ABSTRACT
In contrast to the class I phosphoinositide 3-kinases (PI3Ks), the organismal roles of the kinase activity of the class II PI3Ks are less clear. Here, we report that class II PI3K-C2ß kinase-dead mice are viable and healthy but display an unanticipated enhanced insulin sensitivity and glucose tolerance, as well as protection against high-fat-diet-induced liver steatosis. Despite having a broad tissue distribution, systemic PI3K-C2ß inhibition selectively enhances insulin signaling only in metabolic tissues. In a primary hepatocyte model, basal PI3P lipid levels are reduced by 60% upon PI3K-C2ß inhibition. This results in an expansion of the very early APPL1-positive endosomal compartment and altered insulin receptor trafficking, correlating with an amplification of insulin-induced, class I PI3K-dependent Akt signaling, without impacting MAPK activity. These data reveal PI3K-C2ß as a critical regulator of endosomal trafficking, specifically in insulin signaling, and identify PI3K-C2ß as a potential drug target for insulin sensitization.
Subject(s)
Class II Phosphatidylinositol 3-Kinases/metabolism , Insulin/metabolism , Adaptor Proteins, Signal Transducing/metabolism , Animals , Autophagy , Blood Glucose/analysis , Cells, Cultured , Class II Phosphatidylinositol 3-Kinases/genetics , Diet, High-Fat , Endosomes/metabolism , Fatty Liver/metabolism , Fatty Liver/pathology , Gene Knock-In Techniques , Hepatocytes/cytology , Hepatocytes/metabolism , Insulin/blood , Liver/pathology , Mice , Mice, Inbred C57BL , Mitogen-Activated Protein Kinases/metabolism , Phosphorylation , Proto-Oncogene Proteins c-akt/metabolism , Signal TransductionABSTRACT
The PX domain, which until recently was an orphan domain, has emerged as the latest member of the phosphoinositide-binding module superfamily. Structural studies have revealed that it has a novel fold and identified key residues that interact with the bound phosphoinositide, enabling some prediction of phosphoinositide-binding specificity. Specificity for PtdIns(3)P appears to be the most common, and several proteins containing PX domains localise to PtdIns(3)P-rich endosomal and vacuolar structures through their PX domains: these include the yeast t-SNARE Vam7p, mammalian sorting nexins (involved in membrane trafficking events) and the Ser/Thr kinase CISK, which is implicated in cell survival. Additionally, phosphoinositide binding to the PX domains of p40(phox) and p47(phox) appears to play a critical role in the active assembly of the neutrophil oxidase complex.
