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.
J Clin Endocrinol Metab. 2010 Mar;95(3):1450-7. doi: 10.1210/jc.2009-2064. Epub 2010 Jan 22.
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.
We hypothesized that associated SNPs alter TCF7L2 splicing and that splice forms have altered biological roles.
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.
The study was conducted at an ambulatory general clinical research center.
PATIENTS included 78 healthy, nondiabetic study subjects characterized for insulin sensitivity and secretion.
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.
Intronic TCF7L2 variants may regulate alternative transcript isoforms, which in turn may have distinct physiologic roles.
TCF7L2 基因中的非编码单核苷酸多态性（SNPs）已被证实是 2 型糖尿病的风险因素，但它们增加风险的机制尚不清楚。
我们假设相关 SNPs 改变了 TCF7L2 的剪接，并且剪接形式具有改变的生物学作用。
在皮下脂肪、肌肉、肝脏、HepG2 细胞、胰腺和胰岛中对剪接形式和 5'和 3'非翻译区进行了特征描述。在皮下脂肪中定量了异构体特异性转录本水平。在葡萄糖和胰岛素条件下以及在分化的 SGBS 细胞中研究了 HepG2 肝细胞中的替代剪接形式。主要异构体通过转染进行了特征描述。
该研究在一个门诊普通临床研究中心进行。
患者包括 78 名健康、非糖尿病的研究对象，这些研究对象的胰岛素敏感性和分泌情况进行了特征描述。
我们在脂肪、肌肉、胰岛和胰腺中鉴定出 32 种剪接转录本和多种长度的 3'非翻译区转录本。所有组织中均观察到外显子 3a、12、13 和 13a 的替代，而外显子 13b 是胰岛特异性的。保留外显子 13 和 13a 但不保留总 TCF7L2 转录本的转录本与皮下脂肪中的肥胖指标（P < 0.01）和 rs7903146 基因型（P < 0.026）均呈显著相关。胰岛素（5-10nm）抑制了 SGBS 细胞中的所有 TCF7L2 异构体，但抑制含有外显子 13a 的异构体最为显著（P < 0.001）。随着 SGBS 细胞分化，异构体的分布也不同。具有预测的早期终止密码子的异构体产生预测大小的稳定蛋白，结合 beta-catenin，并正确靶向细胞核。
TCF7L2 基因内含子中的变异可能调节了不同的转录本异构体，而这些异构体可能具有不同的生理作用。
