The Role of RASGRP2 in Vascular Endothelial Cells-A Mini Review

RAS guanyl nucleotide-releasing proteins (RASGRPs) are important proteins that act as guanine nucleotide exchange factors, which activate small GTPases and function as molecular switches for intracellular signals. The RASGRP family is composed of RASGRP1-4 proteins and activates the small GTPases, RAS and RAP. Among them, RASGRP2 has different characteristics from other RASGRPs in that it targets small GTPases and its localizations are different. Many studies related to RASGRP2 have been reported in cells of the blood cell lineage. Furthermore, RASGRP2 has also been reported to be associated with Huntington's disease, tumors, and rheumatoid arthritis. In addition, we also recently reported RASGRP2 expression in vascular endothelial cells, and clarified the involvement of xenopus Rasgrp2 in the vasculogenesis process and multiple signaling pathways of RASGRP2 in human vascular endothelial cells with stable expression of RASGRP2. Therefore, this article outlines the existing knowledge of RASGRP2 and focuses on its expression and role in vascular endothelial cells, and suggests that RASGRP2 functions as a protective factor for maintaining healthy blood vessels.

RasGRP2 inhibits glyceraldehyde-derived toxic advanced glycation end-products from inducing permeability in vascular endothelial cells

Advanced glycation end-products (AGEs) are formed by the non-enzymatic reaction of sugars and proteins. Among the AGEs, glyceraldehyde-derived toxic AGEs (TAGE) are associated with various diseases, including diabetic complications such as diabetic retinopathy (DR). The risk of developing DR is strongly associated with poor glycemic control, which causes AGE accumulation and increases AGE-induced vascular permeability. We previously reported that Ras guanyl nucleotide releasing protein 2 (RasGRP2), which activates small G proteins, may play an essential role in the cell response to toxicity when exposed to various factors. However, it is not known whether RasGRP2 prevents the adverse effects of TAGE in vascular endothelial cells. This study observed that TAGE enhanced vascular permeability by disrupting adherens junctions and tight junctions via complex signaling, such as ROS and non-ROS pathways. In particular, RasGRP2 protected adherens junction disruption, thereby suppressing vascular hyper-permeability. These results indicate that RasGRP2 is an essential protective factor of vascular permeability and may help develop novel therapeutic strategies for AGE-induced DR.

The inhibition of Bax activation-induced apoptosis by RasGRP2 via R-Ras-PI3K-Akt signaling pathway in the endothelial cells

Apoptosis of endothelial cells is a very important event in various diseases and angiogenesis. We recently reported that ras guanyl nucleotide releasing protein 2 (RasGRP2), which is a guanine nucleotide exchange factor, was expressed in the human umbilical vein endothelial cells (HUVECs) and that Rap1 activation by its overexpression inhibited apoptosis by suppressing tumor necrosis factor-α induced-reactive oxygen species (ROS) production. However, other signaling pathways and roles of RasGRP2 not mediated via Rap1 are not well understood. Therefore, we compared the Mock (M) and the RasGRP2-stable overexpression (R) immortalized HUVECs using BAM7 and anisomycin, which are apoptosis inducers. BAM7 and anisomycin induced apoptosis without causing ROS production, and such apoptosis was significantly increased in M cells, but not in R cells. RasGRP2 suppressed BAM7- and anisomycin-induced apoptosis, but not via the Rap1 pathway as observed using Rap1 knockdown. Furthermore, RasGRP2 activated not only Rap1 but also R-Ras, and suppressed apoptosis by activating R-Ras-phosphoinositide 3-kinase (PI3K)-Akt signaling pathway. The phosphorylation of Akt by RasGRP2 inhibited Bax translocation by promoting translocation of hexokinase-2 (HK-2) from cytoplasm to mitochondria. Taken together, it was suggested that RasGRP2 suppresses the Bax activation-induced apoptosis by promoting HK-2 translocation to mitochondria via R-Ras-PI3K-Akt signaling pathway.

RASGRP2 Suppresses Apoptosis via Inhibition of ROS Production in Vascular Endothelial Cells

We have identified ras guanyl releasing protein 2 (rasgrp2) as a blood vessel related gene from Xenopus embryo. In addition, we reported that RASGRP2 is also expressed in human umbilical vein endothelial cells (HUVEC). It is known that RASGRP2 activates Ras-related protein 1 (Rap1). However, the function of RASGRP2 in human vascular endothelium remains unknown. Therefore, we performed functional analysis of RASGRP2 using immortalized HUVEC (TERT HUVEC). We established a stable RASGRP2 overexpressing cell line (TERT HUVEC R) and mock cell line (mock). Furthermore, we compared the activity of Rap1 and the generation of intracellular reactive oxygen species (ROS), which is related to cell death, in both cell lines. Significant increase in Rap1 activity was observed in the TERT HUVEC R compared to the mock. Furthermore, apoptosis by tumor necrosis factor-α (TNF-α) stimulation was significantly more reduced in the TERT HUVEC R than in the mock. In the mock, apoptosis induced by TNF-α stimulation was decreased by pretreatment with diphenyleneiodonium (DPI), which is an inhibitor of NADPH oxidase (NOX). However, in the TERT HUVEC R, apoptosis induced by TNF-α stimulation was not reduced after pretreatment of DPI. Furthermore, there was no reduction in ROS production in the TERT HUVEC R after DPI pretreatment. In addition, the difference in the degree of apoptosis induced by TNF-α stimulation in both cell lines was consistent with the difference in ROS production in the cell lines. From these results, it was suggested that RASGRP2 activates Rap1 and the activated Rap1 suppresses apoptosis via NOX inhibition.

