A Drosophila model of insulin resistance associated with the human Trib3 Q/R polymorphism

Abstract

Members of the Tribbles family of proteins are conserved pseudokinases with diverse roles in cell growth and proliferation. Both Drosophila Tribbles (Trbl) and vertebrate Trib3 proteins bind to Akt kinase to block its phosphorylation-activation and reduce downstream insulin-stimulated anabolism. A single nucleotide polymorphism (SNP) variant in human Trib3, which results in a glutamine (Q) to arginine (R) missense mutation in a conserved motif at position 84, confers stronger Akt binding resulting in reduced Akt phosphorylation and is associated with a predisposition to Type II diabetes, cardiovascular disease, diabetic nephropathy, chronic kidney disease and leukemogenesis. Here we used a Drosophila model to understand the importance of the conserved R residue in several Trbl functions. In the fly fat body, misexpression of a site-directed Q mutation at position R141 resulted in weakened binding to dAkt, leading to increased levels of phospho-dAkt, increased cell and tissue size and increases in levels of stored glycogen and triglycerides. Consistent with the functional conservation of this arginine in modulating Akt activity, mouse Trib3R84 misexpressed in the fly fat body blocked dAkt phosphorylation with a strength similar to wild type (WT) Trbl. Limited mutational analysis shows that the R141 site dictates the strength of Akt binding but does not affect other Trbl-dependent developmental processes, suggesting a specificity that may serve as drug target for metabolic diseases.