Poster 1
Presenter: Sushant Bhatnagar
Wednesday, 3:00 – 5:00pm
Sushant Bhatnagar1, Lindsay R. Schneider1, Alex Hebert2, Muffadal Soni1, Mark Keller1, Joshua J. Coon2, Alan D. Attie1 Department of Biochemistry1, Department of Chemistry2, University of Wisconsin-Madison, Madison, WI, USA
We previously mapped a type 2 diabetes (T2D) locus on chromosome 16 (Chr 16) in an F2 intercross between the diabetes susceptible BTBR T (+) tf (BTBR) Lepob/ob and diabetes resistant C57BL/6 (B6) Lepob/ob mouse strains. Using a panel of sub-congenic mice, T2D locus was narrowed to a 1.6 Mb region. The congenic mice containing 1.6 Mb fragment of the BTBR Chr 16 into lean B6 mice (B6.16BT36–38) were hyperglycemic and hypoinsulinemic, and islets from these mice were defective in insulin secretion compared to islets from B6 mice. Within this region, we identified that a non-synonymous coding single nucleotide polymorphism (SNP) in the syntaxin-binding protein 5-like (Stxbp5l or tomosyn-2) was associated with the hyperglycemia and hypoinsulinemia in the B6.16BT36–38 mice. Our results showed that tomosyn-2 is a negative regulator of insulin secretion and that the SNP in tomosyn-2 gene affects its proteasomal degradation. Tomosyn-2 is relatively uncharacterized protein and contains a syntaxin-binding domain; syntaxin is a member of the SNARE complex that regulates insulin secretion. Preliminary results show that tomosyn-2 is phosphorylated and degraded by glucose-, cAMP-, and phorbol esters-activated signaling pathways in pancreatic β-cell line. Furthermore, by using mass spectrometry and molecular biology approaches we have identified an E3 ligase, Hrd1, which binds and regulates the abundance of tomosyn-2. These results led us to hypothesize that phosphorylation of tomosyn-2 regulates insulin secretion by modulating its protein abundance. Herein, we propose that alterations in tomosyn-2 phosphorylation will lead to inappropriate insulin secretion from the beta-cells. This will result in increased susceptibility towards T2D and can also lead to potentially life threatening hypoglycemia during fasting.