Long non-coding RNAs: the tentacles of chromatin remodeler complexes.

Chromatin remodeler complexes regulate gene transcription, DNA replication and DNA repair by changing both nucleosome position and post-translational modifications. The chromatin remodeler complexes are categorized into four families: the SWI/SNF, INO80/SWR1, ISWI and CHD family. In this review, we describe the subunits of these chromatin remodeler complexes, in particular, the recently identified members of the ISWI family and novelties of the CHD family. Long non-coding (lnc) RNAs regulate gene expression through different epigenetic mechanisms, including interaction with chromatin remodelers. For example, interaction of lncBRM with BRM inhibits the SWI/SNF complex associated with a differentiated phenotype and favors assembly of a stem cell-related SWI/SNF complex. Today, over 50 lncRNAs have been shown to affect chromatin remodeler complexes and we here discuss the mechanisms involved.

Alternative human liver transcripts of TCF7L2 bind to the gluconeogenesis regulator HNF4α at the protein level.

AIMS/HYPOTHESIS: Gene polymorphisms of TCF7L2 are associated with increased risk of type 2 diabetes and transcription factor 7-like 2 (TCF7L2) plays a role in hepatic glucose metabolism. We therefore addressed the impact of TCF7L2 isoforms on hepatocyte nuclear factor 4α (HNF4α) and the regulation of gluconeogenesis genes. METHODS: Liver TCF7L2 transcripts were analysed by quantitative PCR in 33 non-diabetic and 31 type 2 diabetic obese individuals genotyped for TCF7L2 rs7903146. To analyse transcriptional regulation by TCF7L2, small interfering RNA transfection, luciferase reporter and co-immunoprecipitation assays were performed in human hepatoma HepG2 cells. RESULTS: In livers of diabetic compared with normoglycaemic individuals, five C-terminal TCF7L2 transcripts showed increased expression. The type 2 diabetes risk allele of rs7903146 positively correlated with TCF7L2 expression in livers from normoglycaemic individuals only. In HepG2 cells, transcript and TCF7L2 protein levels were increased upon incubation in high glucose and insulin. Of the exon 13 transcripts, six were increased in a glucose dose-responsive manner. TCF7L2 transcriptionally regulated 29 genes related to glucose metabolism, including glucose-6-phosphatase. In cultured HepG2 cells, TCF7L2 did not regulate HNF4Α and FOXO1 transcription, but did affect HNF4α protein expression. The TCF7L2 isoforms T6 and T8 (without exon 13 and with exon 15/14, respectively) specifically interacted with HNF4α. CONCLUSIONS/INTERPRETATION: The different levels of expression of alternative C-terminal TCF7L2 transcripts in HepG2 cells, in livers of normoglycaemic individuals carrying the rs7901346 type 2 diabetes risk allele and in livers of diabetic individuals suggest that these transcripts play a role in the pathophysiology of type 2 diabetes. We also report for the first time a protein interaction in HepG2 cells between HNF4α and the T6 and T8 isoforms of TCF7L2, which suggests a distinct role for these specific alternative transcripts.

Fenofibrate inhibits endothelin-1 expression by peroxisome proliferator-activated receptor α-dependent and independent mechanisms in human endothelial cells.

