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

Howard EW, Been LF, Lerner M, Brackett D, Lightfoot S, Bullen EC, Sanghera DK - BMC Genet. (2013)

Bottom Line: Prevalence of Wnt16a insertion did not differ among T2D cases (33%) and controls (32%).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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.

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.

Show MeSH

Related in: MedlinePlus

Gene expression study of TCF7L2 in the same 27 pancreatic tissues usedto determine the expression of Wnt16a by real-time PCR analysis.Figure 5A shows a significant elevationof TCF7L2 mRNA levels among CCCA insertion carriers and a very lowexpression of TCF7L2 mRNA was observed in non-carriers (p= 0.003).Figure 5B shows that within CCCAinsertion carriers, the expression of TCF7L2 mRNA in pancreas waselevated among diabetics compared to non-diabetic controls.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3675375&req=5

Figure 5: Gene expression study of TCF7L2 in the same 27 pancreatic tissues usedto determine the expression of Wnt16a by real-time PCR analysis.Figure 5A shows a significant elevationof TCF7L2 mRNA levels among CCCA insertion carriers and a very lowexpression of TCF7L2 mRNA was observed in non-carriers (p= 0.003).Figure 5B shows that within CCCAinsertion carriers, the expression of TCF7L2 mRNA in pancreas waselevated among diabetics compared to non-diabetic controls.

Mentions: The Wnt16a message, which is uniquely expressed in pancreas, includes an upstreamopen reading frame (uORF) that initiates 14 bp 5′ of the codingsequence AUG (Figure 3). Translation of this 5′UTR would terminate 140 bp later, presumably resulting in nonsense-mediateddecay (NMD) of the message, since two down-stream exon junction complexes wouldnot be disrupted during the pioneer round of translation [21]. The 4-base-pair insertion (CCCA) of the mutated Wnt16a message, onthe other hand, would result in the transition of the uORF to an in-framealternative translation initiation site. In this case, translation initiationfrom either the first or second AUG during the pioneer round of translationwould not trigger NMD. RT-PCR and qualitative gene expression studies wereperformed by quantifying mRNA expression of WNT16a and TCF7L2genes among carriers and non-carriers of Wnt16a. Of 27 participant donors ofhuman pancreatic tissue, nine were carriers of the insertion in WNT16a.As shown in Figure 4, our data revealed a ~3.2-foldincrease in the expression of WNT16a among insertion carriers compared tonon-carriers. The expression of WNT16a was consistently higher among insertioncarriers irrespective of disease status. Gene expression analysis ofTCF7L2 in the same pancreatic tissues revealed a significantelevation (p=0.003) of the amount of TCF7L2 mRNA among insertion carrierscompared to non-carriers (Figure 5A). In thestratified data by disease within CCCA insertion carriers, the expression ofTCF7L2 mRNA was higher in diabetic pancreatic tissues compared to non-diabeticpancreas, however, this increase was not statistically significant (p=0.155).(Figure 5B). Further stratification ofquantitative mRNA expression among the at-risk ‘T’ allelecarriers of TCF7L2 SNP (rs7903146) revealed that the CT+TT genotypesshowed an 8.7-fold increase in the expression of TCF7L2 compared to CC genotypesin Wnt16 a insertion carriers, while the non-insertion carriers showed the sameallelic trend at a significantly reduced magnitude (Figure 6).


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

Howard EW, Been LF, Lerner M, Brackett D, Lightfoot S, Bullen EC, Sanghera DK - BMC Genet. (2013)

Gene expression study of TCF7L2 in the same 27 pancreatic tissues usedto determine the expression of Wnt16a by real-time PCR analysis.Figure 5A shows a significant elevationof TCF7L2 mRNA levels among CCCA insertion carriers and a very lowexpression of TCF7L2 mRNA was observed in non-carriers (p= 0.003).Figure 5B shows that within CCCAinsertion carriers, the expression of TCF7L2 mRNA in pancreas waselevated among diabetics compared to non-diabetic controls.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3675375&req=5

Figure 5: Gene expression study of TCF7L2 in the same 27 pancreatic tissues usedto determine the expression of Wnt16a by real-time PCR analysis.Figure 5A shows a significant elevationof TCF7L2 mRNA levels among CCCA insertion carriers and a very lowexpression of TCF7L2 mRNA was observed in non-carriers (p= 0.003).Figure 5B shows that within CCCAinsertion carriers, the expression of TCF7L2 mRNA in pancreas waselevated among diabetics compared to non-diabetic controls.
Mentions: The Wnt16a message, which is uniquely expressed in pancreas, includes an upstreamopen reading frame (uORF) that initiates 14 bp 5′ of the codingsequence AUG (Figure 3). Translation of this 5′UTR would terminate 140 bp later, presumably resulting in nonsense-mediateddecay (NMD) of the message, since two down-stream exon junction complexes wouldnot be disrupted during the pioneer round of translation [21]. The 4-base-pair insertion (CCCA) of the mutated Wnt16a message, onthe other hand, would result in the transition of the uORF to an in-framealternative translation initiation site. In this case, translation initiationfrom either the first or second AUG during the pioneer round of translationwould not trigger NMD. RT-PCR and qualitative gene expression studies wereperformed by quantifying mRNA expression of WNT16a and TCF7L2genes among carriers and non-carriers of Wnt16a. Of 27 participant donors ofhuman pancreatic tissue, nine were carriers of the insertion in WNT16a.As shown in Figure 4, our data revealed a ~3.2-foldincrease in the expression of WNT16a among insertion carriers compared tonon-carriers. The expression of WNT16a was consistently higher among insertioncarriers irrespective of disease status. Gene expression analysis ofTCF7L2 in the same pancreatic tissues revealed a significantelevation (p=0.003) of the amount of TCF7L2 mRNA among insertion carrierscompared to non-carriers (Figure 5A). In thestratified data by disease within CCCA insertion carriers, the expression ofTCF7L2 mRNA was higher in diabetic pancreatic tissues compared to non-diabeticpancreas, however, this increase was not statistically significant (p=0.155).(Figure 5B). Further stratification ofquantitative mRNA expression among the at-risk ‘T’ allelecarriers of TCF7L2 SNP (rs7903146) revealed that the CT+TT genotypesshowed an 8.7-fold increase in the expression of TCF7L2 compared to CC genotypesin Wnt16 a insertion carriers, while the non-insertion carriers showed the sameallelic trend at a significantly reduced magnitude (Figure 6).

Bottom Line: Prevalence of Wnt16a insertion did not differ among T2D cases (33%) and controls (32%).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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.

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.

Show MeSH
Related in: MedlinePlus