Abstract 21280: Adaptation of Endothelial Notch Responses Through Reversible Acetylation of the Notch1 Intracellular Domain
One of the key functions of blood vessels is to transport nutrients and oxygen to peripheral tissues in the body. An insufficient nutrient and oxygen supply prompts the growth of new blood vessels to meet the metabolic tissue demands. Angiogenic vessel growth is coordinated by Notch signaling and an imbalance in Notch activity can profoundly affect endothelial behavior and vascular growth. However, little is known about the intrinsic regulation and adaptation of endothelial Notch responses. Here, we report a novel mechanism of Notch regulation, which involves the reversible acetylation of the Notch1 intracellular domain (NICD) to adjust the amplitude and duration of endothelial Notch responses. Using mass spectrometry analysis we show that the NICD forms a macromolecular complex with lysine acetyltransferases such as PCAF, the NAD+-dependent deacetylase SIRT1 and the ubiquitin ligase Fbxw7. We find that the NICD is acetylated on several evolutionary conserved lysine residues and that NICD acetylation is associated with enhanced NICD protein stability and Notch activity. SIRT1, in contrast, opposes the acetylation-induced NICD stabilization by removing acetyl groups which otherwise competitively inhibit poly-ubiquitination. Mutation of the NICD lysine acceptor sites renders the NICD resistant towards the SIRT1-mediated inhibition in Notch in signaling. Conditional inactivation of SIRT1 in well-defined models of endothelial Notch signaling (mouse retina, 3D endothelial sprouting) reveals that endothelial cells lacking SIRT1 activity are sensitized to Notch signaling resulting in impaired proliferation, sprout elongation and enhanced Notch target gene expression in response to Notch activation. Our data support a model, in which Notch signaling is dynamically regulated by reversible acetylation and suggest that SIRT1 acts as rheostat to fine-tune endothelial Notch responses. SIRT1, itself regulated by the redox and metabolic state of the cell, could therefore provide an important adaptation mechanism linking tissue oxygenation and nutritional supply to Notch-dependent control of branching vessel morphogenesis.
- © 2010 by American Heart Association, Inc.