Dapagliflozin administration to a mouse model of type 2 diabetes induces DNA methylation and gene expression changes in pancreatic islets.

Decreased pancreatic ß-cell volume is a serious problem in patients with type 2 diabetes mellitus, and there is a need to establish appropriate treatments. Increasingly, sodium/glucose cotransporter 2 (SGLT2) inhibitors, which have a protective effect on pancreatic ß-cells, are being prescribed to treat diabetes; however, the underlying mechanism is not well understood. We previously administered SGLT2 inhibitor dapagliflozin to a mouse model of type 2 diabetes and found significant changes in gene expression in the early-treated group, which led us to hypothesize that epigenetic regulation was a possible mechanism of these changes. Therefore, we performed comprehensive DNA methylation analysis by methylated DNA immunoprecipitation using isolated pancreatic islets after dapagliflozin administration to diabetic model mice. As a result, we identified 31 genes with changes in expression due to DNA methylation changes. Upon immunostaining, cystic fibrosis transmembrane conductance regulator and cadherin 24 were found to be upregulated in islets in the dapagliflozin-treated group. These molecules may contribute to the maintenance of islet morphology and insulin secretory capacity, suggesting that SGLT2 inhibitors' protective effect on pancreatic ß-cells is accompanied by DNA methylation changes, and that the effect is long-term and not temporary. In future diabetes care, SGLT2 inhibitors may be expected to have positive therapeutic effects, including pancreatic ß-cell protection.

l-Asparaginase regulates mTORC1 activity via a TSC2-dependent pathway in pancreatic beta cells.

Eif2ak4, a susceptibility gene for type 2 diabetes, encodes GCN2, a molecule activated by amino acid deficiency. Mutations or deletions in GCN2 in pancreatic ß-cells increase mTORC1 activity by decreasing Sestrin2 expression in a TSC2-independent manner. In this study, we searched for molecules downstream of GCN2 that suppress mTORC1 activity in a TSC2-dependent manner. To do so, we used a pull-down assay to identify molecules that competitively inhibit the binding of the T1462 phosphorylation site of TSC2 to 14-3-3. l-asparaginase was identified. Although l-asparaginase is frequently used as an anticancer drug for acute lymphoblastic leukemia, little is known about endogenous l-asparaginase. l-Asparaginase, which is expressed downstream of GCN2, was found to bind 14-3-3 and thereby to inhibit its binding to the T1462 phosphorylation site of TSC2 and contribute to TSC2 activation and mTORC1 inactivation upon TSC2 dephosphorylation. Further investigation of the regulation of mTORC1 activity in pancreatic ß-cells by l-asparaginase should help to elucidate the mechanism of diabetes and insulin secretion failure during anticancer drug use.

Histone deacetylase 6 regulates insulin signaling in pancreatic ß cells.

The reduction of pancreatic ß cell mass is one of the key factors for the onset of type 2 diabetes. Many reports have indicated that insulin signaling is important for type 2 diabetes, but the mechanism by which insulin signaling is altered in pancreatic ß cells remains unclear. This study was designed to examine the role of histone deacetylases (HDACs) in the regulation of insulin signaling in pancreatic ß cells. We found that insulin signaling was downregulated by inhibition of HDAC6. HDAC6 expression was specifically observed in pancreatic ß cells and was decreased in the pancreatic islets of a type 2 diabetes mouse model. When a mouse pancreatic ß cell line (MIN6 cells) was treated with palmitic acid to mimic the effect of a high-fat diet on pancreatic ß cells, HDAC6 was imported into the nucleus. These results suggest that HDAC6 plays an important role in the regulation of insulin signaling in pancreatic ß cells. Therefore, clarifying the regulation of insulin signaling by HDAC6 may be a valuable approach for the treatment of type 2 diabetes.

Casein kinase 2 phosphorylates and stabilizes C/EBPß in pancreatic ß cells.

During the development of type 2 diabetes, endoplasmic reticulum (ER) stress leads to pancreatic ß cell failure. CCAAT/enhancer-binding protein (C/EBP) ß is highly induced by ER stress and AMP-activated protein kinase (AMPK) suppression in pancreatic ß cells, and its accumulation reduces pancreatic ß cell mass. We investigated the phosphorylation state of C/EBPß under these conditions. Casein kinase 2 (CK2) was found to co-localize with C/EBPß in MIN6 cells. It phosphorylated S222 of C/EBPß, a previously unidentified phosphorylation site. We found that C/EBPß is phosphorylated by CK2 under AMPK suppression and ER stress, which are important from the viewpoint of the worsening pathological condition of type 2 diabetes, such as decreased insulin secretion and apoptosis of pancreatic ß cells.

