in young patients

Objectives

The occurrence of squamous cell carcinoma of the tongue (SCCT) of young patients increased. There are still controversies about patient prognosis. The underlying molecular mechanisms remain unclear.

Methods

276 patients (66 ≤45, 210 >45 years) with SCCT were included. Clinical parameters and survival data were assessed. Oncogenes and tumor suppressors were analyzed via immunohistochemistry (p53, CXCR4, p16, EGFR) and qPCR (CDK4, CDKN2A, TP53, MDM2, AKT1, PIK3CA, NRAS, HRAS, KRAS, HGF, MET, EGF, ATM, BRCA1, E2F1, FHIT, RUNX3, STK11, BCL2, CTNNB1).

Results

The median overall survival was 142 (≤45 years) and 34 months (>45 years) (p < 0.0001; HR [95%CI]: 0.37 [0.30–0.58]). Disease specific survival in patients ≤45 years was with 181 months significantly higher than in patients >45 years (p < 0.0001; HR [95%CI]: 0.33 [0.26–0.57]). Immunhistochemistry visualized a comparable expression of analyzed proteins. QPCR demonstrated in patients ≤45 years a higher expression of genes that are associated with carcinogenesis (CTNNB1, STK11, CDKN2A, HGF, MET) as well as tumor suppressors that constitute an enhanced radio-sensitivity (ATM, BRCA1E2F1, FHIT).

Conclusion

Derogation of the WNT-CTNNB1-STK11 and CDKN2A-HGF-MET pathway can constitute the carcinogenesis, while the higher expression of radio-sensitizers ATM, BRCA1E2F1 and FHIT can explain the better OS/DSS in young patients.

Evaluation of immunohistochemical expression of p16 and presence of human papillomavirus in oral and oropharyngeal carcinoma

Carcinogenesis concerns several changes that eventually result in the inactivation of tumor suppressor genes and activation of protooncogenes, leading to loss of cell cycle control. Inactivation of p16 seems to be an early event in this process and occurs in approximately 80% of squamous cell carcinoma cases. The aims of this study were to evaluate the immunohistochemical expression of p16 protein in oral and oropharyngeal squamous cell carcinoma cases, with both the tumoral area itself and its surgical margin being analyzed (dysplastic areas and histologically normal epithelium adjacent to carcinoma), and to verify the presence of human papillomavirus (HPV) and its relation to p16 expression. Paraffin-embedded biopsy tissues from 26 patients, 13 with oral squamous cell carcinoma and 13 with oropharyngeal squamous cell carcinoma, comprised the analyzed samples. To detect HPV, a nested polymerase chain reaction test using PGMY 09/11 and GP5*/GP6* primers and visualization of the product on a 2% agarose gel was performed. Demographic data were obtained from medical records. The results showed low expression of p16 in the tumor area (38.46%), compared with surgical margins in the histologically normal epithelium (84.6%) and dysplastic areas (57.7%). These findings indicate the inactivation of p16 in the process of malignant transformation. The association described in the literature between expression of p16 and presence of HPV could not be verified in this study, because none of the cases was HPV positive.

Association between P16INK4a promoter methylation and HNSCC: a meta-analysis of 21 published studies

Background

The p16^INK4a is an important tumor suppressor gene (TSG) and aberrant methylation of promoter is known to be a major inactivation mechanism of the tumor suppressor and tumor-related genes. Aberrant TSG methylation was considered an important epigenetic silencing mechanism in the progression of head and neck squamous cell carcinoma (HNSCC). However, some studies have reported differences in the methylation frequencies of P^16INK4a promoter between cancer and the corresponding control group. Therefore, we conducted a meta-analysis to better identify the association.

Methods

PubMed, Ovid, ISI Web of Science, and EMBASE were searched to identify eligible studies to evaluate the association of p16^INK4a promoter methylation and HNSCC. Odds ratio (ORs) and 95% confidence intervals (95%CI) were calculated to evaluate the strength of association between p16^INK4a promoter methylation and HNSCC.

Results

A total of twenty-one studies with 1155 cases and 1017 controls were included in the meta-analysis. The frequencies of p16^INK4a promoter methylation in the cancer group were significantly higher than those in the control group (cancer group: median: 46.67%, range = 7.84%-95.12%; control group: median: 18.37%, range = 0–83.33%; respectively). The pooled odds ratio was 3.37 (95%CI = 2.32–4.90) in the cancer group versus the corresponding control group under the random-effects model.

