Ionizing radiation shifts the PAI-1/ID-1 balance and activates notch signaling in endothelial cells.
OBJECTIVE
Transforming growth factor-beta (TGF-beta) and Notch signaling pathways are important regulators of vascular homeostasis and vessel remodeling; mutations in these pathways can lead to vascular disorders. Similar vascular phenotypes develop in the normal tissues of cancer patients as a long-term effect of radiotherapy. Irradiation most severely affects the capillaries, which become leaky and dilated and might eventually rupture. To investigate the mechanism of such capillary damage, we studied the effect of TGF-beta and Notch signaling in microvascular endothelial cells.


METHODS
Human microvascular endothelial cells were irradiated with 5 or 10 Gy and activation of TGF-beta and Notch signaling pathways was assessed by biochemical methods and a cell migration assay.


RESULTS
Ionizing radiation induced Smad2 phosphorylation and nuclear translocation and increased mRNA and protein expression of the activin-like kinase 5 (ALK5) target gene plasminogen activator inhibitor-1 (PAI-1). At the same time, we observed diminished Smad1/5/8 activation and downregulation of the ALK1 downstream target, inhibitor of DNA binding-1 (ID-1). We also measured an upregulation of the Notch ligand Jagged-1 and the target gene Hey1. Decreased inhibitor of DNA binding-1 levels coincided with a reduced ability of the cells to migrate.


CONCLUSIONS
Ionizing radiation shifts the balance from ALK1 to ALK5 signaling and activates the Notch pathway in endothelial cells. This combination of anti-angiogenic signals contributes to reduced cell migration after irradiation.
Scharpfenecker
Marion
M
Department of Experimental Therapy, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
Kruse
Jacqueline J C M
JJ
Sprong
Debbie
D
Russell
Nicola S
NS
Ten Dijke
Peter
P
Stewart
Fiona A
FA
D030301:Activin Receptors, Type II / Q000378:metabolism; D002465:Cell Movement; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism / Q000528:radiation effects; D004730:Endothelium, Vascular / Q000166:cytology; D055427:Growth Differentiation Factor 2 / Q000494:pharmacology; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1 / Q000378:metabolism*; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism* / Q000528:radiation effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D011832:Radiation Injuries / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D051880:Receptors, Notch / Q000378:metabolism*; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction / Q000528:radiation effects*; D051785:Smad Proteins / Q000378:metabolism; D013684:Telangiectasis / Q000209:etiology*; D014162:Transfection / Q000379:methods; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology
D055427:Growth Differentiation Factor 2; D051798:Inhibitor of Differentiation Protein 1; D017395:Plasminogen Activator Inhibitor 1; D034741:RNA, Small Interfering; D051880:Receptors, Notch; D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; C425364:ACVRL1 protein, human; D030301:Activin Receptors, Type II; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625841:TGFBR1 protein, human