Paternal allelic mutation at the Kcnq1 locus reduces pancreatic ß-cell mass by epigenetic modification of Cdkn1c.

Genetic factors are important determinants of the onset and progression of diabetes mellitus. Numerous susceptibility genes for type 2 diabetes, including potassium voltage-gated channel, KQT-like subfamily Q, member1 (KCNQ1), have been identified in humans by genome-wide analyses and other studies. Experiments with genetically modified mice have also implicated various genes in the pathogenesis of diabetes. However, the possible effects of the parent of origin for diabetes susceptibility alleles on disease onset have remained unclear. Here, we show that a mutation at the Kcnq1 locus reduces pancreatic ß-cell mass in mice by epigenetic modulation only when it is inherited from the father. The noncoding RNA KCNQ1 overlapping transcript1 (Kcnq1ot1) is expressed from the Kcnq1 locus and regulates the expression of neighboring genes on the paternal allele. We found that disruption of Kcnq1 results in reduced Kcnq1ot1 expression as well as the increased expression of cyclin-dependent kinase inhibitor 1C (Cdkn1c), an imprinted gene that encodes a cell cycle inhibitor, only when the mutation is on the paternal allele. Furthermore, histone modification at the Cdkn1c promoter region in pancreatic islets was found to contribute to this phenomenon. Our observations suggest that the Kcnq1 genomic region directly regulates pancreatic ß-cell mass and that genomic imprinting may be a determinant of the onset of diabetes mellitus.

Dietary Mung Bean Protein Reduces Hepatic Steatosis, Fibrosis, and Inflammation in Male Mice with Diet-Induced, Nonalcoholic Fatty Liver Disease.

BACKGROUND: As the prevalence of nonalcoholic fatty liver disease (NAFLD), including steatosis and nonalcoholic steatohepatitis, is increasing, novel dietary approaches are required for the prevention and treatment of NAFLD. OBJECTIVE: We evaluated the potential of mung bean protein isolate (MuPI) to prevent NAFLD progression. METHODS: In Expts. 1 and 2, the hepatic triglyceride (TG) concentration was compared between 8-wk-old male mice fed a high-fat diet (61% of energy from fat) containing casein, MuPI, and soy protein isolate and an MuPI-constituent amino acid mixture as a source of amino acids (18% of energy) for 4 wk. In Expt. 3, hepatic fatty acid synthase (Fasn) expression was evaluated in 8-wk-old male Fasn-promoter-reporter mice fed a casein- or MuPI-containing high-fat diet for 20 wk. In Expt. 4, hepatic fibrosis was examined in 8-wk-old male mice fed an atherogenic diet (61% of energy from fat, containing 1.3 g cholesterol/100 g diet) containing casein or MuPI (18% of energy) as a protein source for 20 wk. RESULTS: In the high fat-diet mice, the hepatic TG concentration in the MuPI group decreased by 66% and 47% in Expt. 1 compared with the casein group (P < 0.001) and the soy protein isolate group (P = 0.001), respectively, and decreased by 56% in Expt. 2 compared with the casein group (P = 0.011). However, there was no difference between the MuPI-constituent amino acid mixture and casein groups in Expt. 2. In Expt. 3, Fasn-promoter-reporter activity and hepatic TG concentration were lower in the MuPI group than in those fed casein (P < 0.05). In Expt. 4, in mice fed an atherogenic diet, hepatic fibrosis was not induced in the MuPI group, whereas it developed overtly in the casein group. CONCLUSION: MuPI potently reduced hepatic lipid accumulation in mice and may be a potential foodstuff to prevent NAFLD onset and progression.

Pathogenesis of selective insulin resistance in isolated hepatocytes.

