The DLC-1 -29A/T polymorphism is not associated with nasopharyngeal carcinoma risk in Chinese population

Association of p53 codon72 Arg>Pro polymorphism with susceptibility to nasopharyngeal carcinoma: evidence from a case-control study and meta-analysis

Tumor suppressor p53 is a critical player in the fight against cancer as it controls the cell cycle check point, apoptotic pathways and genomic stability. It is known to be the most frequently mutated gene in a wide variety of human cancers. Single-nucleotide polymorphism of p53 at codon72 leading to substitution of proline (Pro) in place of arginine (Arg) has been identified as a risk factor for development of many cancers, including nasopharyngeal carcinoma (NPC). However, the association of this polymorphism with NPC across the published literature has shown conflicting results. We aimed to conduct a case–control study for a possible relation of p53 codon72 Arg>Pro polymorphism with NPC risk in underdeveloped states of India, combine the result with previously available records from different databases and perform a meta-analysis to draw a more definitive conclusion. A total of 70 NPC patients and 70 healthy controls were enrolled from different hospitals of north-eastern India. The p53 codon72 Arg>Pro polymorphism was typed by polymerase chain reaction, which showed an association with NPC risk. In the meta-analysis consisting of 1842 cases and 2330 controls, it was found that individuals carrying the Pro allele and the ProPro genotype were at a significantly higher risk for NPC as compared with those with the Arg allele and the ArgArg genotype, respectively. Individuals with a ProPro genotype and a combined Pro genotype (ProPro+ArgPro) also showed a significantly higher risk for NPC over a wild homozygote ArgArg genotype. Additionally, the strength of each study was tested by power analysis and genotype distribution by Hardy–Weinberg equilibrium. The outcome of the study indicated that both allele frequency and genotype distribution of p53 codon72 Arg>Pro polymorphism were significantly associated with NPC risk. Stratified analyses based on ethnicity and source of samples supported the above result.

The role of XRCC6/Ku70 in nasopharyngeal carcinoma

The association between XRCC6/Ku70, an upstream player in the DNA double-strand break repair system, and the risk of nasopharyngeal carcinoma (NPC) was examined. In this case-control study, 176 NPC patients and 352 cancer-free controls were genotyped, and the associations of XRCC6 promoter T-991C (rs5751129), promoter G-57C (rs2267437), promoter G-31A (rs132770), and intron 3 (rs132774) polymorphisms with NPC risk were evaluated. NPC tissue samples were also assessed for their XRCC6 mRNA and protein expression by real-time quantitative reverse transcription PCR and Western blotting, respectively. With regard to the XRCC6 promoter T-991C, the TC and CC genotypes were associated with a significantly increased risk of NPC compared with wild-type TT genotype (adjusted odds ratio 2.02 and 3.42, 95% confidence interval 1.21-3.32 and 1.28-8.94, P=0.0072 and 0.0165, respectively). The mRNA and protein expression levels for NPC tissues revealed significantly lower XRCC6 mRNA and protein expression in the NPC samples with TC/CC genotypes compared to those with the TT genotype (P=0.0210 and 0.0164, respectively). These findings suggest that XRCC6 may play an important role in the carcinogenesis of NPC and could serve as a chemotherapeutic target for personalized medicine and therapy.

Promoter methylation of the DLC‑1 gene and its inhibitory effect on human colon cancer

Deleted in liver cancer‑1 (DLC‑1), a candidate tumor suppressor gene which is inactive in liver carcinogenesis, is located at 8p21.3, where deletions are frequently found in several types of human cancer. Promoter hypermethylation is an epigenetic mechanism leading to silencing of the gene expression, which may be the primary cause for the absence of DLC‑1. We investigated the expression of the DLC‑1 gene and the methylation of the DLC‑1 gene in colon cancer cell lines (Caco‑2, LoVo and HT‑29). The data showed that reduced or undetectable levels of DLC‑1 mRNA were found in HT‑29 by reverse transcription-polymerase chain reaction (RT‑PCR). By contrast, the DLC‑1 gene was significantly expressed in Caco‑2 and LoVo cells. These findings were in agreement with the data obtained from western blot analysis. To further determine whether aberrant methylation is a contributing factor to transcriptional inactivation of DLC‑1 in HT‑29, the methylation of promoter was examined using methylation‑specific PCR and sodium bisulfite genomic sequencing in LoVo and HT‑29 cells, which suggests that promoter hypermethylation accounts for silencing of the DLC‑1 gene in HT‑29 cells. Since DLC‑1 is a candidate tumor suppressor gene, we sought to determine whether DLC‑1 expression is associated with cell proliferation in colon cancer cell lines. RNA interference techniques were adopted to inhibit DLC‑1 expression in the LoVo cell line and resulted in inhibition of cell growth and reduced colony formation. Collectively, our observations suggest that hypermethylation is responsible for abrogating the function of the DLC‑1 gene in colon cancer and indicate a role of DLC‑1 in colon carcinogenesis.

