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

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 NRASmutation has been found in the lesions of KLA patients. PROCEDURE: Our study tested the hypothesis that the NRASmutation drives elevated Ang-2 expression in endothelial cells. Ang-2 was measured in human endothelial progenitor cells (EPC) expressing NRASand a genetic mouse model with endothelial targeted NRAS. To determine the signaling pathways driving Ang-2, NRASEPC were treated with signaling pathway inhibitors. RESULTS: Ang-2 levels were increased in EPC expressing NRAScompared to NRASby Western blot analysis of cell lysates and ELISA of the cell culture media. Ang-2 levels were elevated in the blood of NRASmutant mice. NRASmutant mice also had reduced platelet counts and splenomegaly with hypervascular lesions, like some KLA patients. mTOR inhibitor rapamycin attenuated Ang-2 expression by NRASEPC. However, MEK1/2 inhibitor trametinib was more effective blocking increases in Ang-2. CONCLUSIONS: Our studies show that the NRASmutation in endothelial cells induces Ang-2 expression in vitro and in vivo. In cultured human endothelial cells, NRASdrives elevated Ang-2 through MAP kinase and mTOR-dependent signaling pathways.