TCF7L2 Expression Research Articles

TCF7L2 Regulates Late Events in Insulin Secretion From Pancreatic Islet β-Cells

OBJECTIVEPolymorphisms in the human TCF7L2 gene are associated with reduced insulin secretion and an increased risk of type 2 diabetes. However, the mechanisms by which TCF7L2 affect insulin secretion are still unclear. We define the effects of TCF7L2 expression level on mature β-cell function and suggest a potential mechanism for its actions.RESEARCH DESIGN AND METHODSTCF7L2 expression in rodent islets and β-cell lines was altered using RNAi or adenoviral transduction. β-Cell gene profiles were measured by quantitative real-time PCR and the effects on intracellular signaling and exocytosis by live cell imaging, electron microscopy, and patch clamp electrophysiology.RESULTSReducing TCF7L2 expression levels by RNAi decreased glucose- but not KCl-induced insulin secretion. The glucose-induced increments in both ATP/ADP ratio and cytosolic free Ca2+ concentration ([Ca2+]i) were increased compared with controls. Overexpression of TCF7L2 exerted minor inhibitory effects on glucose-regulated changes in [Ca2+]i and insulin release. Gene expression profiling in TCF7L2-silenced cells revealed increased levels of mRNA encoding syntaxin 1A but decreased Munc18–1 and ZnT8 mRNA. Whereas the number of morphologically docked vesicles was unchanged by TCF7L2 suppression, secretory granule movement increased and capacitance changes decreased, indicative of defective vesicle fusion.CONCLUSION—TCF7L2 is involved in maintaining expression of β-cell genes regulating secretory granule fusion. Defective insulin exocytosis may thus underlie increased diabetes incidence in carriers of the at-risk TCF7L2 alleles.

Expression and molecular diversity of Tcf7l2 in the developing murine cerebellum and brain

The Wingless family of secreted proteins impinges on multiple aspects of vertebrate nervous system development, from early global patterning and cell fate decision to synaptogenesis. Here, we mapped the developmental expression of the Tcf7l2, which is key to the canonical Wingless signaling cascade, in the developing cerebellum. The exclusive and transient expression of Tcf7l2 in ventricular and Olig2-defined precursor cells within the cerebellar anlage, and its predominant expression in postmitotic neurons in the midbrain/inferior colliculus allowed us to ask whether cell type-specific differences are also reflected in splice isoform variability. We also included in this analysis intestinal epithelia, where Tcf7l2 function has been intensively studied. Our data reveal extensive variability of Tcf7l2 splicing in the central nervous system. Additional variability in brain-expressed Tcf7l2 is generated by a length polymorphism of expressed mRNAs in a stretch of normally nine adenines found at the beginning of exon 18, reminiscent of variability observed at the same site in cancers with microsatellite instability. A consensus emerging from our data is that the expression of isoforms comprising or lacking the C-clamp motif, which has been linked by in vitro studies to the regulation of cell growth, is indeed tightly correlated with the proliferative status in vivo.

No effect of cancer-associated SNP rs6983267 in the 8q24 region on co-expression of MYC and TCF7L2 in normal colon tissue

A single nucleotide polymorphism (SNP) rs6983267, located within the 8q24 region, is strongly associated with risk of colorectal and prostate cancer. It has been suggested that the mechanism of this association is related to differential interaction of TCF7L2 protein (previously known as TCF-4) with alleles of rs6983267, influencing the expression of a well-known oncogene, MYC, located 335 Kb telomeric. Here, we tested the correlation between mRNA expression of MYC and several alternatively spliced forms of TCF7L2 in 117 non-cancer colon samples. We observed a strong correlation (r = 0.60, p < 10-6) between expression of MYC and a unique splicing form of TCF7L2. The level of MYC expression in these samples was associated with expression of some TCF7L2 splicing forms but not with genotypes of rs6983267, or interaction of rs6983267 with TCF7L2 expression. These findings suggest that some splicing forms of TCF7L2 may be functionally important for regulation of MYC expression in colon tissue but this regulation is not directly dependent on rs6983267.

TCF7L2 gene expression in human visceral and subcutaneous adipose tissue is differentially regulated but not associated with type 2 diabetes mellitus

Variants in the TCF7L2 gene have been associated with type 2 diabetes mellitus (T2DM), but the causal variant(s) is still unknown. We studied the TCF7L2 messenger RNA (mRNA) expression in paired samples of visceral and subcutaneous adipose tissue from 49 subjects using quantitative real-time polymerase chain reaction and its relation to obesity and T2DM. All subjects were genotyped for the previously described TCF7L2 diabetes risk variants. Independent of age, sex, obesity, and diabetes status, we found >3-fold higher TCF7L2 mRNA expression in subcutaneous compared with visceral adipose tissue. There was no correlation between visceral and subcutaneous TCF7L2 expression. No differences in adipose tissue TCF7L2 mRNA expression levels were found between diabetic and nondiabetic subjects, or between lean and obese subjects (all Ps > .05). In addition, there was no association between TCF7L2 genetic variants and mRNA expression. Based on our data, TCF7L2 mRNA expression is fat-depot specific but does not seem to provide the mechanistic link explaining genetic association with T2DM.