The development of insulin resistance (IR) in the liver is a key pathophysiologic event in the development of type 2 diabetes. Although insulin loses its ability to suppress glucose production, it largely retains its capacity to drive lipogenesis. This selective IR results in the characteristic hyperglycemia and dyslipidemia of type 2 diabetes. The delineation of two branched pathways of insulin receptor (InsR) signaling to glucose versus triglyceride production, one through FoxO and the other through SREBP-1c, provides a mechanism to account for this pathophysiological abnormality. We tested the complementary hypothesis that selective IR arises due to different intrinsic sensitivities of glucose production versus de novo lipogenesis to insulin as a result of cell-autonomous down-regulation of InsR number in response to chronic hyperinsulinemia. We demonstrate in mouse primary hepatocytes that chronic hyperinsulinemia abrogates insulin's inhibition of glucose production, but not its stimulation of de novo lipogenesis. Using a competitive inhibitor of InsR, we show that there is a 4-fold difference between levels of InsR inhibition required to cause resistance of glucose production versus lipogenesis to the actions of insulin. Our data support a parsimonious model in which differential InsR activation underlies the selective IR of glucose production relative to lipogenesis, but both processes require signaling through Akt1/2.

Growth arrest and DNA damage-inducible 34 regulates liver regeneration in hepatic steatosis in mice.

UNLABELLED: The liver has robust regenerative potential in response to damage, but hepatic steatosis (HS) weakens this potential. We found that the enhanced integrated stress response (ISR) mediated by phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2α) impairs regeneration in HS and that growth arrest and DNA damage-inducible 34 (Gadd34)-dependent suppression of ISR plays a crucial role in fatty liver regeneration. Although mice fed a high-fat diet for 2 weeks developed moderate fatty liver with no increase in eIF2α phosphorylation before 70% hepatectomy, they showed impaired liver regeneration as a result of reduced proliferation and increased death of hepatocytes with increased phosphorylation of eIF2α and ISR. An increased ISR through Gadd34 knockdown induced C/EBP homologous protein (CHOP)-dependent apoptosis and receptor-interacting protein kinase 3-dependent necrosis, resulting in increased hepatocyte death during fatty liver regeneration. Furthermore, Gadd34 knockdown and increased phosphorylation of eIF2α decreased cyclin D1 protein and reduced hepatocyte proliferation. In contrast, enhancement of Gadd34 suppressed phosphorylation of eIF2α and reduced CHOP expression and hepatocyte apoptosis without affecting hepatocyte proliferation, clearly improving fatty liver regeneration. In more severe fatty liver of leptin receptor-deficient db/db mice, forced expression of hepatic Gadd34 also promoted hepatic regeneration after hepatectomy. CONCLUSION: Gadd34-mediated regulation of ISR acts as a physiological defense mechanism against impaired liver regeneration resulting from steatosis and is thus a possible therapeutic target for impaired regeneration in HS.

Compensatory hyperinsulinemia in high-fat diet-induced obese mice is associated with enhanced insulin translation in islets.

A high-fat diet (HF) is associated with obesity, insulin resistance, and hyperglycemia. Animal studies have shown compensatory mechanisms in pancreatic ß-cells after high fat load, such as increased pancreatic ß-cell mass, enhanced insulin secretion, and exocytosis. However, the effects of high fat intake on insulin synthesis are obscure. Here, we investigated whether insulin synthesis was altered in correlation with an HF diet, for the purpose of obtaining further understanding of the compensatory mechanisms in pancreatic ß-cells. Mice fed an HF diet are obese, insulin resistant, hyperinsulinemic, and glucose intolerant. In islets of mice fed an HF diet, more storage of insulin was identified. We analyzed insulin translation in mouse islets, as well as in INS-1 cells, using non-radioisotope chemicals. We found that insulin translational levels were significantly increased in islets of mice fed an HF diet to meet systemic demand, without altering its transcriptional levels. Our data showed that not only increased pancreatic ß-cell mass and insulin secretion but also elevated insulin translation is the major compensatory mechanism of pancreatic ß-cells.

Ablation of PDK1 in pancreatic beta cells induces diabetes as a result of loss of beta cell mass.

The total mass of islets of Langerhans is reduced in individuals with type 2 diabetes, possibly contributing to the pathogenesis of this condition. Although the regulation of islet mass is complex, recent studies have suggested the importance of a signaling pathway that includes the insulin or insulin-like growth factor-1 receptors, insulin receptor substrate and phosphatidylinositol (PI) 3-kinase. 3-Phosphoinositide-dependent protein kinase 1 (PDK1) is a serine-threonine kinase that mediates signaling downstream of PI 3-kinase. Here we show that mice that lack PDK1 specifically in pancreatic beta cells (betaPdk1-/- mice) develop progressive hyperglycemia as a result of a loss of islet mass. The mice show reductions in islet density as well as in the number and size of cells. Haploinsufficiency of the gene for the transcription factor Foxo1 resulted in a marked increase in the number, but not the size, of cells and resulted in the restoration of glucose homeostasis in betaPdk1-/- mice. These results suggest that PDK1 is important in maintenance of pancreatic cell mass and glucose homeostasis.

