title: RAD9 enhances radioresistance of human prostate cancer cells through regulation of ITGB1 protein levels.
abstract: BACKGROUND
  Mouse embryonic stem cells null for Rad9 are sensitive to deleterious effects of ionizing radiation exposure. Likewise, integrin β1 is a known radioprotective factor. Previously, we showed that RAD9 downregulation in human prostate cancer cells reduces integrin β1 protein levels and ectopic expression of Mrad9 restores inherent high levels.
  
  
  METHODS
  We used RNA interference to knockdown Rad9 expression in PC3 and DU145 prostate cancer cells. These cells were then exposed to ionizing radiation, and integrin β1 protein levels were measured by immunoblotting. Survival of irradiated cells was measured by clonogenicity, cell cycle analysis, PARP-1 cleavage, and trypan blue exclusion.
  
  
  RESULTS
  The function of RAD9 in controlling integrin β1 expression is unique and not shared by the other members of the 9-1-1 complex, HUS1 and RAD1. RAD9 or integrin β1 silencing sensitizes DU145 and PC3 cells to ionizing radiation. Irradiation of DU145 cells with low levels of RAD9 induces cleavage of PARP-1 protein. High levels of ionizing radiation have no effect on integrin β1 protein levels. However, when RAD9 downregulation is combined with 10 Gy of ionizing radiation in DU145 or PC3 cells, there is an additional 50% downregulation of integrin β1 compared with levels in unirradiated RAD9 knockdown cells. Finally, PC3 cells growing on fibronectin display increased radioresistance. However, PC3 cells with RAD9 knockdown are no longer protected by fibronectin after treatment with ionizing radiation.
  
  
  CONCLUSIONS
  Downregulation of RAD9 when combined with ionizing radiation results in reduction of ITGB1 protein levels in prostate cancer cells, and increased lethality.
authors.affiliation: Center for Radiological Research, Columbia University College of Physicians and Surgeons, New York, New York.
authors.forename: Constantinos G
authors.initials: CG
authors.lastname: Broustas
authors.forename: Howard B
authors.initials: HB
authors.lastname: Lieberman
mesh_terms: D018797:Cell Cycle Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D016923:Cell Death / Q000502:physiology; D045744:Cell Line, Tumor; D015536:Down-Regulation; D005092:Exonucleases / Q000235:genetics / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism*; D008297:Male; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000532:radiotherapy*; D011836:Radiation Tolerance
chemical_list: D018797:Cell Cycle Proteins; D005353:Fibronectins; C549605:HUS1 protein, human; D019012:Integrin beta1; C069930:rad9 protein; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D005092:Exonucleases; C113574:Rad1 protein, human
keywords: RAD9; integrin β1; ionizing radiation; prostate cancer
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