OBJECTIVE: Dyslipidemia contributes to endothelial dysfunction in type 2 diabetes mellitus. Fenofibrate (FF), a ligand of the peroxisome proliferator-activated receptor-α (PPARα), has beneficial effects on microvascular complications. FF may act on the endothelium by regulating vasoactive factors, including endothelin-1 (ET-1). In vitro, FF decreases ET-1 expression in human microvascular endothelial cells. We investigated the molecular mechanisms involved in the effect of FF treatment on plasma levels of ET-1 in type 2 diabetes mellitus patients. METHODS AND RESULTS: FF impaired the capacity of transforming growth factor-ß to induce ET-1 gene expression. PPARα activation by FF increased expression of the transcriptional repressor Krüppel-like factor 11 and its binding to the ET-1 gene promoter. Knockdown of Krüppel-like factor 11 expression potentiated basal and transforming growth factor-ß-stimulated ET-1 expression, suggesting that Krüppel-like factor 11 downregulates ET-1 expression. FF, in a PPARα-independent manner, and insulin enhanced glycogen synthase kinase-3ß phosphorylation thus reducing glycogen synthase kinase-3 activity that contributes to the FF-mediated reduction of ET-1 gene expression. In type 2 diabetes mellitus, improvement of flow-mediated dilatation of the brachial artery by FF was associated with a decrease in plasma ET-1. CONCLUSIONS: FF decreases ET-1 expression by a PPARα-dependent mechanism, via transcriptional induction of the Krüppel-like factor 11 repressor and by PPARα-independent actions via inhibition of glycogen synthase kinase-3 activity.

TCF7L2 splice variants have distinct effects on beta-cell turnover and function.

Type 2 diabetes manifests when the ß-cell fails to secrete sufficient amounts of insulin to maintain normoglycemia and undergoes apoptosis. The disease progression results from an interplay of environmental factors and genetic predisposition. Polymorphisms in T-cell factor 7-like 2 (TCF7L2) strongly correlate with type 2 diabetes mellitus (T2DM). While TCF7L2 mRNA is upregulated in islets in diabetes, protein levels are downregulated. The loss of TCF7L2 induces impaired function and apoptosis. By analyzing human isolated islets, we provide three explanations for this opposite regulation and the mechanisms of TCF7L2 on ß-cell function and survival. (i) We found TCF7L2 transcripts in the human ß-cell, which had opposite effects on ß-cell survival, function and Wnt signaling activation. While TCF7L2 clone B1, which lacks exons 13, 14, 15 and 16 induced ß-cell apoptosis, impaired function and inhibited glucagon-like peptide 1 response and downstream targets of Wnt signaling, clones B3 and B7 which both contain exon 13, improved ß-cell survival and function and activated Wnt signaling. (ii) TCF7L2 mRNA is extremely unstable and is rapidly degraded under pro-diabetic conditions and (iii) TCF7L2 depletion in islets induced activation of glycogen synthase kinase 3-ß, but this was independent of endoplasmic reticulum stress. We demonstrated function-specific transcripts of TCF7L2, which possessed distinct physiological and pathophysiological effects on the ß-cell. The presence of deleterious TCF7L2 splice variants may be a mechanism of ß-cell failure in T2DM.

Peroxisome proliferator-activated receptor-γ activation induces 11ß-hydroxysteroid dehydrogenase type 1 activity in human alternative macrophages.

OBJECTIVE: 11ß-Hydroxysteroid dehydrogenase type 1 (11ß-HSD1) catalyzes the intracellular reduction of inactive cortisone to active cortisol, the natural ligand activating the glucocorticoid receptor (GR). Peroxisome proliferator- activated receptor-γ (PPARγ) is a nuclear receptor controlling inflammation, lipid metabolism, and the macrophage polarization state. In this study, we investigated the impact of macrophage polarization on the expression and activity of 11ß-HSD1 and the role of PPARγ therein. METHODS AND RESULTS: 11ß-HSD1 gene expression is higher in proinflammatory M1 and anti-inflammatory M2 macrophages than in resting macrophages, whereas its activity is highest in M2 macrophages. Interestingly, PPARγ activation induces 11ß-HSD1 enzyme activity in M2 macrophages but not in resting macrophages or M1 macrophages. Consequently, human M2 macrophages displayed enhanced responsiveness to the 11ß-HSD1 substrate cortisone, an effect amplified by PPARγ induction of 11ß-HSD1 activity, as illustrated by an increased expression of GR target genes. CONCLUSION: Our data identify a positive cross-talk between PPARγ and GR in human M2 macrophages via the induction of 11ß-HSD1 expression and activity.

Disruption of a novel Kruppel-like transcription factor p300-regulated pathway for insulin biosynthesis revealed by studies of the c.-331 INS mutation found in neonatal diabetes mellitus.

