title: Ceramide synthase 6 knockdown suppresses apoptosis after photodynamic therapy in human head and neck squamous carcinoma cells.
abstract: BACKGROUND
  The effectiveness of photodynamic therapy (PDT) for cancer treatment correlates with apoptosis. We observed that suppression of de novo-generated sphingolipids, e.g. ceramide, renders cells resistant to apoptosis post-PDT. Ceramide synthase 6 (CerS6) has been implicated in apoptosis after various stimuli.
  
  
  OBJECTIVE
  To investigate the involvement of down-regulation of CerS6 in apoptosis and its impact on the sphingolipid profile post-PDT with the silicone phthalocyanine Pc 4 in a human head and neck squamous carcinoma cell line.
  
  
  METHODS
  Besides siRNA transfections and PDT treatment, immunoblotting for protein expression, mass spectrometry for sphingolipid analysis, spectroflurometry and flow cytometry for apoptotic marker detection, and trypan blue assay for cytotoxicity assessment, were used.
  
  
  RESULTS
  CerS6 knockdown led to reduction in PDT-induced DEVDase activation, mitochondrial depolarization, apoptosis and cell death. CerS6 knockdown was associated with selective decreases in ceramides and dihydroceramides, markedly of C18-dihydroceramide, post-PDT.
  
  
  CONCLUSIONS
  CerS6 might be a novel therapeutic target for regulating apoptotic resistance to PDT.
authors.affiliation: Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, 259 Mack Ave., Detroit, MI 48201, USA. dseparovic@wayne.edu
authors.forename: Duska
authors.initials: D
authors.lastname: Separovic
authors.forename: Paul
authors.initials: P
authors.lastname: Breen
authors.forename: Nicholas
authors.initials: N
authors.lastname: Joseph
authors.forename: Jacek
authors.initials: J
authors.lastname: Bielawski
authors.forename: Jason S
authors.initials: JS
authors.lastname: Pierce
authors.forename: Eric
authors.initials: E
authors.lastname: VAN Buren
authors.forename: Tatyana I
authors.initials: TI
authors.lastname: Gudz
mesh_terms: D001483:Base Sequence; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D017931:DNA Primers; D055785:Gene Knockdown Techniques; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D010778:Photochemotherapy; D051049:Sphingosine N-Acyltransferase / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D008565:Membrane Proteins; C506123:CERS6 protein, human; D051049:Sphingosine N-Acyltransferase