The role of XRCC6/Ku70 in nasopharyngeal carcinoma

Non-Homologous End-Joining Pathway Genotypes Significantly Associated with Nasopharyngeal Carcinoma Susceptibility

Defects in the non-homologous end-joining (NHEJ) DNA repair pathway lead to genomic instability and carcinogenesis. However, the roles of individual NHEJ genes in nasopharyngeal carcinoma (NPC) etiology are not well-understood. The aim of this study was to assess the contribution of NHEJ genotypes, including XRCC4 (rs6869366, rs3734091, rs28360071, rs28360317, rs1805377), XRCC5 (rs828907, rs11685387, rs9288518), XRCC6 (rs5751129, rs2267437, rs132770, rs132774), XRCC7 rs7003908, and Ligase4 rs1805388, to NPC risk, with 208 NPC patients and 416 controls. Genotype-phenotype correlations were also investigated by measuring mRNA and protein expression in adjacent normal tissues and assessing the NHEJ repair capacity in blood lymphocytes from 43 NPC patients. The results showed significant differences in the distributions of variant genotypes at XRCC4 rs3734091, rs28360071, and XRCC6 rs2267437 between the cases and controls. The variant genotypes of these three polymorphisms were associated with significantly increased NPC risks. NPC patients with the risk genotypes at XRCC6 rs2267437 had significantly reduced expression levels of both mRNA and protein, as well as a lower NHEJ repair capacity, than those with the wild-type genotype. In conclusion, XRCC4 rs3734091, rs28360071, and XRCC6 rs2267437 in the NHEJ pathway were associated with NPC susceptibility. XRCC6 rs2267437 can modulate mRNA and protein expression and the NHEJ repair capacity.

DNA-PK in human malignant disorders: Mechanisms and implications for pharmacological interventions

The DNA-PK holoenzyme is a fundamental element of the DNA damage response machinery (DDR), which is responsible for cellular genomic stability. Consequently, and predictably, over the last decades since its identification and characterization, numerous pre-clinical and clinical studies reported observations correlating aberrant DNA-PK status and activity with cancer onset, progression and responses to therapeutic modalities. Notably, various studies have established in recent years the role of DNA-PK outside the DDR network, corroborating its role as a pleiotropic complex involved in transcriptional programs that operate biologic processes as epithelial to mesenchymal transition (EMT), hypoxia, metabolism, nuclear receptors signaling and inflammatory responses. In particular tumor entities as prostate cancer, immense research efforts assisted mapping and describing the overall signaling networks regulated by DNA-PK that control metastasis and tumor progression. Correspondingly, DNA-PK emerges as an obvious therapeutic target in cancer and data pertaining to various pharmacological approaches have been published, largely in context of combination with DNA-damaging agents (DDAs) that act by inflicting DNA double strand breaks (DSBs). Currently, new generation inhibitors are tested in clinical trials. Several excellent reviews have been published in recent years covering the biology of DNA-PK and its role in cancer. In the current article we are aiming to systematically describe the main findings on DNA-PK signaling in major cancer types, focusing on both preclinical and clinical reports and present a detailed current status of the DNA-PK inhibitors repertoire.

Interleukin-18 promoter genotype is associated with the risk of nasopharyngeal carcinoma in Taiwan

Background

The incidence rate of nasopharyngeal carcinoma (NPC) has been documented to be high in Southeast Asia. Interleukin-18 (IL-18) is a multifunctional cytokine that augments interferon-γ production and acts as an important immunomediator in the development of several types of cancer.

Patients and methods

This case-control study evaluated the role of IL-18 in NPC at the DNA level by genotyping its promoter polymorphisms at positions -656, -607, and -137 in a Taiwanese population. A total of 176 patients with NPC and age- and gender-matched 352 noncancer controls were included in this study.

Results

The CC genotype of the IL-18-607 polymorphism was found to be associated with significantly decreased risks of NPC compared to the AA genotype (crude OR =0.50, 95% CI =0.29-0.84, P=0.0093). This significant difference persisted even in the dominant and recessive models. A significantly lower C allele frequency at position -607 was detected in the NPC group(41.8% vs 50.3%; OR =0.77; 95% CI =0.63-1.04, P=0.0089). Regarding IL-18-656 and -137 polymorphisms, there were no differential distributions of their genotypes between the NPC and control groups. After substratification of the subjects according to their smoking, alcohol consumption, and areca chewing status, the genotype distribution of the IL-18-607 polymorphism was found to be different only among nonsmokers between the NPC and control subgroups.

Conclusion

This study suggests that IL-18 plays an important role in the carcinogenesis of NPC in Taiwan and that the genotype-phenotype correlation of IL-18-607 polymorphism and its contribution to NPC need to be investigated further.

The contribution of interleukin-8 genotypes and expression to nasopharyngeal cancer susceptibility in Taiwan

The incidence rate of nasopharyngeal cancer (nasopharyngeal carcinoma [NPC]) is much higher in Southeast Asia than in western countries. Interleukin-8 (IL-8), a chemokine produced by macrophages, epithelial cells, airway smooth muscle cells, and endothelial cells, is an important immuno-mediator in the development and progression of many types of cancer. Genetic variations in IL-8 have been associated with the risks of NPC and other cancers. In the current study, we evaluated the role of IL-8 in NPC at the levels of DNA, RNA, and protein in a Taiwanese population. First, in a case-control study, 176 NPC patients and 352 cancer-free controls were genotyped, and the associations of IL-8 T - 251A, C + 781T, C + 1633T, and A + 2767T polymorphisms with NPC risk were evaluated. Second, the NPC tissue samples were assessed for their IL-8 mRNA and protein expression by real-time quantitative reverse transcription polymerase chain reaction (PCR) and Western blotting, respectively. Regarding the IL-8 promoter T - 251A, the TA and AA genotypes were associated with significantly decreased risks of NPC compared with the wild-type TT genotype (adjusted odds ratio = 0.61 and 0.52, 95% confidence interval = 0.47-0.93 and 0.37-0.91, P = .0415 and .0289, respectively). The mRNA and protein expression levels for NPC tissues revealed no significant associations among the 20 NPC samples with different genotypes. These findings suggest that IL-8 may play an important role in the carcinogenesis of NPC in Taiwan.

The Role of the Core Non-Homologous End Joining Factors in Carcinogenesis and Cancer

DNA double-strand breaks (DSBs) are deleterious DNA lesions that if left unrepaired or are misrepaired, potentially result in chromosomal aberrations, known drivers of carcinogenesis. Pathways that direct the repair of DSBs are traditionally believed to be guardians of the genome as they protect cells from genomic instability. The prominent DSB repair pathway in human cells is the non-homologous end joining (NHEJ) pathway, which mediates template-independent re-ligation of the broken DNA molecule and is active in all phases of the cell cycle. Its role as a guardian of the genome is supported by the fact that defects in NHEJ lead to increased sensitivity to agents that induce DSBs and an increased frequency of chromosomal aberrations. Conversely, evidence from tumors and tumor cell lines has emerged that NHEJ also promotes chromosomal aberrations and genomic instability, particularly in cells that have a defect in one of the other DSB repair pathways. Collectively, the data present a conundrum: how can a single pathway both suppress and promote carcinogenesis? In this review, we will examine NHEJ's role as both a guardian and a disruptor of the genome and explain how underlying genetic context not only dictates whether NHEJ promotes or suppresses carcinogenesis, but also how it alters the response of tumors to conventional therapeutics.