RasGRF Couples Nox4-Dependent Endoplasmic Reticulum Signaling to Ras

Abstract

Objectives In response to ER stress, endothelial cells initiate corrective pathways such as the unfolded protein response (UPR). Recent studies suggest that reactive oxidant species (ROS) produced on the ER may participate in homeostatic signaling through Ras in response to ER stress. We sought to identify mechanisms responsible for this focal signaling pathway. Approach and Results In endothelial cells we found that ER stress induced by tunicamycin activates the NADPH oxidase Nox4 focally on the ER surface but not on the plasma membrane. Ras activation is also restricted to the ER, occurs downstream of Nox4, and is required for activation of the UPR. In contrast, treatment with the growth factor VEGF results in Ras activation and ROS production confined instead to the plasma membrane and not the ER, demonstrating local coupling of ROS-Ras signals. We further identify the calcium-responsive, ER resident guanyl exchange factors RasGRF1 and RasGRF2 as novel upstream mediators linking Nox4 with Ras activation in response to ER stress. Oxidation of the calcium pump SERCA and increases in cytosolic calcium caused by ER stress are blocked by Nox4 knockdown, and reduction in cytosolic free calcium prevents both Ras activation and the UPR. Conclusions ER stress triggers a localized signaling module on the ER surface involving Nox4-dependent calcium mobilization, which directs local Ras activation through ER-associated, calcium-responsive RasGRF.

Reactive Oxygen Species Generation and Atherosclerosis

“…81 Furthermore, as evidenced in stem cells, ROS were crucial for their differentiation to SMC. 46,47,119 ROS and oxidative stress are involved in regulation of many pathways, for example, stem cell differentiation, response to ER stress, 44 and control of inflammation. Therefore, potential atherosclerosis therapies involving the regulation of oxidative stress levels would require precise …”

“…NADPH oxidases, especially Nox4, play an ambiguous role in the development of atherosclerosis. Craige et al 50 44 ( Figure 2A). Another important player in the ER stress response is XBP1 (X-box-binding protein 1).…”

“…30,31 43 can also aggravate plaque formation. Importantly, basal levels of ROS were crucial for the activation of endoplasmic reticulum (ER) stress response, 44 maintenance of SMC contractile phenotype, 45 or differentiation of SMC from stem cells. 46,47 Thus, the regulation of oxidative stress is complex, and investigation of its role in the pathogenesis of atherosclerosis remains an important subject of many studies.…”

Deletion of RasGRF1 Attenuated Interstitial Fibrosis in Streptozotocin-Induced Diabetic Cardiomyopathy in Mice through Affecting Inflammation and Oxidative Stress

“…The inhibition of RasGRF1 activity by drugs was effective in attenuating aging-induced cardiac fibrosis and heart failure [ 22 ]. In addition, the RasGRF1 also participated in reactive oxidant species production with endoplasmic reticulum (ER) stress [ 16 ]. Although it is known that inflammatory processes and oxidant stress via ER are still the major mechanisms of diabetic cardiomyopathy [ 7 , 8 , 9 ], it is still unclear whether RasGRF1 also regulates the long-term diabetic condition-induced cardiac fibrosis.…”

“…The Ras protein-specific guanine nucleotide releasing factor 1 (RasGRF1) is a family of Ras-selective guanyl exchange factors. The RasGRF1 mediates the activation of inflammation and oxidative stress by regulation of the proteins of the Ras family [ 16 ]. In the rheumatoid arthritis, RasGRF1 has been found to contribute to the production of matrix metalloproteinases by regulating inflammation processes [ 17 ].…”