Genetic predisposition factors and nasopharyngeal carcinoma risk: a review of epidemiological association studies, 2000-2011: Rosetta Stone for NPC: genetics, viral infection, and other environmental factors

While infection with Epstein-Barr virus (EBV) is known to be an essential risk factor for the development of nasopharyngeal carcinoma (NPC), other co-factors including genetic factors are thought to play an important role. In this review, we summarize association studies conducted over the past decade to evaluate the role of genetic polymorphisms in NPC development. A review of the literature identified close to 100 studies, including 3 genome-wide association studies (GWAS), since 2000 that evaluated genetic polymorphisms and NPC risk in at least 100 NPC cases and 100 controls. Consistent evidence for associations were reported for a handful of genes, including immune-related HLA Class I genes, DNA repair gene RAD51L1, cell cycle control genes MDM2 and TP53, and cell adhesion/migration gene MMP2. However, for most of the genes evaluated, there was no effort to replicate findings and studies were largely modest in size, typically consisting of no more than a few hundred cases and controls. The small size of most studies, and the lack of attempts at replication have limited progress in understanding the genetics of NPC. Moving forward, if we are to advance our understanding of genetic factors involved in the development of NPC, and of the impact of gene-gene and gene-environment interations in the development of this disease, consortial efforts that pool across multiple, well-designed and coordinated efforts will most likely be required.

Loss of DLC1 is an independent prognostic factor in patients with oral squamous cell carcinoma

Deleted in liver cancer (DLC1), a Rho GTPase-activating protein, was observed to be differentially expressed in oral squamous cell carcinoma in comparison with normal tissues using tissue proteomics. In the current study, we investigated the clinical significance of loss of DLC1 expression in different stages of development of oral squamous cell carcinoma to determine its potential as a biomarker for oral dysplasia and prognosis of oral squamous cell carcinoma. Immunohistochemical analysis of DLC1 expression was carried out in oral squamous cell carcinoma patients (n=214), dysplasia (n=51), hyperplastic squamous mucosa (n=45), and histologically normal oral tissues (n=80), and correlated with clinicopathological parameters and disease prognosis over 91 months for oral squamous cell carcinomas. Loss of DLC1 expression was observed in oral squamous cell carcinoma (64%), oral dysplasia (31%), hyperplastic squamous mucosa (22%), and normal mucosa (16%). Significant loss of DLC1 expression was observed in oral squamous cell carcinomas as compared with dysplasia (P<0.001, odds ratio=3.8, 95% CI=2.0-7.3), suggesting it may be an important event involved in cancer progression. Among oral squamous cell carcinomas, the loss of DLC1 expression was significantly associated with poor prognosis (P=0.021, hazards ratio (HR)=1.8, 95% CI=1.1-2.9). Multivariate analysis revealed loss of DLC1 (P=0.023, HR=2.1, 95% CI=1.2-3.9) and histopathological grade (P=0.015, HR=1.7, 95% CI=1.1-2.7) to be independent predictors for disease-free survival in oral squamous cell carcinoma patients in comparison with known prognostic factors, viz. tumor stage, nodal status, and overall stage. Loss of DLC1 expression emerged as an important biomarker for predicting patients diagnosed with oral dysplasia at high risk of transformation upon future validation in longitudinal studies. Loss of DLC1 expression is a poor prognostic marker for oral squamous cell carcinoma patients.

Polymorphism of VEGF-2578C/A associated with the risk and aggressiveness of nasopharyngeal carcinoma in a Chinese population

Polymorphism of vascular endothelial growth factor (VEGF) influences the VEGF responsiveness and is implicated in various types of diseases with a putative angiogenic basis, but its role in nasopharyngeal carcinoma (NPC) is not fully understood. In this report, we sought to investigate whether the VEGF-2578C/A polymorphism was associated with NPC in a Chinese population. We carried out polymerase chain reaction-restriction fragment length polymorphism in blood genomic DNA of 156 NPC patients and 161 control subjects. The VEGF-2578A allele carriers were significantly associated with an increased risk of NPC (odds ratio: 1.648; 95% confidence interval: 1.053-2.580; P = 0.029). In contrast, NPC patients with the -2578CC genotype were shown higher tumor aggressiveness of large tumor size, poor differentiation and advanced stage as compared to the -2578A allele carriers. No correlation was observed between the genotype or allele distribution and lymph node metastasis or family history of cancer. The VEGF-2578C/A polymorphism was shown to be inconsistent with the onset and aggressiveness of NPC. The precise mechanisms of the polymorphism on the differing status in NPC should be elucidated in further studies.