Krüppel-like transcription factors (KLFs) have elicited significant attention because of their regulation of essential biochemical pathways and, more recently, because of their fundamental role in the mechanisms of human diseases. Neonatal diabetes mellitus is a monogenic disorder with primary alterations in insulin secretion. We here describe a key biochemical mechanism that underlies neonatal diabetes mellitus insulin biosynthesis impairment, namely a homozygous mutation within the insulin gene (INS) promoter, c.-331C>G, which affects a novel KLF-binding site. The combination of careful expression profiling, electromobility shift assays, reporter experiments, and chromatin immunoprecipitation demonstrates that, among 16 different KLF proteins tested, KLF11 is the most reliable activator of this site. Congruently, the c.-331C>G INS mutation fails to bind KLF11, thus inhibiting activation by this transcription factor. Klf11(-/-) mice recapitulate the disruption in insulin production and blood levels observed in patients. Thus, these data demonstrate an important role for KLF11 in the regulation of INS transcription via the novel c.-331 KLF site. Lastly, our screening data raised the possibility that other members of the KLF family may also regulate this promoter under distinct, yet unidentified, cellular contexts. Collectively, this study underscores a key role for KLF proteins in biochemical mechanisms of human diseases, in particular, early infancy onset diabetes mellitus.

Mucin expression, epigenetic regulation and patient survival: A toolkit of prognostic biomarkers in epithelial cancers.

Twenty mucin genes have been identified and classified in two groups (encoding secreted and membrane-bound proteins). Secreted mucins participate in mucus formation by assembling a 3-dimensional network via oligomerization, whereas membrane-bound mucins are anchored to the outer membrane mediating extracellular interactions and cell signaling. Both groups have been associated with carcinogenesis progression in epithelial cancers, and are therefore considered as potential therapeutic targets. In the present review, we discuss the link between mucin expression patterns and patient survival and propose mucins as prognosis biomarkers of epithelial cancers (esophagus, gastric, pancreatic, colorectal, lung, breast or ovarian cancers). We also investigate the relationship between mucin expression and overall survival in the TCGA dataset. In particular, epigenetic mechanisms regulating mucin gene expression, such as aberrant DNA methylation and histone modification, are interesting as they are also associated with diagnosis or prognosis significance. Indeed, mucin hypomethylation has been shown to be associated with carcinogenesis progression and was linked to prognosis in colon cancer or pancreatic cancer patients. Finally we describe the relationship between mucin expression and non-coding RNAs that also may serve as biomarkers. Altogether the concomitant knowledge of specific mucin-pattern expression and epigenetic regulation could be translated as biomarkers with a better specificity/sensitivity performance in several epithelial cancers.

Antagonistic Roles of the Tumor Suppressor miR-210-3p and Oncomucin MUC4 Forming a Negative Feedback Loop in Pancreatic Adenocarcinoma.

