title: Effects of paclitaxel on permanent head and neck squamous cell carcinoma cell lines and identification of anti-apoptotic caspase 9b.
abstract: OBJECTIVE
  Paclitaxel is an effective chemotherapeutic agent against various human tumors inducing apoptosis via binding to β-tubulin of microtubules and arresting cells mainly in the G2/M phase of the cell cycle. However, the underlying specific molecular mechanisms of paclitaxel on head and neck squamous cell carcinoma (HNSCC) have not been identified yet.
  
  
  METHODS
  The apoptotic effects and mechanisms of paclitaxel on different permanent HPV-negative HNSCC cell lines (UT-SCC-24A, UT-SCC-24B, UT-SCC-60A and UT-SCC-60B) were determined by flow cytometry assays, polymerase chain reaction analysis, immunofluorescence-based assays and sequencing studies.
  
  
  RESULTS
  Paclitaxel induced a G2/M arrest in HNSCC cell lines followed by an increased amount of apoptotic cells. Moreover, the activation of caspase 8, caspase 10 and caspase 3, and the loss of the mitochondrial outer membrane potential could be observed, whereas an activation of caspase 9 could barely be detected. The efficient activation of caspase 9 was not affected by altered methylation patterns. Our results can show that the promoter region of apoptotic protease activating factor 1 (Apaf-1) was not methylated in the HNSCC cell lines. By sequencing analysis two isoforms of caspase 9, the pro-apoptotic caspase 9 and the anti-apoptotic caspase 9b were identified. The anti-apoptotic caspase 9b is missing the catalytic site and acts as an endogenous inhibitor of apoptosis by blocking the binding of caspase 9 to Apaf-1 to form the apoptosome.
  
  
  CONCLUSIONS
  Our data indicate the presence of anti-apoptotic caspase 9b in HNSCC, which may serve as a promising target to increase chemotherapeutic apoptosis induction.
authors.affiliation: Department of Otorhinolaryngology, Clinic for ENT and HNS, University Hospital of Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany. regina.maushagen@gmail.com.
authors.forename: Regina
authors.initials: R
authors.lastname: Maushagen
authors.affiliation: Department of Cardiology and Angiology, University Hospital Münster, Albert-Schweitzer-Campus 1, 48149, Münster, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Reers
authors.affiliation: Department for Nephrology and Hypertension, University Hospital of Schleswig-Holstein, Campus Kiel, Schittenhelmstrasse 12, 24105, Kiel, Germany.
authors.forename: Ann-Christin
authors.initials: AC
authors.lastname: Pfannerstill
authors.affiliation: Department of Molecular Oncology, University Medical Center Mainz, Langenbeckstrasse 1, 55131, Mainz, Germany.
authors.forename: Angelina
authors.initials: A
authors.lastname: Hahlbrock
authors.affiliation: Department of Molecular Oncology, University Medical Center Mainz, Langenbeckstrasse 1, 55131, Mainz, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Stauber
authors.affiliation: Institute of Biomedical Optics, University of Lübeck, Peter-Monnik-Weg 4, 23562, Lübeck, Germany.
authors.forename: Ramtin
authors.initials: R
authors.lastname: Rahmanzadeh
authors.affiliation: Department of Radiation Oncology, University Hospital of Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Rades
authors.affiliation: Department of Otorhinolaryngology, Clinic for ENT and HNS, University Hospital of Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Ralph
authors.initials: R
authors.lastname: Pries
authors.affiliation: Department of Otorhinolaryngology, Clinic for ENT and HNS, University Hospital of Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Wollenberg
mesh_terms: D017398:Alternative Splicing; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D053477:Apoptotic Protease-Activating Factor 1 / Q000235:genetics; D002294:Carcinoma, Squamous Cell / Q000201:enzymology / Q000473:pathology*; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D019175:DNA Methylation; D004789:Enzyme Activation; D006258:Head and Neck Neoplasms / Q000201:enzymology / Q000473:pathology*; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D017239:Paclitaxel / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D000077195:Squamous Cell Carcinoma of Head and Neck; D019311:Staurosporine / Q000494:pharmacology
chemical_list: C506592:APAF1 protein, human; D000972:Antineoplastic Agents, Phytogenic; D053477:Apoptotic Protease-Activating Factor 1; D053453:Caspase 9; D019311:Staurosporine; D017239:Paclitaxel
keywords: Apoptosis; Caspase 9b; Caspases; Head and neck cancer; Paclitaxel