NRAS^Q61R mutation drives elevated angiopoietin-2 expression in human endothelial cells and a genetic mouse model

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.

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.

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.

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.