Conclusion

This meta-analysis of 21 published studies identified that aberrant methylation of p16^INK4a promoter was found to be significantly associated with HNSCC.

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.

Senescent cancer-associated fibroblasts secrete active MMP-2 that promotes keratinocyte dis-cohesion and invasion

Background:

Previous studies have demonstrated that senescent cancer-associated fibroblasts (CAFs) derived from genetically unstable oral squamous cell carcinomas (GU-OSCC), unlike non-senescent CAFs from genetically stable carcinomas (GS-OSCC), promoted keratinocyte invasion in vitro in a paracrine manner. The mechanism by which this occurs is unclear.

Methods:

Previous work to characterise the senescent-associated secretory phenotype (SASP) has used antibody arrays, technology that is limited by the availability of suitable antibodies. To extend this work in an unbiased manner, we used 2D gel electrophoresis and mass spectroscopy for protein identification. Matrix metalloproteinases (MMPs) were investigated by gelatin zymography and western blotting. Neutralising antibodies were used to block key molecules in the functional assays of keratinocyte adhesion and invasion.

Results:

Among a variety of proteins that were differentially expressed between CAFs from GU-OSCC and GS-OSCC, MMP-2 was a major constituent of senescent CAF-CM derived from GU-OSCC. The presence of active MMP-2 was confirmed by gelatine zymography. MMP-2 derived from senescent CAF-CM induced keratinocyte dis-cohesion and epithelial invasion into collagen gels in a TGF-β-dependent manner.

Conclusions:

Senescent CAFs from GU-OSCC promote a more aggressive oral cancer phenotype by production of active MMP-2, disruption of epithelial adhesion and induction of keratinocyte invasion.

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.

Oncoapoptotic signaling and deregulated target genes in cancers: special reference to oral cancer

Cancer is a class of diseases characterized by uncontrolled cell growth. The development of cancer takes place in a multi-step process during which cells acquire a series of mutations that eventually lead to unrestrained cell growth and division, inhibition of cell differentiation, and evasion of cell death. Dysregulation of oncoapoptotic genes, growth factors, receptors and their downstream signaling pathway components represent a central driving force in tumor development. The detailed studies of signal transduction pathways for mechanisms of cell growth and apoptosis have significantly advanced our understanding of human cancers, subsequently leading to more effective treatments. Oral squamous cell carcinoma represents a classic example of multi-stage carcinogenesis. It gradually evolves through transitional precursor lesions from normal epithelium to a full-blown metastatic phenotype. Genetic alterations in many genes encoding crucial proteins, which regulate cell proliferation, differentiation, survival and apoptosis, have been implicated in oral cancer. As like other solid tumors, in oral cancer these genes include the ones coding for cell cycle regulators or oncoproteins (e.g. Ras, Myc, cyclins, CDKs, and CKIs), tumor suppressors (e.g. p53 and pRb), pro-survival proteins (e.g. telomerase, growth factors or their receptors), anti-apoptotic proteins (e.g. Bcl2 family, IAPs, and NF-kB), pro-apoptotic proteins (e.g. Bax and BH-3 family, Fas, TNF-R, and caspases), and the genes encoding key transcription factors or elements for signal transduction leading to cell growth and apoptosis. Here we discuss the current knowledge of oncoapoptotic regulation in human cancers with special reference to oral cancers.

Recurrence in oral and pharyngeal cancer is associated with quantitative MGMT promoter methylation

Background

Biomarkers that predict clinical response, tumor recurrence or patient survival are severely lacking for most cancers, particularly for oral and pharyngeal cancer. This study examines whether gene-promoter methylation of tumor DNA correlates with survival and recurrence rates in a population of patients with oral or pharyngeal cancer.

Methods

The promoter methylation status of the DNA repair gene MGMT and the tumor suppressor genes CDKN2A and RASSF1 were evaluated by methylation-specific PCR in 88 primary oral and pharyngeal tumors and correlated with survival and tumor recurrence. Quantitative MGMT methylation was also assessed.

Results

29.6% of the tumors presented with MGMT methylation, 11.5% with CDKN2A methylation and 12.1% with RASSF1 methylation. MGMT promoter methylation was significantly associated with poorer overall and disease-free survival. No differences in methylation status of MGMT and RASSF1 with HPV infection, smoking or drinking habits were observed. A significant inverse trend with the amount of MGMT methylation and overall and disease-free survival was observed (p_trend = 0.002 and 0.001 respectively).

