Defective angiogenesis, endothelial migration, proliferation, and MAPK signaling in Rap1b-deficient mice

Abstract

Angiogenesis is the main mechanism of vascular remodeling during late development and, after birth, in wound healing. Perturbations of angiogenesis occur in cancer, diabetes, ischemia, and inflammation. While much progress has been made in identifying factors that control angiogenesis, the understanding of the precise molecular mechanisms involved is incomplete. Here we identify a small GTPase, Rap1b, as a positive regulator of angiogenesis. Rap1b-deficient mice had a decreased level of Matrigel plug and neonatal retinal neovascularization, and aortas isolated from Rap1b-deficient animals had a reduced microvessel sprouting response to 2 major physiological regulators of angiogenesis: vascular endothelial growth factor (VEGF) and basic fibroblasts growth factor (bFGF) , IntroductionAngiogenesis, sprouting of new capillaries from existing vascular beds, and vasculogenesis, de novo vessel formation via differentiation of endothelial precursor cells, angioblasts, provide 2 mechanisms through which blood vessels form. While vasculogenesis involves differentiation of embryonic progenitor cells and predominates in the early embryonic development, most vascular remodeling in late development and during physiological processes of organ growth and repair occurs via angiogenesis. This complex process is regulated by a controlled balance of proangiogenic and antiangiogenic factors and, when deregulated, contributes to multiple metastatic, ischemic, inflammatory, and immune disorders. 1 Vascular endothelial growth factors (VEGFs), in particular VEGF-A, are involved in the regulation of the processes required for angiogenesis: endothelial cell activation, proliferation, migration, and tubule formation. 2 The tyrosine kinase receptor VEGFR2 (flk-1/KDR) is the major receptor responsible for the biochemical effects of VEGF-A on cells and is indispensable for normal vascular development. 3 Activation of VEGFR2 leads to recruitment and activation of multiple signaling molecules. Among those are 2 MAP kinases: p42/44 ERK1/2 involved in regulation of endothelial proliferation and p38 MAPK, one of the critical modulators of actin cytoskeleton remodeling required for migration. 4 Targeted genetic deletion of either p38␣ or ERK2 is embryonic lethal, as each has been shown to be required for placental development and angiogenesis. [5][6][7] Signaling from VEGFR2 is bidirectionally regulated by integrins. 8,9 Rap1 is a small GTPase that becomes activated downstream from multiple surface receptors via guanine nucleotide exchange factors (GEFs) and regulates several basic cellular functions: adhesion, migration, polarity, differentiation, and growth. 10,11 Rap1 has been shown to regulate integrin activation, and specific molecular links between activation of Rap1 and activation of integrins have been proposed. 12 Rap1 has also been shown to activate MAP kinase pathway in several cell types. 13 Much of the research on Rap1 in endothelial cells has focused on its role in regulation of cadherin-based cell-cell junctions and vascular permeabi...

Novel Anti-Angiogenic Activity in Rubus coreanus Miquel Water Extract Suppresses VEGF-Induced Angiogenesis

“…The activation of ERK and p38 MAP kinase plays an important role in endothelial cell proliferation and migration (Rousseau et al, 1997;Chrzanowska-Wodnicka et al, 2008;Matsunaga et al, 2008). In addition, the results of the present study showed that RCME inhibited phosphorylation of VEGFR2, resulting in downregulation of ERK and p38 MAP kinase phosphorylation in response to VEGF in HUVECs (Fig.…”

“…In order to identify the downstream signaling pathways targeted by RCME, we next examined the phosphorylation of MAPK, one of the key signaling pathway components that drive endothelial cell proliferation, migration and tube formation (Rousseau et al, 1997;Takahashi et al, 1999;Huang et al, 2004;Chrzanowska et al, 2008). While treatment with RCME inhibited VEGF-dependent phosphorylation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and p38 in a dose-dependent manner, total ERK and p38 levels were not affected ( Figs.…”

Purinergic A2b Receptor Activation by Extracellular Cues Affects Positioning of the Centrosome and Nucleus and Causes Reduced Cell Migration

“…The A2b-Epac1-Rap1B Pathway in the Context of Migration of Cancer Cells-Our discovery of a critical involvement of Rap1B in the positioning of the centrosome and nucleus may explain previous observations that cells isolated from Rap1B-deficient mice display decreased migration (80), that Rap1B knockdown results in impaired cell migration of human endothelial cells (81), and that Rap1B suppression by miR-708 results in inhibition of ovarian cancer cell migration/invasion (83). However, some studies reported a correlation between hypoxia and cell motility in cancer cells, including enhanced metastatic potential (84,85).…”

“…Lung endothelial cells isolated from Rap1B-deficient mice display decreased migration in vitro (80). Rap1B knockdown by RNAi in endothelial cells and human umbilical vein endothelial cells results in the same phenotype (81, 82).…”

EphrinB2 Activation Enhances Vascular Repair Mechanisms and Reduces Brain Swelling After Mild Cerebral Ischemia

“…[24][25][26] Proliferation and migration of ECs has been shown to be an essential criterion for angiogenesis. [27][28][29] We demonstrate active EC proliferation that turns the ischemic hemisphere into a highly plastic vascular system with multiple angiogenic sprouts. The continued angiogenic sprouting results in an increased vessel density in both perilesion and lesion region.…”