BPDE-induced lymphocytic 3p21.3 aberrations may predict head and neck carcinoma risk

Screening of candidate tumor-suppressor genes in 3p21.3 and investigation of the methylation of gene promoters in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is the most common type of head and neck malignant tumor. however, its pathological mechanisms have not yet been elucidated. In the present study, we screened for candidate tumor-suppressor genes (TSGs) related to OSCC among 10 candidate genes located in 3p21.3, a region abundant with TSGs based on previous studies, using semi-quantitative reverse transcription PCR (RT-PCR). Three genes, GNAT1, SEMA3B and AXUD1, with low or no expression in OSCC tissues and the cell line TCA8113 were selected, and the promoter methylation status was further analyzed by methylation-specific PCR (MS-PCR). Hypermethylation in the promoter regions of SEMA3B was found in OSCC tissues, and a significant difference in the frequency of methylation of SEMA3B was observed between OSCC and non-cancerous tissues. Furthermore, TCA8113 cells treated with 5-Aza-Cdc started to re-express SEMA3B at a concentration of 5 µM or higher. Our study confirmed that three candidate TSGs with low expression may be involved in OSCC and that hypermethylation in promoter regions may contribute to the low expression of SEMA3B. These findings offer novel insights for clarifying the molecular mechanisms of tumorigenesis of OSCC as well as for aiding in its clinical diagnosis and therapeutic strategy.

Association of inter- and intrachromosomal exchanges with the distribution of low- and high-LET radiation-induced breaks in chromosomes

To study the effects of low- and high-linear energy transfer (LET) radiation on break locations within a chromosome, we exposed human epithelial cells in vitro to (137)Cs γ rays at both low and high dose rates, secondary neutrons at a low dose rate, and 600 MeV/u iron ions at a high dose rate. Breakpoints were identified using multicolor banding in situ hybridization (mBAND), which paints chromosome 3 in 23 different colored bands. For all four radiation scenarios, breakpoint distributions were found to be different from the predicted distribution based on band width. Detailed analysis of chromosome fragment ends involved in inter- or intrachromosomal exchanges revealed that the distributions of fragment ends participating in interchromosomal exchanges were similar between the two low-LET radiation dose rates and between the two high-LET radiation types, but the distributions were less similar between low- and high-LET radiations. For fragment ends participating in intrachromosomal exchanges, the distributions for all four radiation scenarios were similar, with clusters of breaks found in three regions. Analysis of the locations of the two fragment ends in chromosome 3 that joined to form an intrachromosomal exchange demonstrated that two breaks with a greater genomic separation can be more likely to rejoin than two closer breaks, indicating that chromatin folding can play an important role in the rejoining of chromosome breaks. Comparison of the breakpoint distributions to the distributions of genes indicated that the gene-rich regions do not necessarily contain more breaks. In general, breakpoint distributions depend on whether a chromosome fragment joins with another fragment in the same chromosome or with a fragment from a different chromosome.

BPDE induced lymphocytic chromosome 3p deletions may predict renal cell carcinoma risk

PURPOSE

Cigarette smoking is a risk factor for renal cell carcinoma. BPDE (benzo[alpha]pyrene diol epoxide) (Midwest Research Institute, Kansas City, Missouri), which is a major constituent of cigarette smoke, induces 3p aberrations that are associated with susceptibility to other smoking associated cancers. Because chromosome 3p deletions are known to be the most frequent genetic alterations in renal cell carcinoma, we tested whether 3p sensitivity to BPDE predicts susceptibility to renal cell carcinoma.

MATERIALS AND METHODS

Cultured peripheral blood lymphocytic cells from 170 cases and 135 controls were treated with 2 microM BPDE for 24 hours and assessed for 3p deletions by fluorescence in situ hybridization using probes directed to 3p25.2, 3p21.3, 3p14.2 and 3p12.2. A probe for 3q13 served as a control. One thousand lymphocyte interphases were scored per sample.

RESULTS

At each locus BPDE induced 3p deletions were significantly more common in cases than in controls. No significant differences between cases and controls were observed for deletions in 3q13. Using the median value in controls as the cutoff point for BPDE sensitivity we found that the OR in subjects with high BPDE sensitivity at 3p25.2, 3p21.3, 3p14.2 and 3p12.2 was 2.02 (95% CI 1.18-3.46), 2.28 (95% CI 1.33-3.92), 1.84 (95% CI 1.07-3.16) and 1.97 (95% CI 1.15-3.37), respectively. There were dose dependent relationships between the number of deletions at each locus and the risk of renal cell carcinoma.

CONCLUSIONS

This study demonstrates that chromosome 3p may be a specific molecular target of cigarette carcinogens and BPDE sensitivity in chromosome 3p may reflect the genetic susceptibility of an individual to renal cell carcinoma.

Chromosomal radiosensitivity in head and neck cancer patients: evidence for genetic predisposition?

