title: DLL4/Notch1 and BMP9 Interdependent Signaling Induces Human Endothelial Cell Quiescence via P27KIP1 and Thrombospondin-1.
abstract: OBJECTIVE
  Bone morphogenetic protein-9 (BMP9)/activin-like kinase-1 and delta-like 4 (DLL4)/Notch promote endothelial quiescence, and we aim to understand mechanistic interactions between the 2 pathways. We identify new targets that contribute to endothelial quiescence and test whether loss of Dll4(+/-) in adult vasculature alters BMP signaling.
  
  
  RESULTS
  Human endothelial cells respond synergistically to BMP9 and DLL4 stimulation, showing complete quiescence and induction of HEY1 and HEY2. Canonical BMP9 signaling via activin-like kinase-1-Smad1/5/9 was disrupted by inhibition of Notch signaling, even in the absence of exogenous DLL4. Similarly, DLL4 activity was suppressed when the basal activin-like kinase-1-Smad1/5/9 pathway was inhibited, showing that these pathways are interdependent. BMP9/DLL4 required induction of P27(KIP1) for quiescence, although multiple factors are involved. To understand these mechanisms, we used proteomics data to identify upregulation of thrombospondin-1, which contributes to the quiescence phenotype. To test whether Dll4 regulates BMP/Smad pathways and endothelial cell phenotype in vivo, we characterized the vasculature of Dll4(+/-) mice, analyzing endothelial cells in the lung, heart, and aorta. Together with changes in endothelial structure and vascular morphogenesis, we found that loss of Dll4 was associated with a significant upregulation of pSmad1/5/9 signaling in lung endothelial cells. Because steady-state endothelial cell proliferation rates were not different in the Dll4(+/-) mice, we propose that the upregulation of pSmad1/5/9 signaling compensates to maintain endothelial cell quiescence in these mice.
  
  
  CONCLUSIONS
  DLL4/Notch and BMP9/activin-like kinase-1 signaling rely on each other's pathways for full activity. This represents an important mechanism of cross talk that enhances endothelial quiescence and sensitively coordinates cellular responsiveness to soluble and cell-tethered ligands.
authors.affiliation: From the Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough.
authors.forename: Bahman
authors.initials: B
authors.lastname: Rostama
authors.affiliation: From the Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough.
authors.forename: Jacqueline E
authors.initials: JE
authors.lastname: Turner
authors.affiliation: From the Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough.
authors.forename: Guy T
authors.initials: GT
authors.lastname: Seavey
authors.affiliation: From the Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough.
authors.forename: Christine R
authors.initials: CR
authors.lastname: Norton
authors.affiliation: From the Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gridley
authors.affiliation: From the Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough.
authors.forename: Calvin P H
authors.initials: CP
authors.lastname: Vary
authors.affiliation: From the Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough. liawl@mmc.org.
authors.forename: Lucy
authors.initials: L
authors.lastname: Liaw
mesh_terms: D030301:Activin Receptors, Type II / Q000235:genetics / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001011:Aorta / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation; D002478:Cells, Cultured; D016922:Cellular Senescence; D003331:Coronary Vessels / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D042783:Endothelial Cells / Q000378:metabolism*; D005838:Genotype; D055427:Growth Differentiation Factor 2; D055412:Growth Differentiation Factors / Q000378:metabolism*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics; D008168:Lung / Q000098:blood supply; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010641:Phenotype; D034622:RNA Interference; D051881:Receptor, Notch1 / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051896:Smad Proteins, Receptor-Regulated / Q000235:genetics / Q000378:metabolism; D019700:Thrombospondin 1 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D030301:Activin Receptors, Type II; D048868:Adaptor Proteins, Signal Transducing; D051792:Basic Helix-Loop-Helix Proteins; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D055427:Growth Differentiation Factor 2; D055412:Growth Differentiation Factors; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D051881:Receptor, Notch1; D012097:Repressor Proteins; D051896:Smad Proteins, Receptor-Regulated; D019700:Thrombospondin 1; C436291:CDKN1B protein, human; C424126:DLL4 protein, human; C519665:DLL4 protein, mouse; C525887:GDF2 protein, human; C485631:HEY1 protein, human; C405693:HEY2 protein, human; C497761:NOTCH1 protein, human; C425364:ACVRL1 protein, human
keywords: BMP9; DLL4; Notch; cell cycle; endothelial cell; quiescence