Conclusion

These results implicate MGMT promoter methylation as a possible biomarker for oral and pharyngeal cancer prognosis. The critical role of MGMT in DNA repair suggests that defective DNA repair may be correlative in the observed association between MGMT promoter methylation and tumor recurrence. Follow-up studies should include further quantitative MSP-PCR measurement, global methylation profiling and detailed analysis of downstream DNA repair genes regulated by promoter methylation.

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

BACKGROUND

Oral cancer patients are found to have poor clinical outcome and high disease recurrence rate, in spite of an aggressive treatment regimen. The inactivation of INK4A/ARF loci is reported to be second to p53 inactivation in human cancers. The purpose of this study was to assess the prognostic significance of the molecular aberrations in the INK4A locus for effective identification of aggressive oral carcinoma cases needing alternate therapy.

MATERIALS AND METHODS

The study composed of 116 patients freshly diagnosed with oral carcinoma. The genetic and epigenetic status of the p16(INK4A) and p14(ARF) genes was evaluated. The relation between these genic alterations and different treatment end points, such as residual disease (initial response), disease recurrence, and overall survival, along with the standard clinical markers, were analyzed.

RESULTS

62% of the study cases had p16(INK4A) gene abnormalities, with deletion accounting for 33% and methylation for 29%. Alterations in p14(ARF) gene either by deletion (12%) and/or methylation (18%) were observed in 30% of the cases. p16(INK4A) deletion was associated with aggressive tumors, as evidenced by the nodal involvement of the disease. Low or absence of p16(INK4A) protein adversely affected the initial treatment response. Promoter methylation of p16(INK4A) was associated with increased disease recurrence and acts as an independent predictor for worse prognosis. Surprisingly, p14(ARF) methylation associated with lower recurrence rate in oral cancer patients with a good clinical outcome. Overall survival of these patients was associated with tumor size, nodal disease, and p16(INK4A) protein expression pattern. Our results indicate that p16(INK4A) and p14(ARF) alterations constitute a major molecular abnormality in oral cancer cases.

CONCLUSION

The molecular profile of INK4A/ARF locus, both at DNA and protein level, could be used as a prognostic biomarker for assessing the aggressiveness of disease in oral carcinoma patients. The study further shows the opposing clinical effect of these two genes, transcribed from the same locus, in oral cancer patients.

Molecular pathogenesis of oral squamous cell carcinoma: implications for therapy

The development of oral squamous cell carcinoma (OSCC) is a multistep process requiring the accumulation of multiple genetic alterations, influenced by a patient's genetic predisposition as well as by environmental influences, including tobacco, alcohol, chronic inflammation, and viral infection. Tumorigenic genetic alterations consist of two major types: tumor suppressor genes, which promote tumor development when inactivated; and oncogenes, which promote tumor development when activated. Tumor suppressor genes can be inactivated through genetic events such as mutation, loss of heterozygosity, or deletion, or by epigenetic modifications such as DNA methylation or chromatin remodeling. Oncogenes can be activated through overexpression due to gene amplification, increased transcription, or changes in structure due to mutations that lead to increased transforming activity. This review focuses on the molecular mechanisms of oral carcinogenesis and the use of biologic therapy to specifically target molecules altered in OSCC. The rapid progress that has been made in our understanding of the molecular alterations contributing to the development of OSCC is leading to improvements in the early diagnosis of tumors and the refinement of biologic treatments individualized to the specific characteristics of a patient's tumor.

