NRAS <sup>Q61R</sup> mutation drives elevated angiopoietin‐2 expression in human endothelial cells and a genetic mouse model
Patricia Pastura, C. Griffin McDaniel, Sara Alharbi, Dermot Fox, Bethany Coleman, Punam Malik, Denise M. Adams, Timothy D. Le Cras
Abstract
Abstract Background Angiopoietin‐2 (Ang‐2) is increased in the blood of patients with kaposiform lymphangiomatosis (KLA) and kaposiform hemangioendothelioma (KHE). While the genetic causes of KHE are not clear, a somatic activating NRAS Q61R mutation has been found in the lesions of KLA patients. Procedure Our study tested the hypothesis that the NRAS Q61R mutation drives elevated Ang‐2 expression in endothelial cells. Ang‐2 was measured in human endothelial progenitor cells (EPC) expressing NRAS Q61R and a genetic mouse model with endothelial targeted NRAS Q61R . To determine the signaling pathways driving Ang‐2, NRAS Q61R EPC were treated with signaling pathway inhibitors. Results Ang‐2 levels were increased in EPC expressing NRAS Q61R compared to NRAS WT by Western blot analysis of cell lysates and ELISA of the cell culture media. Ang‐2 levels were elevated in the blood of NRAS Q61R mutant mice. NRAS Q61R mutant mice also had reduced platelet counts and splenomegaly with hypervascular lesions, like some KLA patients. mTOR inhibitor rapamycin attenuated Ang‐2 expression by NRAS Q61R EPC. However, MEK1/2 inhibitor trametinib was more effective blocking increases in Ang‐2. Conclusions Our studies show that the NRAS Q61R mutation in endothelial cells induces Ang‐2 expression in vitro and in vivo. In cultured human endothelial cells, NRAS Q61R drives elevated Ang‐2 through MAP kinase and mTOR‐dependent signaling pathways.