Abstract
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.
Highlights
Vascular endothelial cells occur in the monolayer on the inside of blood vessels and act as a barrier to regulate the migration of blood components to the vessel wall
Anisomycin is a protein synthesis inhibitor, and is known to activate Bax by phosphorylating jun N-terminal kinase (JNK) and Bim and induce apoptosis[30]. Both compounds were found to cause apoptosis without affecting reactive oxygen species (ROS) production in the TERT human umbilical vein endothelial cells (HUVECs) (Fig. 1, S3a,b) and similar results were obtained in the HUVECs
These compounds were suitable for analyzing the novel mechanism of ras guanyl nucleotide releasing protein 2 (RasGRP2), and we showed that RasGRP2 completely suppressed the induction of apoptosis by BAM7 and anisomycin (Fig. 1c)
Summary
Vascular endothelial cells occur in the monolayer on the inside of blood vessels and act as a barrier to regulate the migration of blood components to the vessel wall. We showed that RasGRP2 is expressed in the human vascular endothelial cells, including the human umbilical vein endothelial cells (HUVECs)[26], and that Rap[1], activated by RasGRP2, suppresses apoptosis by suppressing reactive oxygen species (ROS) production via NADPH oxidase (NOX) inhibition in the endothelial cells[27]. These results suggested that RasGRP2 in the endothelial cells acts as a defense factor against apoptosis to maintain blood vessels. We performed further analysis of apoptosis-suppressing mechanism of RasGRP2 and discovered the R-Ras signaling pathway of RasGRP2 and suppression of apoptosis via inhibition of Bax translocation via its signaling pathway in the human endothelial cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
