Background: Lung cancer is the most prevalent malignancy in adults. Circular RNA (circRNA) circCPA4 (hsa_circ_0082374) is highly expressed in non-small cell lung cancer (NSCLC). The purpose of this study was to explore the role and mechanism of circCPA4 in lung cancer. Methods: CircCPA4, linear CPA4, TGF-β-induced factor homeobox 2 (TGIF2), and microRNA-214-3p (miR-214-3p) levels were measured by real-time quantitative polymerase chain reaction (RT-qPCR). The protein levels of TGIF2, Beclin1, and p62 were assessed by western blot assay. Colony numbers, migration, invasion, apoptosis, and cell cycle progression were examined by colony formation, wound-healing, transwell, and flow cytometry assays, respectively. The binding relationship between miR-214-3p and circCPA4 or TGIF2 was predicted by StarBase or TargetScan and then verified by a dual-luciferase reporter, RNA immunoprecipitation (RIP), and RNA pulldown assays. The biological role of circCPA4 on lung tumor growth was assessed by a xenograft tumor model in vivo, and TGIF2 and ki-67 expression was assessed by immunohistochemistry. Results: We determined that CircCPA4 and TGIF2 were increased, and miR-214-3p was decreased in lung cancer tissues and cells. Functionally, circCPA4 knockdown could suppress colony formation, migration, invasion, cell cycle progression, and expedite apoptosis of lung cancer cells in vitro. Mechanically, circCPA4 could regulate TGIF2 expression by sponging miR-214-3p. In addition, circCPA4 deficiency inhibited the tumor growth in lung cancer in the mouse model. Conclusions: CircCPA4 could act as a sponge of miR-214-3p to upregulate TGIF2 expression, thereby promoting the progression of lung cancer cells. These findings suggested underlying therapeutic targets for the treatment of lung cancer.

Lung cancer is the leading cause of cancer-related deaths in both men and women worldwide. The influence of environment-gene interactions on lung carcinogenesis has been well demonstrated by phase I and II enzymes that are involved in the metabolic activation and detoxification of carcinogens. Carcinogens are oxidized by phase I enzymes such as cytochrome P450 into reactive metabolites that are then detoxified by phase II enzymes. Cytochrome P450 is a large family of genes and has 72 different members with a large number of polymorphic forms [1] . The cytochrome P450 1A1 (CYP1A1) gene is important for the activation of precarcinogens [2] . The CYP1A1 gene is involved in the activation step in the metabolism of polycyclic aromatic hydrocarbons (PAHs) found in tobacco smoke, converting them to carcinogens and is expressed in human lung cells [3] . The CYP1A1 gene has several polymorphic forms [4] . The m1 polymorphism in the 3' non-coding region (3'-UTR) of the CYP1A1 gene arises from a T→C transition, thus the m1 allele bears a MspI cleavage site, in contrast with the wild-type variant [5] . The CYP1A1 m1 polymorphic allele affects the transcriptional control elements involved in enzyme inducibility [6] . The variant genotype has a high prevalence among Asians [7] compared to Caucasians [8] and African Americans [9] . The p16 gene [10] , which is a tumor suppressor gene, is frequently altered in lung cancers. Methylation of the 5'CpG island in the promoter of the p16 seems to be the major mechanism through which p16 become inactivated [11] . A case control study was conducted among 47 cases of lung cancer and 94 controls who came from China. The genetic polymorphism of CYP1A1 was tested with method of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to investigate the relationship between the genetic polymorphism of CYP1A1 and the genetic susceptibility to lung cancer, and a methylation-specific PCR (MSP) was performed to detect p16 methylation in order to study the effects of the methylation in p16 gene on the risk of lung cancer in China. Materials and methods Study subjectsIn this study one hundred and forty-one subjects who came from Anhui of China were enrolled. Written consent was obtained from each of them. Among them, 47Abstract Objective: To investigate the relationship between the genetic polymorphism of CYP1A1 and the genetic susceptibility to lung cancer as well as to study the effects of the methylation in p16 gene on the risk of lung cancer in a Chinese population. Methods: A case control study was conducted among 47 cases of lung cancer and 94 controls. The genetic polymorphism of CYP1A1 was tested with method of PCR-RFLP, and a methylation-specific PCR (MSP) was performed to detect p16 methylation. Results: It showed that there was no significant difference in frequencies of the genotypes of CYP1A1 between the two groups (P > 0.05). Synergistic effects were not found between smoking and CYP1A1. Methylated p16 gene was found in 44.7% (21/47) of lung cancer tis...