Genotype and tissue-specific effects on alternative splicing of the transcription factor 7-like 2 gene in humans.
BACKGROUND
Noncoding single-nucleotide polymorphisms (SNPs) within the TCF7L2 gene are confirmed risk factors for type 2 diabetes, but the mechanism by which they increase risk is unknown.


OBJECTIVE
We hypothesized that associated SNPs alter TCF7L2 splicing and that splice forms have altered biological roles.


METHODS
Splice forms and 5' and 3' untranslated regions were characterized in sc adipose, muscle, liver, HepG2 cells, pancreas, and islet. Isoform-specific transcript levels were quantified in sc adipose. Alternative splice forms were characterized in HepG2 liver cells under glucose and insulin conditions and in SGBS cells with differentiation. Major isoforms were characterized by transfection.


METHODS
The study was conducted at an ambulatory general clinical research center.


METHODS
PATIENTS included 78 healthy, nondiabetic study subjects characterized for insulin sensitivity and secretion.


RESULTS
We identified 32 alternatively spliced transcripts and multiple-length 3' untranslated region transcripts in adipose, muscle, islet, and pancreas. Alternative exons 3a, 12, 13, and 13a were observed in all tissues, whereas exon 13b was islet specific. Transcripts retaining exons 13 and 13a but not total TCF7L2 transcripts were significantly correlated with both obesity measures (P < 0.01) and rs7903146 genotype (P < 0.026) in sc adipose. Insulin (5-10 nm) suppressed all TCF7L2 isoforms in SGBS cells but suppressed exon 13a-containing isoforms most significantly (P < 0.001). The isoform distribution differed throughout SGBS cell differentiation. Isoforms with predicted early stop codons yielded stable proteins of the predicted size, bound beta-catenin, and targeted correctly to the nucleus.


CONCLUSIONS
Intronic TCF7L2 variants may regulate alternative transcript isoforms, which in turn may have distinct physiologic roles.
Mondal
Ashis K
AK
or Swapan K. Das, Section on Endocrinology and Metabolism, Department of Internal Medicine, Wake Forest University Health Sciences, Medical Center Boulevard, Winston-Salem, North Carolina 27157, USA.
Das
Swapan K
SK
Baldini
Giulia
G
Chu
Winston S
WS
Sharma
Neeraj K
NK
Hackney
Oksana G
OG
Zhao
Jianhua
J
Grant
Struan F A
SF
Elbein
Steven C
SC
D000273:Adipose Tissue / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D017398:Alternative Splicing / Q000235:genetics*; D000704:Analysis of Variance; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism; D005091:Exons; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D014644:Genetic Variation; D005838:Genotype; D056945:Hep G2 Cells; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism; D009928:Organ Specificity; D010179:Pancreas / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051820:TCF Transcription Factors / Q000235:genetics* / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein
D007328:Insulin; D020033:Protein Isoforms; D012333:RNA, Messenger; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D058118:Transcription Factor 7-Like 2 Protein