Spindle assembly checkpoint and centrosome abnormalities in oral cancer

Like many solid tumours, oral squamous cell carcinomas (OSCC) invariably exhibit chromosomal instability (CIN) leading to aneuploidy. The mechanisms responsible for CIN in OSCC, however, are largely unknown. This study examined the fidelity of the spindle checkpoint, together with the number, structure and function of centrosomes in a series of well-characterised aneuploid immortal OSCC-derived cell lines that harbour p53 and p16(INK4A) defects. The spindle checkpoints were fully functional in 2 of 7 cell lines and attenuated in the remaining 5 cell lines. Overexpression of the spindle checkpoint protein, Cdc20, was observed in 2 of the cell lines with attenuated checkpoints. Defects in centrosome number, size and localisation were detected in 5 of the cell lines. Clonal cell populations contained cells with both normal and abnormal numbers of centrosomes, suggesting that the control of centrosome number may be inherently unstable in OSCC-derived cell lines. Centrosomal abnormalities were then examined in tissue samples of oral epithelial dysplasias and carcinomas. Abnormal centrosomes were detected in all the tissues examined albeit in a low percentage of cells (<1% to >5%). The percentage of cells containing centrosome abnormalities was significantly higher in the carcinomas than in the dysplasias (p<0.02) and in the poorly differentiated SCCs relative to their moderately differentiated (p<0.04) and well-differentiated (p<0.01) counterparts. We suggest that the genetic alterations associated with the development of the immortal phenotype, together with spindle checkpoint and centrosome defects, are responsible, albeit in part, for the complex karyotypes observed in OSCC. The presence of centrosome abnormalities in oral dysplasias raises the possibility that such defects might contribute to malignant progression.

Cell cycle dysregulation in oral cancer

The dysregulation of the molecular events governing cell cycle control is emerging as a central theme of oral carcinogenesis. Regulatory pathways responding to extracellular signaling or intracellular stress and DNA damage converge on the cell cycle apparatus. Abrogation of mitogenic and anti-mitogenic response regulatory proteins, such as the retinoblastoma tumor suppressor protein (pRB), cyclin D1, cyclin-dependent kinase (CDK) 6, and CDK inhibitors (p21(WAF1/CIP1), p27(KIP1), and p16(INK4a)), occur frequently in human oral cancers. Cellular responses to metabolic stress or genomic damage through p53 and related pathways that block cell cycle progression are also altered during oral carcinogenesis. In addition, new pathways and cell cycle regulatory proteins, such as p12(DOC-1), are being discovered. The multistep process of oral carcinogenesis likely involves functional alteration of cell cycle regulatory members combined with escape from cellular senescence and apoptotic signaling pathways. Detailing the molecular alterations and understanding the functional consequences of the dysregulation of the cell cycle apparatus in the malignant oral keratinocyte will uncover novel diagnostic and therapeutic approaches.

Advances in the biology of oral cancer

The incidence of oral cancer remains high and is associated with many deaths in both Western and Asian countries. Several risk factors for the development of oral cancer are now well known, including smoking, drinking and consumption of smokeless tobacco products. Genetic predisposition to oral cancer has been found in certain cases but its components are not yet entirely clear. In accordance with the multi-step theory of carcinogenesis, the natural history of oral cancer seems to gradually evolve through transitional precursor lesions from normal epithelium to a full-blown metastatic phenotype. A number of genomic lesions accompany this transformation and a wealth of related results has appeared in recent literature and is being summarized here. Furthermore, several key genes have been implicated, especially well-known tumor suppressors like the cyclin-dependent kinase inhibitors, TP53 and RB1 and oncogenes like the cyclin family, EGFR and ras. Viral infections, particularly with oncogenic HPV subtypes and EBV, can have a tumorigenic effect on oral epithelia and their role is discussed, along with potential therapeutic interventions. A brief explanatory theoretical model of oral carcinogenesis is provided and potential avenues for further research are highlighted.

Duration but not Intensity of Alcohol and Tobacco Exposure Predicts p16INK4A Homozygous Deletion in Head and Neck Squamous Cell Carcinoma

In tobacco-associated solid tumors, evidence suggests that the pattern of carcinogen exposure is related to the nature of somatic gene inactivation within crucial pathways, including the retinoblastoma (Rb) pathway. One somatic event in this pathway, homozygous deletion of the p16INK4A gene, is commonly observed in head and neck squamous cell carcinoma (HNSCC). Alcohol and tobacco are both well-established risk factors for HNSCC but there has been little characterization of the relationship of exposure to these carcinogens and inactivation of the p16INK4A gene. Hypothesizing that p16INK4A homozygous deletion is associated with tobacco and alcohol exposure, we investigated 330 consecutive HNSCC tumors. The odds ratio (OR) for p16INK4A homozygous deletion among alcohol consumers in the upper tertile (>43 years used) was 5.2 [95% confidence interval (95% CI), 2.1-12.8] as compared with those with < or = 43 years of alcohol consumption. Intensity of alcohol exposure, measured as average alcoholic drinks per week, was not associated with gene deletion. When we examined the distribution of duration of tobacco use, the OR for p16(INK4A) homozygous deletion was 1.3 (95% CI, 0.5-3.0) and 1.9 (95% CI, 0.9-4.0) for 29 to 39 years and >39 years of tobacco smoking, respectively, as compared with those that smoked < or = 28 years. As in the case of alcohol use, intensity of tobacco exposure (measured as packs per day) was not associated with gene deletion. Hence, the duration of alcohol use and duration of smoking, but not intensity of either, significantly predicted p16(INK4A) homozygous deletion in HNSCC.

