The Role of Phosphoinositide 3-Kinase C2α in Insulin Signaling

Abstract

The members of the class II phosphoinositide 3-kinase (PI3K) family can be activated by several stimuli, indicating that these enzymes can regulate many intracellular processes. Nevertheless, to date, there has been no definitive identification of their in vivo product, their mechanism(s) of activation, or their precise intracellular roles. By metabolic labeling, we here identify phosphatidylinositol 3-phosphate as the sole in vivo product of the insulin-dependent activation of PI3K-C2␣, confirming the emerging role of such a phosphoinositide in signaling. We demonstrate that activation of PI3K-C2␣ involves its recruitment to the plasma membrane and that activation is mediated by the GTPase TC10. This is the first report showing a membrane targeting-mediated mechanism of activation for PI3K-C2␣ and that a small GTP-binding protein can activate a class II PI3K isoform. We also demonstrate that PI3K-C2␣ contributes to maximal insulin-induced translocation of the glucose transporter GLUT4 to the plasma membrane and subsequent glucose uptake, definitely assessing the role of this enzyme in insulin signaling.

Endothelial PI3K-C2α, a class II PI3K, has an essential role in angiogenesis and vascular barrier function

“…Consistent with this, C2α was detected in a granular pattern in HUVEC with enrichment in the perinuclear region, and partially co-localized with markers of clathrin-coated vesicles, TGN and early endosomes ( Supplementary Fig. 14a-c) 16,18,22 . GFP-C2α also substantially overlapped with mRFP-2×FYVE ( Supplementary Fig.…”

“…The actions of C2α and class I PI3Ks in EC are distinct in that, different from C2α, class I PI3Ks exert a great impact on Akt stimulation and cell proliferation and are not involved in vesicular trafficking including VE-cadherin transfer or VE-cadherin assembly at the cell-cell junction [10][11][12][13] . Therefore, these observations reveal novel biological activities of C2α and underscore broader roles for PI3K family members in vascular physiology and pathophysiology.In contrast to class I PI3Ks that generate PtdIns(3,4,5)P 3 , the major product of class II and III PI3Ks is PtdIns(3)P, which is mainly accumulated in endosomes [16][17][18][20][21][22][23][24][25] .Consistent with this, C2α in EC was localized in endosomes and TGN, which are organelles responsible for processing, sorting and packaging proteins into distinct carriers for transport to their final destinations. Another class II PI3K-C2β and class III Vps34 are also localized primarily in the clathrin-coated or endocytic compartment 38,39 .…”

“…In contrast to class I and III, the physiological functions of class II PI3Ks are little understood. Class II PI3Ks comprise three members, PI3K-C2α (C2α), PI3K-C2β (C2β) and PI3K-C2γ (C2γ), and mainly produce PtdIns(3)P in vivo 16,17 . Among the three class II PI3Ks, C2α is distinct from C2β, C2γ and other PI3K 4 members in that it has unique structures including a clathrin-binding site in the Nterminal stretch and relative resistance to PI3K inhibitors 16,18 .…”

“…Class II PI3Ks comprise three members, PI3K-C2α (C2α), PI3K-C2β (C2β) and PI3K-C2γ (C2γ), and mainly produce PtdIns(3)P in vivo 16,17 . Among the three class II PI3Ks, C2α is distinct from C2β, C2γ and other PI3K 4 members in that it has unique structures including a clathrin-binding site in the Nterminal stretch and relative resistance to PI3K inhibitors 16,18 . C2α is expressed in selected cell populations including epithelium, vascular endothelium, and smooth muscle 19,20 .…”

Structural Basis for Interactions of thePhytophthora sojaeRxLR Effector Avh5 with Phosphatidylinositol 3-Phosphate and for Host Cell Entry

“…In animal cells, PtdIns(3)P also localizes to early endosomes, where it is required for protein trafficking. More recently, it has been reported that PtdIns(3)P associates with the plasma cell membrane during responses to insulin (123) and that plasma membrane-associated PtdIns(3)P is required for both glucose transporter 4 protein translocation to the plasma membrane (123) and neurosecretory granule release (124). PtdIns(3)P is generally found on the cytoplasmic leaflet of internal membranes.…”