title: The PERK/ATF4/LAMP3-arm of the unfolded protein response affects radioresistance by interfering with the DNA damage response.
abstract: OBJECTIVE
  Lysosome-associated membrane protein 3 (LAMP3) is induced by the PKR-like ER kinase (PERK)/activating transcription factor 4 (ATF4)-arm of the unfolded protein response (UPR) during hypoxia. LAMP3 has prognostic value in breast cancer patients treated with radiotherapy. Here, we specifically investigated the role of the PERK/ATF4/LAMP3-arm in the radiation response of breast cancer cells.
  
  
  METHODS
  Radiosensitivity of breast cancer cells was examined after siRNA-mediated knockdown of PERK, ATF4 and LAMP3. Activation of DNA damage repair proteins was evaluated by Western blotting and immunocytochemistry.
  
  
  RESULTS
  Knockdown of the PERK/ATF4/LAMP3-arm and chemical inhibition of PERK could radiosensitise MDA-MB-231 cells significantly. Western blot analysis of several DNA damage repair proteins showed that LAMP3 knockdowns had an attenuated DNA damage response after radiation compared to controls. γ-H2AX foci analysis revealed that LAMP3 knockdowns had a reduced number of positive cells after irradiation, indicating that their DNA damage repair signalling response is decreased. In addition, the effect of autophagy inhibition was examined and revealed a radiosensitising effect and the presence of residual γ-H2AX foci.
  
  
  CONCLUSIONS
  The PERK/ATF4/LAMP3-arm causes radioresistance of breast cancer cells by increasing DNA damage repair signalling. Inhibition of PERK and/or autophagy may sensitise tumours to radiotherapy.
authors.affiliation: Department of Radiation Oncology, Radboud University Nijmegen Medical Centre, The Netherlands; Department of Laboratory Medicine, Radboud University Nijmegen Medical Centre, The Netherlands.
authors.forename: Anika
authors.initials: A
authors.lastname: Nagelkerke
authors.forename: Johan
authors.initials: J
authors.lastname: Bussink
authors.forename: Albert J
authors.initials: AJ
authors.lastname: van der Kogel
authors.forename: Fred C G J
authors.initials: FC
authors.lastname: Sweep
authors.forename: Paul N
authors.initials: PN
authors.lastname: Span
mesh_terms: D051701:Activating Transcription Factor 4 / Q000037:antagonists & inhibitors / Q000502:physiology*; D001343:Autophagy; D001943:Breast Neoplasms / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D004249:DNA Damage; D005260:Female; D006657:Histones / Q000032:analysis; D006801:Humans; D051907:Lysosomal Membrane Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D054645:Protein Phosphatase 1 / Q000502:physiology; D011836:Radiation Tolerance; D056811:Unfolded Protein Response; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors / Q000502:physiology*; D059666:Lysosomal-Associated Membrane Protein 3
chemical_list: D051701:Activating Transcription Factor 4; D006657:Histones; D051907:Lysosomal Membrane Proteins; D009363:Neoplasm Proteins; D054645:Protein Phosphatase 1; D019892:eIF-2 Kinase; C497109:ATF4 protein, human; C468783:H2AX protein, human; C114233:LAMP3 protein, human; D059666:Lysosomal-Associated Membrane Protein 3; C087519:PPP1R15A protein, human
keywords: Breast cancer; LAMP3; Radiation; Resistance; UPR