A High Fibrosis-4 Index is Associated with a Reduction in the Estimated Glomerular Filtration Rate in Non-obese Japanese Patients with Type 2 Diabetes Mellitus.

Liver fibrosis is associated with non-alcoholic fatty liver disease (NAFLD), and one of the most important risk factors for NAFLD is type 2 diabetes (T2DM). The Fibrosis-4 (FIB-4) index, a noninvasive liver fibrosis score, has been found to be useful for estimating liver fibrosis. Because individuals with non-obese NAFLD were recently reported to be metabolically unhealthy and have a higher risk of T2DM than individuals with obese NAFLD, we hypothesized that the clinical factors related to a high FIB-4 index would differ between non-obese and obese Japanese T2DM patients. Accordingly, we examined the relationship between clinical factors and the FIB-4 index in non-obese and obese Japanese patients with T2DM. We divided 265 patients into two groups by BMI level - a non-obese group (n = 149) and an obese group (n = 116) - and examined the correlation between the FIB-4 index and clinical parameters. Single regression analysis revealed that a high FIB-4 index was correlated with a reduction in the estimated glomerular filtration rate and hypertension in the non-obese group. Importantly, multiple regression analysis showed that only a reduction in the estimated glomerular filtration rate was significantly associated with a high FIB-4 index in the non-obese group. These results demonstrated that non-obese T2DM patients with a high FIB-4 index might be at risk of kidney dysfunction. Our findings may enable the more appropriate treatment of T2DM patients based on BMI level.

Association of short-term changes in HbA1c with body composition and the importance of muscle maintenance in patients with Type 2 diabetes.

AIMS: This study aimed to investigate the relationship between changes in glucose metabolism and body composition in patients with diabetes. METHODS: We included 380 patients with type 2 diabetes, who underwent bioelectrical impedance analysis, in this longitudinal study. Changes in HbA1c (ΔHbA1c) levels and body composition indices were compared between baseline and 6 months. A multivariate analysis was performed to examine the relationship between ΔHbA1c and changes in body composition. RESULTS: HbA1c levels were significantly decreased at 6 months (P < 0.01), but there was no significant change in BMI. A linear multiple regression analysis showed that ΔHbA1c was negatively correlated with changes in muscle mass (ß = -0.18; P = 0.047) and bone mineral content (ß = -0.28; P < 0.001), but there was no significant association between ΔHbA1c levels and a change in body fat percentage. CONCLUSIONS: This study shows a limited association between short-term changes in glucose metabolism and changes in body composition in patients with type 2 diabetes. Therefore, interventions aimed at reducing adiposity may not affect glucose metabolism in the short term, while interventions focused on maintaining or enhancing muscle mass and bone mineral content may play an important role in diabetes management.

Dietary Intervention for Control of Clinical Symptom in Patients with Systemic Metal Allergy: A Single Center Randomized Controlled Clinical Study.

Patients with eczema with a systemic metal allergy, such as nickel (Ni), cobalt (Co), chromium (Cr), and tin (Sn), should pay attention to symptomatic exacerbation by excessive metal intake in food. However, dietary intervention for systemic metal allergy can be difficult. In this study, we evaluated the effect of dietary intervention by a registered dietitian on clinical symptoms in patients with a systemic metal allergy. Forty-four patients with cutaneous symptoms who were diagnosed with a metal allergy were randomly assigned to the dietary intervention group (DI group, n = 29) by a registered dietitian or the control group (C group, n = 15). The DI group was individually instructed by a registered dietitian how to implement a metal-restricted diet and then evaluated 1 month later. Dermatologists treated skin lesions of patients in both groups. Skin symptoms assessed by the Severity Scoring of Atopic Dermatitis (SCORAD) index, blood tests, and urinary metal excretion were evaluated. The DI group showed decreased Ni, Co, Cr, and Sn intake (all P ≤ 0.05), and an improved total SCORAD score, eczema area, erythema, edema/papulation, oozing/crust, excoriation, lichenization and dryness after 1 month of intervention compared with before the intervention (all P ≤ 0.05). However, the C group showed decreased Ni and Sn intake and an improved oozing/crust score (all P < 0.05). It showed the effective reduction of dietary metal intake controls dermatitis due to a metal allergy. In conclusion, dietary intervention by a registered dietitian is effective in improving skin symptoms with a reduction in metal intake.

