title: CHOP activation by photodynamic therapy increases treatment induced photosensitization.
abstract: OBJECTIVE
  C/EBP homologous protein (CHOP) is an endoplasmic reticulum (ER) stress inducible transcription factor involved in the development of apoptosis, growth arrest, and differentiation. CHOP deficient (chop - / - ) mouse embryonic fibroblasts (MEFs) exposed to ER stresses such as tunicamycin exhibit decreased apoptosis and reduced toxicity when compared to chop + / + control cells. Overexpression of the 70 kDa heat shock stress protein (HSP-70) can inhibit apoptotic pathways. The biological significance of photodynamic therapy (PDT) protocols that induce cellular damage resulting in differential CHOP and stress protein expression patterns was examined.
  
  
  METHODS
  Wild type mouse radiation induced fibrosarcoma (RIF) cells as well as MEFs with chop + / + and chop - / - genotypes were used with either a mitochondrial and ER localizing porphyrin (PH) photosensitizer or a lysosomal localizing chlorin (NPe6) photosensitizer. PDT induced cytotoxicity, apoptosis, and stress protein expression patterns were determined as a function of cell type and photosensitizer.
  
  
  RESULTS
  PH mediated PDT induced expression of CHOP and 78 kDa glucose regulated protein (GRP-78), but not HSP-70 while NPe6 mediated PDT induced protein expression of HSP-70 but did not activate CHOP or GRP-78 expression. Enhanced apoptosis and toxicity were observed in chop + / + cells following exposure to tunicamycin or PH mediated PDT when compared to identical treatments in chop - / - cells. NPe6 mediated PDT induced minimally detectable apoptosis in both chop + / + and chop - / - cells and only a modest increase in survival for chop - / - cells.
  
  
  CONCLUSIONS
  These results demonstrate that PDT activation of CHOP, GRP-78, and HSP-70 varied as a function of photosensitizer subcellular localization and that a single oxidative stress response was not observed following PDT. We also show that CHOP expression increased apoptosis following PH mediated PDT and that increased CHOP expression is associated with enhanced PDT photosensitization.
authors.affiliation: Division of Hematology-Oncology, Saban Research Institute, Children's Hospital Los Angeles, Los Angeles, California 90027, USA.
authors.forename: Sam
authors.initials: S
authors.lastname: Wong
authors.forename: Marian
authors.initials: M
authors.lastname: Luna
authors.forename: Angela
authors.initials: A
authors.lastname: Ferrario
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Gomer
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D022762:CCAAT-Enhancer-Binding Proteins / Q000096:biosynthesis / Q000187:drug effects*; D018929:Cell Culture Techniques; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis / Q000187:drug effects; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000187:drug effects; D051379:Mice; D018832:Molecular Chaperones / Q000096:biosynthesis / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011166:Porphyrins / Q000494:pharmacology; D051742:Transcription Factor CHOP; D014157:Transcription Factors / Q000096:biosynthesis / Q000187:drug effects*
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; C497250:Ddit3 protein, mouse; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D017319:Photosensitizing Agents; D011166:Porphyrins; D014157:Transcription Factors; D051742:Transcription Factor CHOP; C053434:Talaporfin