title: The retinoblastoma tumor suppressor modulates DNA repair and radioresponsiveness.
abstract: OBJECTIVE
  Perturbations in the retinoblastoma pathway are over-represented in advanced prostate cancer; retinoblastoma loss promotes bypass of first-line hormone therapy. Conversely, preliminary studies suggested that retinoblastoma-deficient tumors may become sensitized to a subset of DNA-damaging agents. Here, the molecular and in vivo consequence of retinoblastoma status was analyzed in models of clinical relevance.
  
  
  METHODS
  Experimental work was performed with multiple isogenic prostate cancer cell lines (hormone sensitive: LNCaP and LAPC4 cells and hormone resistant C42, 22Rv1 cells; stable knockdown of retinoblastoma using shRNA). Multiple mechanisms were interrogated including cell cycle, apoptosis, and DNA damage repair. Transcriptome analysis was performed, validated, and mechanisms discerned. Cell survival was measured using clonogenic cell survival assay and in vivo analysis was performed in nude mice with human derived tumor xenografts.
  
  
  RESULTS
  Loss of retinoblastoma enhanced the radioresponsiveness of both hormone-sensitive and castrate-resistant prostate cancer. Hypersensitivity to ionizing radiation was not mediated by cell cycle or p53. Retinoblastoma loss led to alteration in DNA damage repair and activation of the NF-κB pathway and subsequent cellular apoptosis through PLK3. In vivo xenografts of retinoblastoma-deficient tumors exhibited diminished tumor mass, lower PSA kinetics, and decreased tumor growth after treatment with ionizing radiation (P < 0.05).
  
  
  CONCLUSIONS
  Loss of retinoblastoma confers increased radiosensitivity in prostate cancer. This hypersensitization was mediated by alterations in apoptotic signaling. Combined, these not only provide insight into the molecular consequence of retinoblastoma loss, but also credential retinoblastoma status as a putative biomarker for predicting response to radiotherapy.
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Chellappagounder
authors.initials: C
authors.lastname: Thangavel
authors.affiliation: Department of Surgery, Division of Urology, Glenolden, Pennsylvania, USA.
authors.forename: Ettickan
authors.initials: E
authors.lastname: Boopathi
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Ciment
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Raymond
authors.initials: R
authors.lastname: O'Neill
authors.affiliation: Department of Cancer Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Ankur
authors.initials: A
authors.lastname: Sharma
authors.affiliation: Department of Cancer Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Steve B
authors.initials: SB
authors.lastname: McMahon
authors.affiliation: Department of Cancer Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Biomedical Graduate Studies, University of Pennsylvania, Philadelphia, Pennsylvania, USA.|Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Colorado, USA.
authors.forename: Hestia
authors.initials: H
authors.lastname: Mellert
authors.affiliation: Cancer Genomics, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Sankar
authors.initials: S
authors.lastname: Addya
authors.affiliation: Cancer Genomics, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Ertel
authors.affiliation: Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Ruth
authors.initials: R
authors.lastname: Birbe
authors.affiliation: Cancer Genomics, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Paolo
authors.initials: P
authors.lastname: Fortina
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Adam P
authors.initials: AP
authors.lastname: Dicker
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Department of Cancer Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Department of Urology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Karen E
authors.initials: KE
authors.lastname: Knudsen
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Department of Cancer Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Den
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002453:Cell Cycle / Q000235:genetics; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D004249:DNA Damage / Q000235:genetics; D004260:DNA Repair / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D016328:NF-kappa B / Q000235:genetics; D064129:Prostatic Neoplasms, Castration-Resistant / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics*; D012175:Retinoblastoma / Q000235:genetics*; D016160:Retinoblastoma Protein / Q000235:genetics*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics
chemical_list: D016328:NF-kappa B; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53