BACKGROUND: Pancreatic adenocarcinoma (PDAC) is a deadly cancer with an extremely poor prognosis. MUC4 membrane-bound mucin is neoexpressed in early pancreatic neoplastic lesions and is associated with PDAC progression and chemoresistance. In cancers, microRNAs (miRNAs, small noncoding RNAs) are crucial regulators of carcinogenesis, chemotherapy response and even metastatic processes. In this study, we aimed at identifying and characterizing miRNAs activated downstream of MUC4-associated signaling in pancreatic adenocarcinoma. MiRnome analysis comparing MUC4-KD versus Mock cancer cells showed that MUC4 inhibition impaired miR-210-3p expression. Therefore, we aimed to better understand the miR-210-3p biological roles. METHODS: miR-210-3p expression level was analyzed by RT-qPCR in PDAC-derived cell lines (PANC89 Mock and MUC4-KD, PANC-1 and MiaPACA-2), as well as in mice and patients tissues. The MUC4-miR-210-3p regulation was investigated using luciferase reporter construct and chromatin immunoprecipitation experiments. Stable cell lines expressing miR-210-3p or anti-miR-210-3p were established using CRISPR/Cas9 technology or lentiviral transduction. We evaluated the biological activity of miR-210-3p in vitro by measuring cell proliferation and migration and in vivo using a model of subcutaneous xenograft. RESULTS: miR-210-3p expression is correlated with MUC4 expression in PDAC-derived cells and human samples, and in pancreatic PanIN lesions of Pdx1-Cre; LstopL-KrasG12D mice. MUC4 enhances miR-210-3p expression levels via alteration of the NF-κB signaling pathway. Chromatin immunoprecipitation experiments showed p50 NF-κB subunit binding on miR-210-3p promoter regions. We established a reciprocal regulation since miR-210-3p repressed MUC4 expression via its 3'-UTR. MiR-210-3p transient transfection of PANC89, PANC-1 and MiaPACA-2 cells led to a decrease in cell proliferation and migration. These biological effects were validated in cells overexpressing or knocked-down for miR-210-3p. Finally, we showed that miR-210-3p inhibits pancreatic tumor growth and proliferation in vivo. CONCLUSION: We identified a MUC4-miR-210-3p negative feedback loop in early-onset PDAC, but also revealed new functions of miR-210-3p in both in vitro and in vivo proliferation and migration of pancreatic cancer cells, suggesting a complex balance between MUC4 pro-oncogenic roles and miR-210-3p anti-tumoral effects.

MODY7 gene, KLF11, is a novel p300-dependent regulator of Pdx-1 (MODY4) transcription in pancreatic islet beta cells.

Pdx-1 (pancreatic-duodenal homeobox-1), a MODY4 homeodomain transcription factor, serves as a master regulator in the pancreas because of its importance during organogenesis and in adult islet insulin-producing beta cell activity. Here, we show that KLF11, an SP/Krüppel-like (SP/KLF) transcription factor, mutated in French maturity onset diabetes of the young patients (MODY7), regulates Pdx-1 transcription in beta cells through two evolutionarily conserved GC-rich motifs in conserved Area II, a control region essential to islet beta cell-enriched expression. These regulatory elements, termed GC1 (human base pair -2061/-2055) and GC2 (-2036/-2027), are also nearly identical to the consensus KLF11 binding sequence defined here by random oligonucleotide binding analysis. KLF11 specifically associates with Area II in chromatin immunoprecipitation assays, while preventing binding to GC1- and/or GC2-compromised Pdx1-driven reporter activity in beta cell lines. Mechanistically, we find that KLF11 interacts with the coactivator p300 via its zinc finger domain in vivo to mediate Pdx-1 activation. Together, our data identified a hierarchical regulatory cascade for these two MODY genes, suggesting that gene regulation in MODY is more complex than anticipated previously. Furthermore, because KLF11 like most MODY-associated transcription factors uses p300, these data further support a role for this coactivator as a critical chromatin link in forms of type 2 diabetes.

Unsupervised Hierarchical Clustering of Pancreatic Adenocarcinoma Dataset from TCGA Defines a Mucin Expression Profile that Impacts Overall Survival.

Mucins are commonly associated with pancreatic ductal adenocarcinoma (PDAC) that is a deadly disease because of the lack of early diagnosis and efficient therapies. There are 22 mucin genes encoding large O-glycoproteins divided into two major subgroups: membrane-bound and secreted mucins. We investigated mucin expression and their impact on patient survival in the PDAC dataset from The Cancer Genome Atlas (PAAD-TCGA). We observed a statistically significant increased messenger RNA (mRNA) relative level of most of the membrane-bound mucins (MUC1/3A/4/12/13/16/17/20), secreted mucins (MUC5AC/5B), and atypical mucins (MUC14/18) compared to normal pancreas. We show that MUC1/4/5B/14/17/20/21 mRNA levels are associated with poorer survival in the high-expression group compared to the low-expression group. Using unsupervised clustering analysis of mucin gene expression patterns, we identified two major clusters of patients. Cluster #1 harbors a higher expression of MUC15 and atypical MUC14/MUC18, whereas cluster #2 is characterized by a global overexpression of membrane-bound mucins (MUC1/4/16/17/20/21). Cluster #2 is associated with shorter overall survival. The patient stratification appears to be independent of usual clinical features (tumor stage, differentiation grade, lymph node invasion) suggesting that the pattern of membrane-bound mucin expression could be a new prognostic marker for PDAC patients.