Promoter methylation and inactivation of tumour-suppressor genes in oral squamous-cell carcinoma

Genetic alterations that lead to loss or changes in tumour-suppressor genes are known to contribute to oral carcinogenesis. Traditional molecular methods to detect such losses have relied on mutation analysis or deletion of the gene. However, epigenetic mechanisms could also contribute to silencing of tumour-suppressor genes. Methylation regions rich in CpG promoters prevent DNA transcription by changing the binding of histone complexes. The substantial contribution of methylation, specifically in oral squamous-cell carcinoma, is now being realised and investigated.

Dietary folate is associated withp16INK4A methylation in head and neck squamous cell carcinoma

Inactivation of the p16(INK4A) (CDKN2A) gene in the Rb pathway is among the most common somatic alterations observed in tobacco-related solid tumors, including head and neck squamous cell carcinoma (HNSCC). In addition, a low folate diet is an important risk factor for HNSCC. Decreased dietary folate in an animal model of hepatocellular carcinoma has been associated with the induction of epigenetic silencing of the p16(INK4A) gene. In an ongoing population-based study of HNSCC, we sought to extend this observation to human disease testing the hypothesis that p16(INK4A) methylation is associated with decreased dietary folate. We also investigated the association of methylation silencing with functional polymorphisms in the folate metabolism enzyme methylene tetrahydrofolate reductase (MTHFR). In 169 HNSCCs, the odds ratio for p16(INK4A) methylation among those with low dietary folate intake was 2.3 (95% CI = 1.1-4.8) when compared with those with high folate intake. Furthermore, this increased risk for epigenetic silencing at p16(INK4A) was modified by the MTHFR alleles previously associated with diminished serum folate levels. Hence, in HNSCC low dietary intake of folate is associated with p16(INK4A) methylation, and this relationship is modified by the MTHFR genotype. Our data provides important evidence for a mechanism of action of folate deficiency in cancer.

Homozygous deletions of CDKN2A caused by alternative mechanisms in various human cancer cell lines

The CDKN2A tumor-suppressor locus on chromosome band 9p21, which encodes p16(INK4A), a negative regulator of cyclin-dependent kinases, and p14(ARF1), an activator of TP53, is inactivated in many human cancers by point mutation, promoter hypermethylation, and, often, deletion. Homozygous deletions are unusually prevalent at this locus in very different human cancers. In the present study, we compared deletions in squamous cell carcinoma of the head and neck (SCCHN) cell lines to those in T-cell acute lymphatic leukemia (T-ALL), glioma, and bladder carcinoma (TCC) cell lines. Of 14 SCCHN lines, 10 showed homozygous deletions of CDKN2A, one displayed promoter hypermethylation with gene silencing, and one had a frameshift deletion in exon 2. Many deletion ends were in or proximal to the repetitive sequence clusters flanking the locus. Breakpoint junctions displayed variable microhomologies or insertions characteristic of DNA repair by nonhomologous end-joining. In general, deletions were much smaller in SCCHN than in TCC and glioma. In T-ALL, breakpoints were near consensus sites for recombination mediated by RAG (recombination activating genes) enzymes, and the structure of the junctions was consistent with this mechanism. We suggest that different mechanisms of CDKN2A deletion prevail in different human cancers. Aberrant RAG-mediated recombination may be responsible in T-ALL, and exuberant DNA repair by nonhomologous end-joining is the likely prevailing mechanism in SCCHN, but a distinct mechanism in TCC and glioma remains to be elucidated.

Oral cavity and esophageal carcinogenesis modeled in carcinogen-treated mice

PURPOSE

Squamous cell carcinoma of the oral cavity is one of the most common human neoplasms, and prevention of these carcinomas requires a better understanding of the carcinogenesis process and a model system in which cancer chemoprevention agents can be tested. We have developed a mouse model using the carcinogen 4-nitroquinoline 1-oxide (4-NQO) in the drinking water to induce tumorigenesis in the mouse oral cavity.

