Chek2 And Susceptibility To Lung Cancer Associated With The Mechanism Rev3l Gene Polymorphism

Lung cancer is the leading cause of cancer-related deaths worldwide and tobacco smoking is one of the most important causes of lung cancer. Since the accumulation of mutations and chromosomal aberrations are the hallmarks of cancer cells, it has been hypothesized that cancer susceptibility derives from hypomorphic variants of DNA repair and checkpoint control genes. The loss of genome-maintenance mechanisms such as DNA repair and cell cycle checkpoint control may result in chromosomal abnormalities.Checkpoint kinase 2 (CHEK2), a tumor-suppressor gene, plays an essential role in the DNA damage checkpoint response cascade. The list of CHEK2 mutations in cancer cells is continuously expanding and the CHEK2 gene has been postulated as a susceptibility gene for a number of other common cancers, including prostate, colorectal cancers and hematopoietic neoplasms. In recent years, CHEK2 mutations have been found in lung cance. Since CHEK2 expression is ubiquitous in mammalian cells, individual differences in lung cancer susceptibility may be determined to be the consequence of impaired CHEK2 expression. We therefore hypothesized that polymorphisms in the CHEK2 gene promoter may modify its transcription and create a susceptibility to lung cancer.We first investigated two polymorphisms in the proximal promoter of the CHEK2 gene and evaluated its association with the risk of lung cancer in a case-control study using 500 incident lung cancer cases and 517 cancer-free controls. We found that CHEK2 rs2236141-48 G>A was significantly associated with lung cancer risk (P= 0.0018). Similar results were obtained in a follow-up replication study in 575 lung cancer patients and 589 controls (P= 0.042). Quantitative PCR showed that individuals with the G allele had lower levels of CHEK2 transcripts in peripheral blood mononuclear cells and normal lung tissues. The-48 G→A variant eliminated a methylation site and thereby relieve the transcriptional repression of CHEK2. Therefore, this polymorphism affected downstream transcription through genetic and epigenetic modifications. Luciferase reporter assays demonstrated that the major G allele significantly attenuated reporter gene expression when methylated. Electro-mobility shift assays (EMSA) and surface plasmon resonance (SPR) revealed that the methylated G allele increased transcription factor accessibility. We used in vivo chromatin immunoprecipitation (ChIP) to confirm that the relevant transcription factor was Spl. Using lung tissue heterozygous for the G/A SNP, we found that Spl acted as a repressor and had a stronger binding affinity for the G allele. These results support our hypothesis that the CHEK2 rs2236141 variant modifies lung cancer susceptibility in the Chinese population by affecting CHEK2 expression. Lung cancer remains the leading cause of cancer-related deaths worldwide. The environment, especially tobacco smoke has proved to be the most important trigger of lung cancer. However, only a fraction of smokers develop lung cancer, suggesting synergy of genetic susceptibility with environment.Cells constantly encounter various carcinogens or cytoxic agents. These compounds directly or indirectly provoke DNA damage creating mutations, DNA cross-links or DNA strand breaks, which lead to DNA instability. Eukaryotic cells from yeast to human possess DNA post-replication repair (PPR) or DNA damage tolerance system. Translesion DNA synthesis (TLS) and homologous DNA recombination (HR) are two major postreplicational repair pathways. The ubiquitous translesion DNA synthesis consists of a series of specialized polymerases, including polymeraseκ,ζ,ηandι.REV3Lp, the catalytic subunit of DNA polymerase zeta is the major participant in translesion DNA synthesis (TLS). Recent evidence suggests that REV3L plays an important role in the maintenance of genome stability despite its mutagenic characteristics. Such function makes it a genetic susceptibility gene for cancers. Here, we investigated 15 common polymorphisms in the REV3L gene in a case-control study of 500 incident lung cancer patients and 517 cancer-free controls in a Chinese population. Single locus analysis revealed that three SNPs (rs465646, rs459809 and rs1002481) were significantly associated with the risk for lung cancer. One of the strongest associations comes from the 3'UTR 460 T>C polymorphism (rs465646). The C-allele was significantly associated with reduced lung cancer risk (P= 0.015). Similar results were obtained in a follow-up replication study in another 575 lung cancer cases and 589 controls (P= 0.049). This 3'UTR 460 T>C variation was predicted to modulate the binding of several micorRNAs. We found that the T-allele demonstrated stronger binding affinity for miR-25 and miR-32, which was accompanied by significantly weaker reporter expression level. Cigarette smoke extracts could upregulate and downregulate the expression of REV3L and miR-32, respectively. Overexpression of REV3L attenuated foci and micronucleus formation, indicating the tumor-suppressing role of REV3L. Our data also shows a significant reduction of REV3L gene expression in 46 lung carcinomas when compared to normal adjacent tissues. These results support our hypothesis that the REV3L rs465646 variant modifies lung cancer susceptibility in the Chinese population by affecting microRNA-mediated regulation.Extending our previous association study, we have successfully identified the risk contributing polymorphism in the REV3L gene and a possible underlying mechanism in carcinogenesis.