In Vitro Induction of Xenopus Embryonic Organs Using Animal Cap Cells

The animal cap-the presumptive ectoderm of the blastula embryo-can differentiate into a variety of tissues belonging to the three germ layers following exposure to specific inducers. The "animal cap assay" was devised based on the pluripotency of presumptive ectodermal cells and enabled many important discoveries in the field of embryonic induction and cell differentiation. Using this system, investigators can test multiple factors in solution simultaneously to determine their inducing activities qualitatively, quantitatively, and synergistically. Furthermore, after dissociation and induction, reaggregated animal cap cells can be induced to form higher-order organs. This protocol details preoperative preparations, followed by the basic animal cap assay. Advanced protocols for the induction of kidney, pancreas, and heart are also described.

Molecular and cellular mechanisms of bone morphogenetic proteins and activins in the skin: potential benefits for wound healing

Bone morphogenetic proteins (BMPs) and activins are phylogenetically conserved proteins, belonging to the transforming growth factor-β superfamily, that signal through the phosphorylation of receptor-regulated Smad proteins, activating different cell responses. They are involved in various steps of skin morphogenesis and wound repair, as can be evidenced by the fact that their expression is increased in skin injuries. BMPs play not only a role in bone regeneration but are also involved in cartilage, tendon-like tissue and epithelial regeneration, maintain vascular integrity, capillary sprouting, proliferation/migration of endothelial cells and angiogenesis, promote neuron and dendrite formation, alter neuropeptide levels and are involved in immune response modulation, at least in animal models. On the other hand, activins are involved in wound repair through the regulation of skin and immune cell migration and differentiation, re-epithelialization and granulation tissue formation, and also promote the expression of collagens by fibroblasts and modulate scar formation. This review aims at enunciating the effects of BMPs and activins in the skin, namely in skin development, as well as in crucial phases of skin wound healing, such as inflammation, angiogenesis and repair, and will focus on the effects of these proteins on skin cells and their signaling pathways, exploring the potential therapeutic approach of the application of BMP-2, BMP-6 and activin A in chronic wounds, particularly diabetic foot ulcerations.

Ras guanyl nucleotide releasing protein 2 affects cell viability and cell-matrix adhesion in ECV304 endothelial cells

Ras guanyl nucleotide releasing proteins (RasGRPs) are guanine nucleotide exchange factors that activate Ras and Rap. We recently reported that xrasgrp2, which is a homolog of the human rasgrp2, plays a role in vasculogenesis and/or angiogenesis during early development of Xenopus embryos. However, the function of RasGRP2 in human vascular endothelium remains unknown. Therefore we aimed to analyze the function of human RasGRP2 in vascular endothelial cells. RasGRP2 overexpression did not increase Ras activation. However, it slightly increased Ras expression and increased proliferation in ECV304 cells. Furthermore, RasGRP2 overexpression increased Rap1 activation and cell-matrix adhesion in ECV304 cells. These data demonstrate that RasGRP2 increases cell viability and cell-matrix adhesion through increased Ras expression and Rap1 activation, respectively, in endothelial cells.

Identification of the gene regulatory region in human rasgrp2 gene in vascular endothelial cells

Ras guanyl nucleotide-releasing protein 2 (RASGRP2) is a calcium- and diacylglycerol-responsive guanine nucleotide exchange factor. Previously, we reported that XRASGRP2, a homolog of human RASGRP2, is expressed in the vascular region of the Xenopus embryo during embryogenesis. Here, we report the regulatory mechanisms of human rasgrp2 gene expression in vascular endothelial cells. Although three alternative splicing variants, differing in the first exon of 5'-untranslated region (5'-UTR), have been found for the human rasgrp2 gene, reverse transcription-polymerase chain reaction (RT-PCR) showed that the cDNA containing the distal first exon (D1E) was expressed only in human umbilical artery endothelial cells. We analyzed the 5'-flanking region of the human rasgrp2 gene by a luciferase assay, which revealed that not only a promoter but also silencer regions were present upstream of D1E, suggesting that rasgrp2 expression is controlled by a combination of transcriptional promotion and repression. Gel super shift assay demonstrated that OCT1/POU2F1 bound to the silencer region. These findings may help furthering our understanding of vasculogenesis and/or angiogenesis in vascular endothelial cells.

XRASGRP2 expression during early development of Xenopus embryos

Previously, we described the DNA microarray screening of vascular endothelial cells that were formed by treatment of aggregates prepared from Xenopus animal cap cells with activin and angiopoietin-2. One of the genes identified in this screening showed homology to human RASGRP2 which plays a role in the regulation of GTP-GDP exchange of the Ras and Rap proteins, and was named XRASGRP2. In the present study, we analyzed the expression pattern of xrasgrp2 during Xenopus embryogenesis. The xrasgrp2 mRNA was expressed after stage 24, as assessed by stage PCR analysis. Whole-mount in situ hybridization showed that xrasgrp2 mRNA was located in the vascular region of the embryo. Loss-of-function analysis revealed that the formation of blood and endothelial cells in the explants transplanted into Xenopus embryos was inhibited by antisense morpholino oligonucleotides that block xrasgrp2 translation. These results suggest that XRASGRP2 plays a role in angiogenesis in Xenopus embryos.