The structure of SrTiO3(001)-2 × 1 surface analyzed by high-resolution medium energy ion scattering coupled with ab initio calculations.

High-resolution medium energy ion scattering (MEIS) spectrometry coupled with photoelectron spectroscopy revealed unambiguously that the initial SrTiO3(001) surface chemically etched in a buffered NH4F-HF solution was perfectly terminated with a single-layer (SL) of TiO2(001) and annealing the surface at 600-800 [ordinal indicator, masculine]C in ultrahigh vacuum (UHV) led to a (2 × 1)-reconstructed surface terminated with a double-layer (DL) of TiO2(001). After annealing in UHV, rock-salt SrO(001) clusters with two atomic layer height grew epitaxially on the DL-TiO2(001)-2 × 1 surface with a coverage of 20%-30%. High-resolution MEIS in connection with ab initio calculations demonstrated the structure of the DL-TiO2(001)-2 × 1 surface close to that proposed by Erdman et al. [Nature (London) 419, 55 (2002)] rather than that predicted by Herger et al. [Phys. Rev. Lett. 98, 076102 (2007)]. Based on the MEIS analysis combined with the ab initio calculations, we propose the most probable (2 × 1) surface structure.

CEACAM1 regulates insulin clearance in liver.

We hypothesized that insulin stimulates phosphorylation of CEACAM1 which in turn leads to upregulation of receptor-mediated insulin endocytosis and degradation in the hepatocyte. We have generated transgenic mice over-expressing in liver a dominant-negative, phosphorylation-defective S503A-CEACAM1 mutant. Supporting our hypothesis, we found that S503A-CEACAM1 transgenic mice developed hyperinsulinemia resulting from impaired insulin clearance. The hyperinsulinemia caused secondary insulin resistance with impaired glucose tolerance and random, but not fasting, hyperglycemia. Transgenic mice developed visceral adiposity with increased amounts of plasma free fatty acids and plasma and hepatic triglycerides. These findings suggest a mechanism through which insulin signaling regulates insulin sensitivity by modulating hepatic insulin clearance.

[Progress in diabetes].

Type 2 diabetes mellitus is characterized by insulin resistance and pancreatic beta-cell failure. Pancreatic beta-cell failure plays an important role in the pathogenesis of diabetes in Japanese subjects. Several mechanisms underlying the causes of pancreatic beta-cell failure have been reported, including decreased insulin signaling, endoplasmic reticulum stress, oxidative stress, and inflammation. In addition, the role of epigenetics in this association has recently been highlighted. Intrauterine growth retardation (IUGR) leads to many disorders after maturation, such as obesity, glucose intolerance, and osteoporosis. IUGR also reduces pancreatic / cell mass. One of the underlying mechanisms is epigenetic modification, such as the reduction of histone acetylation and increase of methylation in the promoter region of the Pdx1 gene, which encodes an important transcription factor for pancreatic beta-cell function, leading to the reduction of Pdx1 expression levels. Numerous susceptibility genes for type 2 diabetes, including KCNQ1, have been identified in humans using genome-wide analyses and other related studies. The Kcnq1 locus is an imprinting gene. Noncoding RNA Kcnq1ot1 is expressed from the Kcnq1 locus and regulates the expression of neighboring genes on the paternal allele. We found that disruption of Kcnq1 results in reduced expression of Kcnqlot1 as well as increased expression of Cdkn1c, an imprinted gene that encodes a cell cycle inhibitor only when the mutation is on the paternal allele. Furthermore, histone modification in the Cdkn1c promoter region in pancreatic islets was found to contribute to this phenomenon. These results indicate that epigenetic modification might be important for the regulation of pancreatic beta-cell mass and the onset of diabetes.

Chlorogenic Acid and Caffeine in Coffee Restore Insulin Signaling in Pancreatic Beta Cells.