EXPERIMENTAL DESIGN

4-NQO was delivered by tongue painting or drinking water to two mouse strains, CBA and C57Bl/6. The incidences of oral cavity carcinogenesis were then compared. In addition, we examined the expression of some of the molecular markers associated with the process of human oral cavity and esophageal carcinogenesis, such as keratin (K) 1, K14, p16, and epidermal growth factor receptor, by immunohistochemistry.

RESULTS

After treatment with 4-NQO in the drinking water, massive tumors were observed on the tongues of both CBA and C57Bl/6 female mice. Pathological analyses indicated that flat squamous dysplasias, exophytic papillary squamous tumors (papillomas), and invasive squamous cell carcinomas were present. Immunohistochemistry analyses showed that 4-NQO changed the expression patterns of the intermediate filament proteins K14 and K1. K14 was expressed in the epithelial suprabasal layers, in addition to the basal layer, in tongues from carcinogen-treated animals. In contrast, control animals expressed K14 only in the basal layer. Moreover, we observed more bromodeoxyuridine staining in the tongue epithelia of 4-NQO-treated mice. Reduced expression of the cell cycle inhibitor, p16, was observed, whereas 4-NQO treatment caused an increase in epidermal growth factor receptor expression in the mouse tongues. Interestingly, similar features of carcinogenesis, including multiple, large (up to 0.5 cm) exophytic papillary squamous tumors and invasive squamous cell carcinomas, increased bromodeoxyuridine staining, and increased K14 expression, were also observed in the esophagi of 4-NQO-treated mice. However, no tumors were observed in the remainder of digestive tract (including the forestomach, intestine, and colon) or in the lungs or livers of 4-NQO-treated mice. These results indicate that this murine 4-NQO-induced oral and esophageal carcinogenesis model simulates many aspects of human oral cavity and esophageal carcinogenesis.

CONCLUSIONS

The availability of this mouse model should permit analysis of oral cavity and esophageal cancer development in various mutant and transgenic mouse strains. This model will also allow testing of cancer chemopreventive drugs in various transgenic mouse strains.

Immunohistochemical detection of a germline BRCA1 mutation in a breast and ovarian cancer family

Tumours from four individuals in a breast and ovarian cancer family with a known deleterious germline BRCA1 mutation, were analyzed using BRCA1 antibodies. In addition, we examined tumours from 96 female patients with early-onset breast cancer, who were not selected because of any family history. Paraffin-embedded tumour sections were examined by standard immunohistochemical analysis. Three familial tumours from BRCA1 carriers displayed focal negativity. This observation was not seen in a non-mutation carrier from the same family. It was found that 9/96 (9%) early-onset breast tumours had total BRCA1 negativity. In addition, 2/2 (100%) medullary breast carcinomas displayed negativity for both antibodies. Our results indicate that BRCA1 antibodies can discriminate between familial tumours with and without a deleterious mutation from one family. Further mutation studies in early-onset breast cancer group will be necessary to evaluate the use of immunohistochemistry as a rapid, initial screening technique to identify BRCA1 mutations.

[Genic alterations in oral and head and neck squamous cell carcinomas: analysis of international literature]

The development of oral and head and neck squamous cell carcinomas occurs in relation with multiple events including mainly: loss of cycle cell control, evasion from apoptosis, telomerase reactivation. Complex interactions between a set of molecules, cell cycle proteins, tumour suppressor genes, oncogenes and the telomerase, occur in the multiple step process of carcinogenesis. The 2 main ways of control of the cell cycle rely on 2 tumour suppressor genes: the P53 gene and the retinoblastoma gene or RB gene. One of the regulation pathways or the 2 regulation pathways are disabled during the development of oral and head and neck squamous cell carcinomas. Most of the time, the inactivation of the P53 pathway results from a loss of function of the p53 protein, secondary to mutation and/or deletion of the P53 gene; It may also result of the amplification of the MDM2 gene and of the inactivation of the arf protein. The RB pathway leads to cell proliferation by loss of the p16 protein, by amplification of the cyclin D1 gene and less frequently by mutation of the RB gene or loss of the retinoblastoma protein. In India and South-East Asia, the activation of RAS and MYC oncogenes appears to be related with the presence of specific carcinogens in snuff and tobacco. By blocking apoptosis, the Bcl2 protein seems to increase the resistance of tumours to radiotherapy and chemotherapy.

