title: Functional analysis of TCF7L2 genetic variants associated with type 2 diabetes.
abstract: OBJECTIVE
  Common non-coding variations within the TCF7L2 locus have a strong influence on type 2 diabetes (T2D) susceptibility through uncharacterised mechanisms. An islet-specific functional polymorphism has been identified, although this does not explain the association between genotype and gene expression in other cell types. This study sought to identify these other functional TCF7L2 variants.
  
  
  RESULTS
  Alternative splicing and gene expression from TCF7L2 was examined from peripheral blood mononuclear cells from 100 healthy Caucasians using two T2D-associated SNPs, rs7903146 and rs12255372. Electrophoretic mobility shift assays and luciferase reporter assays were performed with these SNPs and those in strong LD to determine potential SNP functionality. Individuals homozygous for rs7903146 and rs12255372 T2D risk alleles (TT/TT) expressed 2.6-fold greater levels of TCF7L2 mRNA compared to individuals homozygous for the non-risk alleles (CC/GG, p = 0.006), although differentially spliced TCF7L2 transcripts did not differ by T2D risk-associated genotype. From SNPs identified to be in strong LD with the T2D-associated SNPs, rs7903146 and rs12255372, five (rs4132670, rs4506565, rs7903146, rs7901695, rs17747324) demonstrated allele-specific binding in electrophoretic mobility shift assays (EMSA). In luciferase reporter assays, rs4132670 exhibited 1.3-fold higher levels of enhancer activity in the Huh7 cell line (p = 3.8 × 10(-5)) and 2-fold higher levels in a WiDr colon carcinoma cell line (p = 0.008).
  
  
  CONCLUSIONS
  These results suggest that rs4132670, located in a region of chromatin accessibility, is a non-tissue-specific candidate functional SNP that has the potential to play a role in TCF7L2 gene expression and T2D risk.
authors.affiliation: BHF Centre for Cardiovascular Genetics, Department of Medicine, University College London, London, United Kingdom.
authors.forename: D X
authors.initials: DX
authors.lastname: Pang
authors.forename: A J P
authors.initials: AJ
authors.lastname: Smith
authors.forename: S E
authors.initials: SE
authors.lastname: Humphries
mesh_terms: D000483:Alleles; D017398:Alternative Splicing; D045744:Cell Line, Tumor; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics*; D005091:Exons; D015870:Gene Expression; D020022:Genetic Predisposition to Disease; D006720:Homozygote; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012307:Risk Factors; D058118:Transcription Factor 7-Like 2 Protein / Q000235:genetics* / Q000378:metabolism; D044465:White People / Q000235:genetics
chemical_list: D012333:RNA, Messenger; C544894:TCF7L2 protein, human; D058118:Transcription Factor 7-Like 2 Protein