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Open Access Research article

Carriers of a novel frame-shift insertion in WNT16a possess elevated pancreatic expression of TCF7L2

Eric W Howard1, Latonya F Been2, Megan Lerner3, Daniel Brackett4, Stan Lightfoot3, Elizabeth C Bullen1 and Dharambir K Sanghera2*

Author Affiliations

1 Department of Cell Biology, College of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA

2 Department of Pediatrics, College of Medicine, University of Oklahoma Health Sciences Center, 940 Stanton L. Young Blvd., Rm 317 BMSB, Oklahoma City, OK, 73104, USA

3 Department of Surgery, College of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA

4 Veteran Affairs, VA Medical Center, Oklahoma City, OK, USA

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BMC Genetics 2013, 14:28  doi:10.1186/1471-2156-14-28

Published: 23 April 2013

Abstract

Background

The discovery of TCF7L2 as a global type 2 diabetes (T2D) gene has sparked investigations to explore the clinical utility of its variants for guiding the development of new diagnostic and therapeutic strategies. However, interpreting the resulting associations into function still remains unclear. Canonical Wnt signaling regulates β-catenin and its binding with TCF7L2, which in turn is critical for the production of glucagon-like peptide-1 (GLP-1). This study examines the role of a novel frame-shift insertion discovered in a conserved region of WNT16a, and it is proposed that this mutation affects T2D susceptibility in conjunction with gene variants in TCF7L2.

Results

Our results predicted that the insertion would convert the upstream open reading frame in the Wnt16a mRNA to an alternative, in-frame translation initiation site, resulting in the prevention of nonsense-mediated decay, leading to a consequent stabilization of the mutated WNT16a message. To examine the role of Wnt16a in the Wnt signaling pathway, DNA and serum samples from 2,034 individuals (48% with T2D) from the Sikh Diabetes Study were used in this investigation. Prevalence of Wnt16a insertion did not differ among T2D cases (33%) and controls (32%). However, there was a 3.2 fold increase in Wnt16a mRNA levels in pancreatic tissues from the insertion carriers and a significant increase (70%, p < 0.0001) in luciferase activity in the constructs carrying the insertion. The expression of TCF7L2 mRNA in pancreas was also elevated (~23-fold) among the insertion carriers (p=0.003).

Conclusions

Our results suggest synergistic effects of WNT16a insertion and the at-risk ‘T’ allele of TCF7L2 (rs7903146) for elevating the expression of TCF7L2 in human pancreas which may affect the regulation of downstream target genes involved in the development of T2D through Wnt/β-catenin/TCF7L2 signaling pathway. However, further studies would be needed to mechanistically link the two definitively.

Keywords:
β-cat /TCF7L2 signaling; Wnt16a; Exome sequencing; Insertion polymorphism; TCF7L2 gene variants; Gene expression; Pancreatic β-cells; Type 2 diabetes