RASA1 functions in EPHB4 signaling pathway to suppress endothelial mTORC1 activity

J Clin Invest. 2014 Jun;124(6):2774-84. doi: 10.1172/JCI67084. Epub 2014 May 16.

Abstract

Vascular malformations are linked to mutations in RAS p21 protein activator 1 (RASA1, also known as p120RasGAP); however, due to the global expression of this gene, it is unclear how these mutations specifically affect the vasculature. Here, we tested the hypothesis that RASA1 performs a critical effector function downstream of the endothelial receptor EPHB4. In zebrafish models, we found that either RASA1 or EPHB4 deficiency induced strikingly similar abnormalities in blood vessel formation and function. Expression of WT EPHB4 receptor or engineered receptors with altered RASA1 binding revealed that the ability of EPHB4 to recruit RASA1 is required to restore blood flow in EPHB4-deficient animals. Analysis of EPHB4-deficient zebrafish tissue lysates revealed that mTORC1 is robustly overactivated, and pharmacological inhibition of mTORC1 in these animals rescued both vessel structure and function. Furthermore, overexpression of mTORC1 in endothelial cells exacerbated vascular phenotypes in animals with reduced EPHB4 or RASA1, suggesting a functional EPHB4/RASA1/mTORC1 signaling axis in endothelial cells. Tissue samples from patients with arteriovenous malformations displayed strong endothelial phospho-S6 staining, indicating increased mTORC1 activity. These results indicate that deregulation of EPHB4/RASA1/mTORC1 signaling in endothelial cells promotes vascular malformation and suggest that mTORC1 inhibitors, many of which are approved for the treatment of certain cancers, should be further explored as a potential strategy to treat patients with vascular malformations.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Blood Vessels / drug effects
  • Blood Vessels / embryology
  • Blood Vessels / metabolism
  • Endothelial Cells / metabolism
  • Humans
  • Mechanistic Target of Rapamycin Complex 1
  • Multiprotein Complexes / antagonists & inhibitors*
  • Muscular Dystrophy, Animal
  • Receptor, EphB4 / genetics
  • Receptor, EphB4 / metabolism*
  • Signal Transduction
  • TOR Serine-Threonine Kinases / antagonists & inhibitors*
  • Zebrafish / embryology
  • Zebrafish / genetics
  • Zebrafish / metabolism
  • Zebrafish Proteins / genetics
  • Zebrafish Proteins / metabolism*
  • p120 GTPase Activating Protein / deficiency
  • p120 GTPase Activating Protein / genetics
  • p120 GTPase Activating Protein / metabolism*

Substances

  • Multiprotein Complexes
  • Zebrafish Proteins
  • p120 GTPase Activating Protein
  • TOR Serine-Threonine Kinases
  • Receptor, EphB4
  • Mechanistic Target of Rapamycin Complex 1