Human squamous cell carcinomas lose a mortality gene from chromosome 6q14.3 to q15

Normal human keratinocytes possess a finite replicative lifespan. Most advanced squamous cell carcinomas (SCCs), however, are immortal, a phenotype that is associated with p53 and INK4A dysfunction, high levels of telomerase and loss of heterozygosity (LOH) at several genetic loci, suggestive of the dysfunction of other mortality genes. We show here that human chromosome 6 specifically reduces the proliferation or viability of a human SCC line, BICR31, possessing LOH across the chromosome. This was determined by an 88% reduction in colony yield (P<0.001), following the reintroduction of an intact normal chromosome 6 by monochromosome transfer. Deletion analysis of immortal segregants using polymorphic markers revealed the loss of a 2.9 Mbp interval, centred on marker D6S1045 at 6q14.3-q15, in 6/19 segregants. Crucially, allelic losses of this region were not identified in control hybrids constructed between chromosome 6 and the BICR6 SCC cell line that is heterozygous for chromosome 6 and which showed no reduction in colony formation relative to the control chromosome transfers. This indicates that the minimally deleted region at D6S1045 is not the result of fragile sites, a recombination hot spot, or a feature of the monochromosome transfer technique. LOH of D6S1045 was found in 2/9 immortal SCC lines and was part of a minimally deleted region of line BICR19. Furthermore, allelic imbalance, consistent with LOH, was detected in 3/17 advanced SCCs of the tongue. These results suggest the existence of a suppressor of SCC immortality and tumour development at chromosome 6q14.3-q15, which is important to a subset of human SCCs.

Detailed gene expression analysis but not microsatellite marker analysis of 9p21 reveals differential defects in the INK4a gene locus in the majority of head and neck cancers

The INK4a gene locus on chromosome 9p21 encodes two proteins, p16(INK4a) and p14(ARF), which influence cell cycle control regulated by pRb and p53. The objective of this study was to use different methods for the analysis of the incidence of changes at the INK4a locus in head and neck cancer (HNSCC). Primary tumours were analysed for allelic imbalances (AI) with microsatellite markers for chromosome 9, by immunohistochemistry (IHC) and IHC with enhanced sensitivity by tyramide signal amplification (TSA-IHC), and by RT-PCR. No homozygous deletions at 9p21 were detected. AI at 9p21, which was found in approximately 60% of the tumours, completely failed to indicate the functional inactivation of the two INK4a gene products. Immunostaining of normal squamous epithelia revealed very low levels of p16(INK4a), whereas p14(ARF) was readily detectable. In 160 tumours, IHC suggested a loss of p16(INK4a) expression in 90%. However, by TSA-IHC, only 53.7% showed loss of p16(INK4a) expression, and this was consistent with the RT-PCR analyses. In 100 tumours analysed for both proteins, selective loss of p16(INK4a) occurred in 37%; loss of p14(ARF) was found in only 15%, and selective loss in only 4%; 11% of the tumours had lost both proteins. We conclude that only IHC with high sensitivity and the combined expression analysis of mRNAs and proteins is suitable for studying the role of INK4a in HNSCC. The INK4a gene expression defects are frequent but not universal and primarily affect p16(INK4a). Their clinical impact is still not clear.

A review of inherited cancer syndromes and their relevance to oral squamous cell carcinoma

This paper examines the genetic defects associated with inherited cancer syndromes and their relevance to oral cancer. Tumour suppressor genes are now thought of as either gatekeepers or caretakers according to whether they control cell growth directly by inhibiting cell proliferation and/or promoting cell death (gatekeepers) or whether they maintain the integrity of the genome by DNA repair mechanisms (caretakers). In disorders such as xeroderma pigmentosum, ataxia telangiectasia, Bloom syndrome and Fanconi's anaemia, where there are defective caretaker genes, there is an increased incidence of second primary malignancies, including oral cancer. By contrast, with the exception of Li Fraumeni syndrome, abnormalities of gatekeeper genes do not predispose to oral cancer. Not only do Li Fraumeni patients develop second primary malignancies, but defects of the p53 pathway (p53 mutation, MDM2 over-expression, CDKN2A deletion) appear to be a ubiquitous feature of sporadic oral cancer as it occurs in the West. The findings suggest that genetic instability is of fundamental importance in the pathogenesis of oral cancer.