Colon cancer stemness as a reversible epigenetic state: Implications for anticancer therapies.

The recent discovery of cancer cell plasticity, i.e. their ability to reprogram into cancer stem cells (CSCs) either naturally or under chemotherapy and/or radiotherapy, has changed, once again, the way we consider cancer treatment. If cancer stemness is a reversible epigenetic state rather than a genetic identity, opportunities will arise for therapeutic strategies that remodel epigenetic landscapes of CSCs. However, the systematic use of DNA methyltransferase and histone deacetylase inhibitors, alone or in combination, in advanced solid tumors including colorectal cancers, regardless of their molecular subtypes, does not seem to be the best strategy. In this review, we first summarize the knowledge researchers have gathered on the epigenetic signatures of CSCs with the difficulty of isolating rare populations of cells. We raise questions about the relevant use of currently available epigenetic inhibitors (epidrugs) while the expression of numerous cancer stem cell markers are often repressed by epigenetic mechanisms. These markers include the three cluster of differentiation CD133, CD44 and CD166 that have been extensively used for the isolation of colon CSCs.and . Finally, we describe current treatment strategies using epidrugs, and we hypothesize that, using correlation tools comparing associations of relevant CSC markers with chromatin modifier expression, we could identify better candidates for epienzyme targeting.

Genetic analysis of Kruppel-like zinc finger 11 variants in 5864 Danish individuals: potential effect on insulin resistance and modified signal transducer and activator of transcription-3 binding by promoter variant -1659G>C.

CONTEXT: The transcription factor Krüppel-like zinc finger 11 (KLF11) has been suggested to contribute to genetic risk of type 2 diabetes (T2D). Our previous results showed that four KLF11 variants, in strong linkage disequilibrium (LD block including +185 A>G/Gln62Arg and -1659 G>C) were associated with T2D in a north European case-control study. Here we further analyzed these variants for T2D association in a general Danish population and assess their possible effect on gene function. METHODS: We genotyped Gln62Arg variant, representative for the LD block, in 5864 subjects of the INTER99 study to assess association to T2D and glucose metabolism-related quantitative traits. We studied effects of LD-block variants on KLF11 function and in particular, the effect of -1659G>C on transcriptional regulation of KLF11 using EMSA, chromatin immunoprecipitation, gene reporter assays, and small interfering RNA transfection. RESULTS: We could not confirm T2D association of the KLF11 LD block, however, in glucose-tolerant subjects; it was significantly associated with higher fasting serum insulin and C-peptide levels and increased homeostasis model assessment insulin resistance indexes (P = 0.00004, P = 0.006, and P = 0.00002, respectively). In addition, binding of signal transducer and activator of transcription (STAT)-3 to the wild-type (-1659G>C) allele stimulated gene transcription, whereas STAT3 did not bind onto the mutant allele. CONCLUSIONS: We showed that KLF11 may interfere with glucose homeostasis in a Danish general population and that STAT3-mediated up-regulation of KLF11 transcription was impaired by the -1659G>C variant. Overall, KLF11 variants may have a deleterious effect on insulin sensitivity, although that may not be sufficient to lead to T2D.

Epigenetic Regulation by lncRNAs: An Overview Focused on UCA1 in Colorectal Cancer.