The incidence of type 2 diabetes is reported to be lower in frequent coffee drinkers than in non-coffee drinkers. To elucidate the mechanism by which coffee prevents the onset of type 2 diabetes, we analyzed how caffeine and chlorogenic acid, which are components of coffee, alter insulin signaling in MIN6 cells, a mouse pancreatic Β cell line. The results showed that caffeine improved insulin signaling under endoplasmic reticulum stress, and chlorogenic acid protected pancreatic Β cells by enhancing the expression of insulin receptor substrate 2 via cAMP response element-binding protein and promoting insulin signaling downstream of insulin receptor substrate 2. In addition, chlorogenic acid was a potent antioxidant for the protection of pancreatic Β cells. Furthermore, in vivo and in vitro analyses revealed that the pancreatic Β cell-protective effect of chlorogenic acid was mediated by the alleviation of endoplasmic reticulum stress. The results suggest that these components of coffee have the potential to reduce the pathogenesis of type 2 diabetes and improve pancreatic Β cell insufficiency.

Hepatic FASN deficiency differentially affects nonalcoholic fatty liver disease and diabetes in mouse obesity models.

Nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes are interacting comorbidities of obesity, and increased hepatic de novo lipogenesis (DNL), driven by hyperinsulinemia and carbohydrate overload, contributes to their pathogenesis. Fatty acid synthase (FASN), a key enzyme of hepatic DNL, is upregulated in association with insulin resistance. However, the therapeutic potential of targeting FASN in hepatocytes for obesity-associated metabolic diseases is unknown. Here, we show that hepatic FASN deficiency differentially affects NAFLD and diabetes depending on the etiology of obesity. Hepatocyte-specific ablation of FASN ameliorated NAFLD and diabetes in melanocortin 4 receptor-deficient mice but not in mice with diet-induced obesity. In leptin-deficient mice, FASN ablation alleviated hepatic steatosis and improved glucose tolerance but exacerbated fed hyperglycemia and liver dysfunction. The beneficial effects of hepatic FASN deficiency on NAFLD and glucose metabolism were associated with suppression of DNL and attenuation of gluconeogenesis and fatty acid oxidation, respectively. The exacerbation of fed hyperglycemia by FASN ablation in leptin-deficient mice appeared attributable to impairment of hepatic glucose uptake triggered by glycogen accumulation and citrate-mediated inhibition of glycolysis. Further investigation of the therapeutic potential of hepatic FASN inhibition for NAFLD and diabetes in humans should thus consider the etiology of obesity.

Deletion of Cdkn1b ameliorates hyperglycemia by maintaining compensatory hyperinsulinemia in diabetic mice.

The protein p27(Kip1) regulates cell cycle progression in mammals by inhibiting the activity of cyclin-dependent kinases (CDKs). Here we show that p27(Kip1) progressively accumulates in the nucleus of pancreatic beta cells in mice that lack either insulin receptor substrate 2 (Irs2(-/-)) or the long form of the leptin receptor (Lepr(-/-) or db/db). Deletion of the gene encoding p27(Kip1) (Cdkn1b) ameliorated hyperglycemia in these animal models of type 2 diabetes mellitus by increasing islet mass and maintaining compensatory hyperinsulinemia, effects that were attributable predominantly to stimulation of pancreatic beta-cell proliferation. Thus, p27(Kip1) contributes to beta-cell failure during the development of type 2 diabetes in Irs2(-/-) and Lepr(-/-) mice and represents a potential new target for the treatment of this condition.

XRCC3 gene polymorphism is associated with survival in Japanese lung cancer patients.

We focused on OGG1 Ser326Cys, MUTYH Gln324His, APEX1 Asp148Glu, XRCC1 Arg399Gln, and XRCC3 Thr241Met and examined the relationship between the different genotypes and survival of Japanese lung cancer patients. A total of 99 Japanese lung cancer patients were recruited into our study. Clinical data were collected, and genotypes of the target genes were identified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Survival analysis to verify the impact of these gene polymorphisms on the clinical outcome of lung cancer showed that lung squamous cell carcinoma patients with the Thr/Met genotype at XRCC3 had a significantly shorter survival time than those with the Thr/Thr genotype (13 months versus 48 months; log-rank test, p < 0.0001). Cox regression analysis showed that the carriers of XRCC3 genotypes were at a significantly higher risk [adjusted hazard ratio (HR) = 9.35, 95% confidence interval (CI) = 2.52-34.68, p = 0.001; adjusted HR = 9.05, 95% CI = 1.89-44.39, p = 0.006]. Our results suggest that XRCC3 Thr241Met may act as a favorable prognostic indicator for lung squamous cell carcinoma patients.