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...

These results suggest that chronic activation of SPHK1-S1P signalling results in both pathological cardiac remodelling through ROS mediated by S1P3 and favourable cardioprotective effects.

Sphingosine-1-phosphate (S1P) has been implicated in tumor angiogenesis by acting through the G i -coupled chemotactic receptor S1P 1 . Here, we report that the distinct receptor S1P 2 is responsible for mediating the G 12/13 /Rho-dependent inhibitory effects of S1P on Akt, Rac, and cell migration, thereby negatively regulating tumor angiogenesis and tumor growth. By using S1P 2 LacZ/+ mice, we found that S1P 2 was expressed in both tumor and normal blood vessels in many organs, in both endothelial cells (EC) and vascular smooth muscle cells, as well as in tumor-associated, CD11b-positive bone marrow-derived cells (BMDC). Lewis lung carcinoma or B16 melanoma cells implanted in S1P 2 -deficient (S1P 2 −/− ) mice displayed accelerated tumor growth and angiogenesis with enhanced association of vascular smooth muscle cells and pericytes. S1P 2 −/− ECs exhibited enhanced Rac activity, Akt phosphorylation, cell migration, proliferation, and tube formation in vitro. Coinjection of S1P 2 −/− ECs and tumor cells into wild-type mice also produced a relative enhancement of tumor growth and angiogenesis in vivo. S1P 2 −/− mice were also more efficient at recruiting CD11b-positive BMDCs into tumors compared with wild-type siblings. Bone marrow chimera experiments revealed that S1P 2 acted in BMDCs to promote tumor growth and angiogenesis. Our results indicate that, in contrast to endothelial S1P 1 , which stimulates tumor angiogenesis, S1P 2 on ECs and BMDCs mediates a potent inhibition of tumor angiogenesis, suggesting a novel therapeutic tactic for anticancer treatment.Cancer Res; 70(2); 772-81. ©2010 AACR.