Colorectal cancers have become the second leading cause of cancer-related deaths. In particular, acquired chemoresistance and metastatic lesions occurring in colorectal cancer are a major challenge for chemotherapy treatment. Accumulating evidence shows that long non-coding (lncRNAs) are involved in the initiation, progression, and metastasis of cancer. We here discuss the epigenetic mechanisms through which lncRNAs regulate gene expression in cancer cells. In the second part of this review, we focus on the role of lncRNA Urothelial Cancer Associated 1 (UCA1) to integrate research in different types of cancer in order to decipher its putative function and mechanism of regulation in colorectal cancer cells. UCA1 is highly expressed in cancer cells and mediates transcriptional regulation on an epigenetic level through the interaction with chromatin modifiers, by direct regulation via chromatin looping and/or by sponging the action of a diversity of miRNAs. Furthermore, we discuss the role of UCA1 in the regulation of cell cycle progression and its relation to chemoresistance in colorectal cancer cells.

Analysis of KLF transcription factor family gene variants in type 2 diabetes.

BACKGROUND: The Krüppel-like factor (KLF) family consists of transcription factors that can activate or repress different genes implicated in processes such as differentiation, development, and cell cycle progression. Moreover, several of these proteins have been implicated in glucose homeostasis, making them candidate genes for involvement in type 2 diabetes (T2D). METHODS: Variants of nine KLF genes were genotyped in T2D cases and controls and analysed in a two-stage study. The first case-control set included 365 T2D patients with a strong family history of T2D and 363 normoglycemic individuals and the second set, 750 T2D patients and 741 normoglycemic individuals, all of French origin. The SNPs of six KLF genes were genotyped by Taqman SNP Genotyping Assays. The other three KLF genes (KLF2, -15 and -16) were screened and the identified frequent variants of these genes were analysed in the case-control studies. RESULTS: Three of the 28 SNPs showed a trend to be associated with T2D in our first case-control set (P < 0.10). These SNPs, located in the KLF2, KLF4 and KLF5 gene were then analysed in our second replication set, but analysis of this set and the combined analysis of the three variants in all 2,219 individuals did not show an association with T2D in this French population. As the KLF2, -15 and -16 variants were representative for the genetic variability in these genes, we conclude they do not contribute to genetic susceptibility for T2D. CONCLUSION: It is unlikely that variants in different members of the KLF gene family play a major role in T2D in the French population.

GAD2 on chromosome 10p12 is a candidate gene for human obesity.

The gene GAD2 encoding the glutamic acid decarboxylase enzyme (GAD65) is a positional candidate gene for obesity on Chromosome 10p11-12, a susceptibility locus for morbid obesity in four independent ethnic populations. GAD65 catalyzes the formation of gamma-aminobutyric acid (GABA), which interacts with neuropeptide Y in the paraventricular nucleus to contribute to stimulate food intake. A case-control study (575 morbidly obese and 646 control subjects) analyzing GAD2 variants identified both a protective haplotype, including the most frequent alleles of single nucleotide polymorphisms (SNPs) +61450 C>A and +83897 T>A (OR = 0.81, 95% CI [0.681-0.972], p = 0.0049) and an at-risk SNP (-243 A>G) for morbid obesity (OR = 1.3, 95% CI [1.053-1.585], p = 0.014). Furthermore, familial-based analyses confirmed the association with the obesity of SNP +61450 C>A and +83897 T>A haplotype (chi(2) = 7.637, p = 0.02). In the murine insulinoma cell line betaTC3, the G at-risk allele of SNP -243 A>G increased six times GAD2 promoter activity (p < 0.0001) and induced a 6-fold higher affinity for nuclear extracts. The -243 A>G SNP was associated with higher hunger scores (p = 0.007) and disinhibition scores (p = 0.028), as assessed by the Stunkard Three-Factor Eating Questionnaire. As GAD2 is highly expressed in pancreatic beta cells, we analyzed GAD65 antibody level as a marker of beta-cell activity and of insulin secretion. In the control group, -243 A>G, +61450 C>A, and +83897 T>A SNPs were associated with lower GAD65 autoantibody levels (p values of 0.003, 0.047, and 0.006, respectively). SNP +83897 T>A was associated with lower fasting insulin and insulin secretion, as assessed by the HOMA-B% homeostasis model of beta-cell function (p = 0.009 and 0.01, respectively). These data support the hypothesis of the orexigenic effect of GABA in humans and of a contribution of genes involved in GABA metabolism in the modulation of food intake and in the development of morbid obesity.

