Chun, Chang Zoon

Vascular permeability factor/vascular endothelial growth factor A (VEGF) is a central regulator of angiogenesis and potently promotes vascular permeability. VEGF plays a key role in the pathologies of heart disease, stroke, and cancer. Therefore, understanding the molecular regulation of VEGF signaling is an important pursuit. Rho GTPase proteins play various roles in vasculogenesis and angiogenesis. While the functions of RhoA and RhoB in these processes have been well defined, little is known about the role of RhoC in VEGF-mediated signaling in endothelial cells and vascular development. Here, we describe how RhoC modulates VEGF signaling to regulate endothelial cell proliferation, migration and permeability. We found VEGF stimulation activates RhoC in human umbilical vein endothelial cells (HUVECs), which was completely blocked after VEGF receptor 2 (VEGFR-2) knockdown indicating that VEGF activates RhoC through VEGFR-2 signaling. Interestingly, RhoC knockdown delayed the degradation of VEGFR-2 compared to control siRNA treated HUVECs, thus implicating RhoC in VEGFR-2 trafficking. In light of our results suggesting VEGF activates RhoC through VEGFR-2, we sought to determine whether RhoC regulates vascular permeability through the VEGFR-2/phospholipase Cγ (PLCγ) /Ca 2+ /eNOS cascade. We found RhoC knockdown in VEGF-stimulated HUVECs significantly increased PLC-γ1 phosphorylation at tyrosine 783, promoted basal and VEGF-stimulated eNOS phophorylation at serine 1177, and increased calcium flux compared with control siRNA transfected HUVECs. Taken together, our findings suggest RhoC negatively regulates VEGF-induced vascular permeability. We confirmed this finding through a VEGF-inducible zebrafish model of vascular permeability by observing significantly greater vascular permeability in RhoC morpholino (MO)-injected zebrafish than control MO-injected zebrafish. Furthermore, we showed that RhoC promotes endothelial cell proliferation and negatively regulates endothelial cell migration. Our data suggests a scenario in which RhoC promotes proliferation by upregulating -catenin in a Wnt signaling-independent manner, which in turn, promotes Cyclin D1 expression and subsequently drives cell cycle progression.

Vasculogenesis and angiogenesis are controlled by vascular permeability factor/vascular endothelial growth factor A (VEGF). Dysregulation of these physiological processes contributes to the pathologies of heart disease, cancer and stroke. Rho GTPase proteins play an integral role in VEGF-mediated formation and maintenance of blood vessels. The regulatory functions of RhoA and RhoB in vasculogenesis and angiogenesis are well defined, whereas the purpose of RhoC remains poorly understood. Here, we describe how RhoC promotes vascular homeostasis by modulating endothelial cell migration, proliferation, and permeability. RhoC stimulates proliferation of human umbilical vein endothelial cells (HUVEC) by stabilizing nuclear β-catenin, which promotes transcription of cyclin D1 and subsequently drives cell cycle progression. RhoC negatively regulates endothelial cell migration through MAPK and downstream MLC-2 signaling and decreases vascular permeability through downregulation of the phospholipase Cγ (PLCγ)/Ca2+/eNOS cascade in HUVEC. Using a VEGF-inducible zebrafish (Danio rerio) model, we observed significantly less vascular permeability in RhoC morpholino (MO)-injected zebrafish than control MO-injected zebrafish. Taken together, our findings suggest RhoC is a key regulator of vascular homeostasis in endothelial cells.

AbstractEndothelial cell–specific chemotaxis receptor (ECSCR) is a cell surface protein expressed by blood endothelial cells with roles in endothelial cell migration and signal transduction. We investigated the function of ecscr in the development of the zebrafish vasculature. Zebrafish ecscr is expressed in angioblasts and in axial vessels during angioblast migration and vasculogenesis. Morpholino-directed ecscr knockdown resulted in defective angioblast migration in the posterior lateral plate mesoderm, a process known to depend on vascular endothelial-derived growth factor (VEGF). In cultured cells, transfected ECSCR localized to actin-rich membrane protrusions, colocalizing with kinase insert domain protein receptor (KDR)/VEGF receptor 2 in these regions. ECSCR-silenced cells show reduced VEGF-induced phosphorylation of KDR but not of FMS-like tyrosine kinase 1 (FLT1)/VEGF receptor 1. Finally, chemical inhibition of VEGF receptor activity in zebrafish resulted in angioblast deficiencies that partially overlap with those seen in ecscr morphants. We propose that ecscr promotes migration of zebrafish angioblasts by enhancing endothelial kdr sensitivity to VEGF.

AbstractIn vertebrates, molecular mechanisms dictate angioblasts' migration and subsequent differentiation into arteries and veins. In this study, we used a microarray screen to identify a novel member of the sucrose nonfermenting related kinase (snrk-1) family of serine/threonine kinases expressed specifically in the embryonic zebrafish vasculature and investigated its function in vivo. Using gain- and loss-of-function studies in vivo, we show that Snrk-1 plays an essential role in the migration, maintenance, and differentiation of angioblasts. The kinase function of Snrk-1 is critical for migration and maintenance, but not for the differentiation of angioblasts. In vitro, snrk-1 knockdown endothelial cells show only defects in migration. The snrk-1 gene acts downstream or parallel to notch and upstream of gridlock during artery-vein specification, and the human gene compensates for zebrafish snrk-1 knockdown, suggesting evolutionary conservation of function.