title: Important role of autophagy in endothelial cell response to ionizing radiation.
abstract: OBJECTIVE
  Vasculature damage is an important contributor to the side-effects of radiotherapy. The aim of this study is to provide insights into the radiobiology of the autophagic response of endothelial cells.
  
  
  METHODS
  Human umbilical vascular endothelial cells (HUVEC) were exposed to 2 Gy of ionizing radiation (IR) and studied using confocal microscopy and western blot analysis, at 4 and 8 days post-irradiation. The role of autophagy flux in HUVEC radio-sensitivity was also examined.
  
  
  RESULTS
  IR-induced accumulation of LC3A(+), LC3B(+) and p62 cytoplasmic vacuoles, while in double immunostaining with lysosomal markers (LAMP2a and CathepsinD) repression of the autophagolysosomal flux was evident. Autophagy-related proteins (ATF4, HIF1α., HIF2α, Beclin1) were, however, induced excluding an eventual repressive effect of radiation on autophagy initiating protein expression. Exposure of HUVEC to SMER28, an mTOR-independent inducer of autophagy, enhanced proLC3 and LC3A, B-I protein expression and accelerated the autophagic flux. Pre-treatment of HUVEC with SMER28 protected against the blockage of autophagic flux induced by IR and conferred radio-resistance. Suppression of LC3A/LC3B proteins with siRNAs resulted in radio-sensitization.
  
  
  CONCLUSIONS
  The current data provide a rationale for the development of novel radioprotection policies targeting the autophagic pathway.
authors.affiliation: Department of Radiotherapy/Oncology, Democritus University of Thrace, and University General Hospital of Alexandroupolis, Alexandroupolis, Greece.
authors.forename: Dimitra
authors.initials: D
authors.lastname: Kalamida
authors.affiliation: Department of Radiotherapy/Oncology, Democritus University of Thrace, and University General Hospital of Alexandroupolis, Alexandroupolis, Greece.
authors.forename: Ilias V
authors.initials: IV
authors.lastname: Karagounis
authors.affiliation: Department of Pathology, Democritus University of Thrace, and University General Hospital of Alexandroupolis, Alexandroupolis, Greece.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Giatromanolaki
authors.affiliation: Department of Radiotherapy/Oncology, Democritus University of Thrace, and University General Hospital of Alexandroupolis, Alexandroupolis, Greece.
authors.forename: Michael I
authors.initials: MI
authors.lastname: Koukourakis
mesh_terms: D000498:Allyl Compounds / Q000008:administration & dosage; D001343:Autophagy / Q000235:genetics* / Q000528:radiation effects; D002402:Cathepsin D / Q000096:biosynthesis; D003593:Cytoplasm / Q000187:drug effects / Q000528:radiation effects / Q000648:ultrastructure; D042783:Endothelial Cells / Q000187:drug effects / Q000528:radiation effects* / Q000648:ultrastructure; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D052119:Lysosomal-Associated Membrane Protein 2 / Q000096:biosynthesis; D008247:Lysosomes / Q000187:drug effects / Q000528:radiation effects* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D018613:Microscopy, Confocal; D011799:Quinazolines / Q000008:administration & dosage; D034741:RNA, Small Interfering; D011839:Radiation, Ionizing
chemical_list: C560309:6-bromo-4-allylamino-quinazoline; D000498:Allyl Compounds; C497811:LAMP2 protein, human; D052119:Lysosomal-Associated Membrane Protein 2; D008565:Membrane Proteins; D011799:Quinazolines; D034741:RNA, Small Interfering; D002402:Cathepsin D