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

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 mutation has been found in the lesions of KLA patients.

Procedure: Our study tested the hypothesis that the NRAS mutation drives elevated Ang-2 expression in endothelial cells. Ang-2 was measured in human endothelial progenitor cells (EPC) expressing NRAS and a genetic mouse model with endothelial targeted NRAS. To determine the signaling pathways driving Ang-2, NRAS EPC were treated with signaling pathway inhibitors.

Results: Ang-2 levels were increased in EPC expressing NRAS compared to NRAS by Western blot analysis of cell lysates and ELISA of the cell culture media. Ang-2 levels were elevated in the blood of NRAS mutant mice. NRAS 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 EPC. However, MEK1/2 inhibitor trametinib was more effective blocking increases in Ang-2.

Conclusions: Our studies show that the NRAS mutation in endothelial cells induces Ang-2 expression in vitro and in vivo. In cultured human endothelial cells, NRAS drives elevated Ang-2 through MAP kinase and mTOR-dependent signaling pathways.