The association between chromosomal radiosensitivity and genetic predisposition to head and neck cancer was investigated in this study. In all, 101 head and neck cancer patients and 75 healthy control individuals were included in the study. The G(2) assay was used to measure chromosomal radiosensitivity. The results demonstrated that head and neck cancer patients had a statistically higher number of radiation-induced chromatid breaks than controls, with mean values of 1.23 and 1.10 breaks per cell, respectively (P<0.001). Using the 90th percentile of the G(2) scores of the healthy individuals as a cutoff value for chromosomal radiosensitivity, 26% of the cancer patients were radiosensitive compared with 9% of the healthy controls (P=0.008). The mean number of radiation-induced chromatid breaks and the proportion of radiosensitive individuals were highest for oral cavity cancer patients (1.26 breaks per cell, 38%) and pharynx cancer patients (1.27 breaks per cell, 35%). The difference between patients and controls was most pronounced in the lower age group (<or=50 years, 1.32 breaks per cell, 38%) and in the non- and light smoking patient group (<or=10 pack-years, 1.28 breaks per cell, 46%). In conclusion, enhanced chromosomal radiosensitivity is a marker of genetic predisposition to head and neck cancer, and the genetic contribution is highest for oral cavity and pharynx cancer patients and for early onset and non- and light smoking patients.

Fluorescence in situ hybridization is necessary to detect an association between chromosome aberrations and polycyclic aromatic hydrocarbon exposure in utero and reveals nonrandom chromosome involvement

Chromosome aberrations are associated with environmental exposures in infants and children. Recently we reported that prenatal exposure to airborne polycyclic aromatic hydrocarbons (PAHs) was significantly (P < 0.01) associated with stable aberration frequencies in cord blood from a subset of 60 newborns from the Columbia Center for Children's Environmental Health Prospective Cohort Study (Bocskay K et al. [ 2005]: Cancer Epidemiol Biomarkers Prev 14:506-511). To determine whether the environmental exposures may be targeting specific chromosomes and to compare various methods for measuring chromosome aberrations, we further evaluated this same subset of subjects composed of African-American and Dominican nonsmoking mother-newborn pairs residing in low-income neighborhoods of New York City, and exposed to varying levels of airborne PAHs. Chromosome aberrations were measured in cord blood lymphocytes, both by whole chromosome probe (WCP) fluorescence in situ hybridization (FISH) and traditional Giemsa-staining. Prenatal exposures were assessed by personal air monitoring. Breaks in chromosomes 1-6, as detected by WCP FISH, were nonrandomly distributed, underscoring the importance of appropriate chromosome probe selection to capture cytogenetic damage in response to exposure. FISH for stable aberrations was found to be a more sensitive method for detecting aberration frequencies associated with environmental exposures, when compared with FISH for unstable aberrations or Giemsa-staining for aberrations. Together, these results suggest that PAHs may be targeting specific chromosomes and highlight the importance of using the more sensitive detection methods to assess risk in populations with low levels of exposure.

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.

Perspectives on the molecular epidemiology of aerodigestive tract cancers

Improving laboratory techniques and the greater availability of genetic data have led to a flurry of publications from molecular epidemiologic studies on aerodigestive tract cancers. Inconsistent results have been observed in studies of sequence variants, due to limitations such as small sample size, possible detection of false positives, moderate prior probabilities that each SNP confers a substantial increase in cancer risk, and publication bias. Meta- and pooled-analyses were shown to be effective in elucidating modest increases in aerodigestive tract cancer risk attributable to sequence variants. Phenotypic assays developed to quantify an individual's DNA repair capacity have been applied to epidemiological studies on aerodigestive tract cancers. Epigenetic events have also been studied in tumor progression and as susceptibility factors for aerodigestive tract cancers, in smaller scale studies. It is imperative that limitations of previous studies are addressed for future research in the molecular epidemiology of aerodigestive tract cancers. Some recommendations for future research are to: (i) incorporate multiple markers of different types (ex. genotype and phenotype data), (ii) enhance statistical power by conducting studies with larger sample size, and developing consortia to coordinate research efforts, (iii) improve marker selection via a hybrid strategy of incorporating data on evolutionary biology and physico-chemical properties of amino acids, with haplotype/tag SNP data, (iv) employ novel statistical methods such as hierarchical modeling with Bayesian adjustments, false positive reporting probability and modeling of complex pathways. Consortia have been initiated for head and neck cancer (International Head and Neck Cancer Epidemiology Consortium (INHANCE)) and lung cancer (International Lung Cancer Consortium (ILCCO)) with the aim to share comparable data, to focus on rare subgroups such as nonsmokers and to coordinate laboratory analyses. Such collaborative efforts and integration across disciplines will be essential in contributing to the elucidation of genetic susceptibility to aerodigestive tract cancers.