Carcinogenesis of head and neck cancer and the role of chemoprevention in its reversal

Head and neck cancer is an important public health problem worldwide, accounting for approximately 40,400 new cancer cases and 12,300 cancer deaths annually in the US. Although early-stage disease is often curable with surgery or radiotherapy, the majority of patients present with advanced disease in which despite advances in combined modality therapy the outcomes have not dramatically improved. Furthermore, patients cured of their initial early-stage head and neck squamous cell carcinoma are at high risk for development of second primary tumors, which pose the main threat to survival. An alternative approach in reducing the incidence and thus mortality associated with these cancers is chemoprevention, the use of agents to reverse, halt, or delay carcinogenesis. The carcinogenesis process in head and neck cancer results from a dysregulation of cellular proliferation, differentiation, and cell death resulting from field-wide exposure of the upper aerodigestive tract to tobacco smoking. Newly acquired knowledge in the field of tumor biology and of the genetic changes underlying carcinogenesis through the use of new molecular technology represents the basis on which chemoprevention efforts should be based.

Fine-structure deletion mapping of 10q22-24 identifies regions of loss of heterozygosity and suggests that sporadic follicular thyroid adenomas and follicular thyroid carcinomas develop along distinct neoplastic pathways

Previous studies have demonstrated frequent loss of heterozygosity (LOH) of markers on chromosome arm 10q in both follicular thyroid carcinomas (FTCs) and follicular thyroid adenomas (FAs). A novel tumor suppressor gene, PTEN, has been mapped to 10q23.3 and is the susceptibility gene for Cowden syndrome, an autosomal dominant disorder characterized by multiple hamartomas and a risk of benign and malignant tumors of the breast and thyroid. Studies examining the relationship of somatic PTEN status and follicular thyroid neoplasms have only demonstrated a variable subset of tumors that have somatic monoallelic deletions of PTEN, suggesting that other tumor suppressor genes may be present in this region. We therefore sought to conduct a detailed examination of LOH of 20 polymorphic markers in a 19-cM region spanning 10q22-24, including PTEN, in 44 FAs and 17 FTCs. Using this fine-structure somatic mapping approach, we defined at least two novel regions of LOH in follicular adenomas and follicular carcinomas, suggesting the presence of at least two distinct tumor suppressor genes that may play a role in thyroid neoplasia. Furthermore, the difference in patterns of LOH in adenomas versus carcinomas lends additional support to the hypothesis that adenomas and carcinomas can develop along two separate, nonserial pathways. Genes Chromosomes Cancer 26:322-328, 1999.

Fractional allele loss indicates distinct genetic populations in the development of squamous cell carcinoma of the head and neck (SCCHN)

Loss of heterozygosity (LOH) had been widely used to assess genetic instability in tumours and a high LOH on chromosome arms 3p, 9p and 17p has been considered to be a common event in squamous cell carcinoma of the head and neck (SCCHN). We have investigated LOH in 52 SCCHN using a range of microsatellite markers. LOH was observed in 69% of individuals on 17p using seven markers, in 64% of individuals on 3p using 17 markers and in 61% of individuals on 9p using 11 markers. Fractional allele loss (FAL) has been calculated for each tumour (FAL is the number of chromosomal arms showing LOH divided by the number of informative chromosomal arms) and a median FAL value of 0.25 was obtained in the 52 SCCHN studied. The LOH data were examined on the basis of FAL scores: low FAL (LFAL), 0.00-0.19; medium FAL (MFAL), 0.20-0.32; high FAL (HFAL), 0.33-0.88. HFAL tumours demonstrated a significantly higher LOH on chromosome arms 3p, 9p and 17p, with 94% LOH on 3p, 94% on 9p and 100% on 17p compared with LFAL tumours. Six of the 16 patients in the LFAL group were found to have no LOH on 3p, 9p or 17p and of these four had LOH at other sites, on chromosomes 2p25-p24, 5q21-22, 7pter-p22, 8q13-q22.1, 11q23.3, 13q32, 17q, 18p11.21, 18q21.31 and 19q12-q13.1. These results indicate that LFAL patients form a subset of SCCHN tumours with distinct molecular initiating events which may represent a discrete genetic population.