Expression of the transcription factor 7-like 2 gene ( TCF7L2) in human adipocytes is down regulated by insulin

Variants in the TCF7L2 gene (transcription factor 7-like 2) have shown strong association with type 2 diabetes with two defined risk haplotypes, HapA and HapB T2D. TCF7L2 may play a role in both glucose homeostasis and adipogenesis. Our aim was to characterize the TCF7L2 mRNA expression and regulation in human adipose tissue. We quantified TCF7L2 mRNA levels in cultured human adipocytes and in biopsies from visceral (VAT) and subcutaneous (SAT) adipose tissue from 38 obese non-diabetic subjects, using real-time PCR. The influence of haplotype and clinical traits on TCF7L2 mRNA levels were investigated. In vitro, insulin decreased TCF7L2 mRNA expression. This effect was attenuated in cells incubated with the free fatty acids palmitate or oleate. In vivo, we found significantly higher expression in SAT from more insulin resistant subjects. No correlations between TCF7L2 mRNA expression and obesity measures were observed. TCF7L2 expression was higher in VAT than in SAT and when stratifying for haplotype, this difference was seen in HapA carriers but not in non-HapA carriers. In conclusion, TCF7L2 mRNA levels in adipocytes are decreased by insulin and seem to increase in insulin resistant subjects and in HapA carriers.

TCF7L2 is associated with high serum triacylglycerol and differentially expressed in adipose tissue in families with familial combined hyperlipidaemia

Common DNA variants of the transcription factor 7-like 2 gene (TCF7L2) are associated with type 2 diabetes. Familial combined hyperlipidaemia (FCHL) is characterised by hypertriacylglycerolaemia, hypercholesterolaemia, or both. Additionally, disturbances in glucose metabolism are commonly seen in FCHL. Therefore, we hypothesised that TCF7L2 may contribute to the genetic susceptibility for this common dyslipidaemia. We investigated the effect of the TCF7L2 variants, rs7903146 and rs12255372, on FCHL and its component traits triacylglycerol (TG), total cholesterol (TC) and apolipoprotein B (ApoB) in 759 individuals from 55 Mexican families. As a replication sample, 719 individuals from 60 Finnish FCHL families were analysed. We also used quantitative RT-PCR to evaluate the transcript levels of TCF7L2 in 47 subcutaneous fat biopsies from unrelated Mexican FCHL and normolipidaemic participants. Significant evidence for association was observed for high TG for the T alleles of rs7903146 and rs12255372 (p = 0.005 and p = 0.01) in Mexican FCHL families. No evidence for association was observed for FCHL, TC, ApoB or glucose in Mexicans. When testing rs7903146 and rs12255372 for replication in Finnish FCHL families, these single nucleotide polymorphisms were associated with TG (p = 0.01 and p = 0.007). Furthermore, we observed statistically significant decreases in the mRNA levels (p = 0.0002) of TCF7L2 in FCHL- and TG-affected individuals. TCF7L2 expression was not altered by the SNP genotypes. These data show that rs7903146 and rs12255372 are significantly associated with high TG in FCHL families from two different populations. In addition, significantly decreased expression of TCF7L2 was observed in TG- and FCHL-affected individuals.

Identification of members of the Wnt signaling pathway in the embryonic pituitary gland.

Prop1 is one of several transcription factors important for the development of the pituitary gland. Downstream targets of PROP1 and other critical pituitary transcription factors remain largely unknown. We have generated a partial expression profile of the developing pituitary gland containing over 350 transcripts, using cDNA subtractive hybridization between Prop1(df/df) and wild-type embryonic pituitary gland primordia. Numerous classes of genes including transcription factors, membrane associated molecules, and cell cycle regulators were identified in this study. Of the transcripts, 34% do not have sequence similarity to known genes, but are similar to ESTs, and 4% represent novel sequences. Pituitary gland expression of a number of clones was verified using in situ hybridization. Several members of the Wnt signaling pathway were identified in the developing pituitary gland. The frizzled2 receptor, Apc, beta-catenin, groucho, and a novel isoform of TCF4 (officially named Tcf7l2) were identified in developing pituitary libraries. Three N-terminal alternatively spliced Tcf7l2 isoforms are reported here, each of which lacks a DNA-binding domain. Functional studies indicate that these isoforms can act as endogenous inhibitors of Wnt signaling in some contexts. This is the first report of Tcf7l2 and Fzd2 expression in the developing pituitary. These molecules may be important in mediating Wnt signaling during pituitary ontogeny. We expect other transcripts from these libraries to be involved in pituitary gland development.