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

Abstract

Class II α-isoform of phosphatidylinositol 3-kinases (PI3K-C2α) is localized in endosomes, the trans-Golgi network and clathrin-coated vesicles, however, its functional role is little understood. Global or endothelial cell (EC)-specific targeted disruption of PI3K-C2α resulted in embryonic lethality due to defects in sprouting angiogenesis and vascular maturation. PI3K-C2α knockdown in ECs induced decreased phospatidylinositol 3-phosphate-enriched endosomes, impaired endosomal trafficking, and defective delivery of VE-cadherin to EC junctions and its assembly. PI3K-C2α knockdown also impeded cell signaling including vascular endothelial growth factor receptor internalization and endosomal RhoA activation. These together led to defective EC migration, proliferation, tube formation and barrier integrity. Endothelial PI3K-C2α deletion suppressed post-ischemic and tumor angiogenesis, and diminished vascular barrier function, with greatly augmented susceptibility to anaphylaxis and a higher incidence of dissecting aortic aneurysm formation in response to angiotensin II infusion. Thus, PI3K-C2α plays a crucial role in vascular formation and barrier integrity, and represents a new therapeutic target for vascular diseases. 3Formation of the vascular network by vasculogenesis and angiogenesis is essential for embryonic development, repair and remodeling of tissues in adults, as well as tumor growth. The angiogenic response to vascular endothelial growth factor (VEGF) and other factors begins with vascular leakage and dissolution of the subendothelial basement membrane, followed by proliferation and migration of vascular EC 1,2 . Then, formation of the intercellular junctions results in initial sprouts from existing vessels. The newly formed endothelial tubes are associated with mural cells, i.e. smooth muscle cells (SMC) and pericytes, thus becoming mature and stabilized 3 . Tightness of the intercellular junctions, particularly adherens junctions composed of VE-cadherin, controls vascular permeability 4,5 . Quiescent, stabilized vasculature with intact barrier integrity dominates in the healthy condition. In contrast, in pathological conditions, such as tumors, the vasculature is generally inmaturate and leaky. In the case of vascular insult such as excessive angiotensin II (Ang II) activity, increased vascular permeability is asssociated with leukocyte infiltration in the vascular wall and vascular disruption 6,7 . Therefore, stabilization of the vasculature and maintenance of vascular integrity is essential for vascular and tissue homeostasis 8,9 .PI3Ks are an enzyme family that phosphorylates membrane inositol lipids at the 3' position of the inositol ring. The lipid products of PI3Ks serve as important intracellular messengers by interacting with effector proteins, which include protein kinases, guanine nucleotide exchangers for G proteins, and actin cytoskeleton-regulating proteins. Through these actions, PI3Ks regulate a diverse array of cellular processes 10-12 .PI3Ks comprise three classes. Class I PI...

Classes of phosphoinositide 3-kinases at a glance

“…Class II PI3K functions have been mostly (although controversially) attributed to PtdIns(3)P, which has roles in either cell signaling or intracellular membrane trafficking. Growing evidence suggests that these two mechanisms could be interrelated at the level of 'endosomal signaling' (Yoshioka et al, 2012;Biswas et al, 2013), or endosome platforms for the formation of specific signal transduction complexes and responses (Platta and Stenmark, 2011). With regard to cell signaling roles, PI3KC2-induced PtdIns(3)P appears to mediate immune cell K + channel activity (in the case of PI3KC2b), growth factor receptor responses, and activation of Rho GTPases in cell contraction and migration (in the cases of PI3KC2a and -b) (Bridges et al, 2012;Falasca and Maffucci, 2012;Yoshioka et al, 2012), whereas PI3KC2a-mediated PtdIns(3,4)P 2 activity has been associated with insulininduced Akt stimulation (Leibiger et al, 2010).…”

The role of the PI3K/AKT/mTOR pathway in brain tumor metastasis

“…[23,24] The important role of the PAM pathway in angiogenesis has been confirmed in various malignancies where inhibition of pan-PI3K by LY294002 and downregulation of p110α (or recently, PI3KC2α) were shown to block tumor vascularization. [15,22,25] In myeloid cells, PI3Kϒ was reported to be involved in the activation of integrin α4β1, leading to myeloid cell invasion into tumors and, in turn, to tumor angiogenesis. [26] In GBM, the most aggressive glioma subtype, the PAM pathway also plays a crucial role in the induction of invasion, angiogenesis and the expression of VEGF in cells.…”

“…The implications of aberrant PAM signaling in angiogenesis, epithelial to mesenchymal transition (EMT) and immune response modulation is currently under intense investigation. [13][14][15] Components of the PAM pathway are therefore being considered as potential drug targets [ Table 1] to inhibit the often fatal events of metastasis and cell invasion. [16][17][18] …”

cAMP-dependent protein kinase A (PKA) regulates angiogenesis by modulating tip cell behavior in a Notch-independent manner

“…One of the major mechanisms to translate such extracellular inputs into a cellular response is protein and lipid phosphorylation. However, specific roles for regulation of phosphorylation during angiogenesis have been assigned to only a few kinases and phosphatases (Deng et al, 2013;Nakayama et al, 2013;Serra et al, 2015;Yoshioka et al, 2012).…”