Beneficial metabolic effects of rapamycin are associated with enhanced regulatory cells in diet-induced obese mice.

The "mechanistic target of rapamycin" (mTOR) is a central controller of growth, proliferation and/or motility of various cell-types ranging from adipocytes to immune cells, thereby linking metabolism and immunity. mTOR signaling is overactivated in obesity, promoting inflammation and insulin resistance. Therefore, great interest exists in the development of mTOR inhibitors as therapeutic drugs for obesity or diabetes. However, despite a plethora of studies characterizing the metabolic consequences of mTOR inhibition in rodent models, its impact on immune changes associated with the obese condition has never been questioned so far. To address this, we used a mouse model of high-fat diet (HFD)-fed mice with and without pharmacologic mTOR inhibition by rapamycin. Rapamycin was weekly administrated to HFD-fed C57BL/6 mice for 22 weeks. Metabolic effects were determined by glucose and insulin tolerance tests and by indirect calorimetry measures of energy expenditure. Inflammatory response and immune cell populations were characterized in blood, adipose tissue and liver. In parallel, the activities of both mTOR complexes (e. g. mTORC1 and mTORC2) were determined in adipose tissue, muscle and liver. We show that rapamycin-treated mice are leaner, have enhanced energy expenditure and are protected against insulin resistance. These beneficial metabolic effects of rapamycin were associated to significant changes of the inflammatory profiles of both adipose tissue and liver. Importantly, immune cells with regulatory functions such as regulatory T-cells (Tregs) and myeloid-derived suppressor cells (MDSCs) were increased in adipose tissue. These rapamycin-triggered metabolic and immune effects resulted from mTORC1 inhibition whilst mTORC2 activity was intact. Taken together, our results reinforce the notion that controlling immune regulatory cells in metabolic tissues is crucial to maintain a proper metabolic status and, more generally, comfort the need to search for novel pharmacological inhibitors of the mTOR signaling pathway to prevent and/or treat metabolic diseases.

Role of transcription factor KLF11 and its diabetes-associated gene variants in pancreatic beta cell function.

KLF11 (TIEG2) is a pancreas-enriched transcription factor that has elicited significant attention because of its role as negative regulator of exocrine cell growth in vitro and in vivo. However, its functional role in the endocrine pancreas remains to be established. Here, we report, for the first time, to our knowledge, the characterization of KLF11 as a glucose-inducible regulator of the insulin gene. A combination of random oligonucleotide binding, EMSA, luciferase reporter, and chromatin immunoprecipitation assays shows that KLF11 binds to the insulin promoter and regulates its activity in beta cells. Genetic analysis of the KLF11 gene revealed two rare variants (Ala347Ser and Thr220Met) that segregate with diabetes in families with early-onset type 2 diabetes, and significantly impair its transcriptional activity. In addition, analysis of 1,696 type 2 diabetes mellitus and 1,776 normoglycemic subjects show a frequent polymorphic Gln62Arg variant that significantly associates with type 2 diabetes mellitus in North European populations (OR = 1.29, P = 0.00033). Moreover, this variant alters the corepressor mSin3A-binding activity of KLF11, impairs the activation of the insulin promoter and shows lower levels of insulin expression in pancreatic beta cells. In addition, subjects carrying the Gln62Arg allele show decreased plasma insulin after an oral glucose challenge. Interestingly, all three nonsynonymous KLF11 variants show increased repression of the catalase 1 promoter, suggesting a role in free radical clearance that may render beta cells more sensitive to oxidative stress. Thus, both functional and genetic analyses reveal that KLF11 plays a role in the regulation of pancreatic beta cell physiology, and its variants may contribute to the development of diabetes.