VEGF regulates the mobilization of VEGFR2/KDR from an intracellular endothelial storage compartment

Abstract

Endothelial cells respond to vascular endothelial growth factor (VEGF) to produce new blood vessels. This process of angiogenesis makes a critical contribution during embryogenesis and also in the response to ischemia in adult tissues. We have studied the intracellular trafficking of the major VEGF receptor KDR (VEGFR2). Unlike other related growth factor receptors, we find that a significant proportion of KDR is held in an endosomal storage pool within endothelial cells. We find that KDR can be delivered to the plasma membrane from this intracellular pool and that VEGF stimulates this recycling to the cell surface. KDR recycling appears to be distinct from the previously characterized Rab4-and Rab11-dependent pathways, but, instead, KDR ؉ recycling vesicles contain Src tyrosine kinase and VEGFstimulated recycling requires Src activa- IntroductionAngiogenesis is the fundamental physiologic process by which new blood vessels are generated from preexisting vasculature. It plays a crucial role in embryogenesis, where it is required for elaboration of the vasculature from the primary vascular plexus. In normal adult physiology, angiogenesis is significant in a relatively limited number of processes-primarily in the formation of endometrial vessels in the uterus and development of the corpus luteum during the ovulation cycle. 1 Angiogenesis becomes more widely important to adult physiology through its critical involvement in a number of pathologic conditions. Active angiogenesis makes a positive contribution to the woundhealing process and also in the response to tissue ischemia-hypoxic tissues generate proangiogenic signals that stimulate the formation of new vessels and so improve perfusion. 2 Angiogenesis makes an unwanted contribution to the growth of solid tumors, with cancer cells secreting proangiogenic factors to provide a blood supply for the growing mass. 3 Deregulated angiogenesis is an underlying cause of proliferative diabetic retinopathy, a major vascular complication of both type I and type II diabetes, 4 and also contributes to other disease states such as age-related macular degeneration, rheumatoid arthritis, and psoriasis. 5,6 Understanding of the regulatory mechanisms of angiogenesis is hence seen not only as a fundamental problem in human biology but also as an important goal in medical research.Angiogenesis is controlled by a wide range of positive and negative signals. Vascular endothelial growth factor (VEGF) is the most critical and potent of the proangiogenic regulators 7-9 and is secreted by tissues in response to hypoxia or inflammation. 9 VEGF binds to VEGF receptors (VEGFRs) on the surface of endothelial cells, triggering a cascading series of signaling pathways that stimulate endothelial cell sprouting, migration, tube formation, proliferation, and survival. 10 There are 3 human members of the VEGFR family: VEGFR1/Flt-1, VEGFR2/Flk-1/KDR, and VEGFR3/Flt-4. 11 These proteins are members of the larger family of receptor tyrosine kinases (RTKs), which includes the plateletderived growth f...

Phosphorylation of Tyrosine 801 of Vascular Endothelial Growth Factor Receptor-2 Is Necessary for Akt-dependent Endothelial Nitric-oxide Synthase Activation and Nitric Oxide Release from Endothelial Cells

“…VEGF stimulation of BAEC for 5 min induced a marked increase in the fluorescence signal, revealing a punctate distribution of the signal. This intracellular phosphorylation of tyrosine 801 of the VEGFR-2 is in line with the recent reports of an important contribution of the intracellular endosomal compartment in VEGFR-2 signaling (45,46). The Tyr 801 phosphorylation staining is very similar to Tyr 1175 phosphorylation recently reported by Lampugnani et al (46).…”

Aberrant association between vascular endothelial growth factor receptor-2 and VE-cadherin in response to vascular endothelial growth factor-a in Shb-deficient lung endothelial cells

“…2). In addition there was co-localization of these in the perinuclear region corresponding to the perinuclear recycling compartment [16]. VEGF-A reduced the co-localization of VE-cadherin/VEGFR-2 in the junctions of the wildtype cells (Fig.…”

“…Whereas VEGFR-2 recycles to a large extent to the cell surface [16] the fate of VEcadherin is less well described. Our previously reported in vivo observations in cremaster venules suggest that VE-cadherin dissociates from junctions to other cellular compartments in response to VEGF-A [11].…”

Transmigration at the borders

“…The regulation of trafficking kinetics of constitutive recycling transmembrane proteins seems to be a general mechanism to control their surface levels both in time and space in order to cope with changes in cellular requirements without need for protein synthesis. 5,6 One interesting hypothesis of the significance of PECAM targeted recycling provided by Mamdouh et al is that this mechanism might bring quickly unligated PECAM to endothelial borders for the interaction and guidance of leukocyte to the junction.…”