title: Focal adhesion kinase silencing augments docetaxel-mediated apoptosis in ovarian cancer cells.
abstract: OBJECTIVE
  Docetaxel causes cell death through induction of apoptosis; however, cell death characteristics for docetaxel have not yet been fully elucidated. We examined the role of focal adhesion kinase (FAK) cleavage in docetaxel-mediated apoptosis.
  
  
  METHODS
  FAK degradation after treatment with docetaxel was determined in both taxane-sensitive (HeyA8 and SKOV3) and taxane-resistant (HeyA8-MDR and SKOV3-TR) ovarian cancer cell lines by Western blot analysis. Cell growth was determined with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. FAK-targeting small interfering RNA (siRNA) was used to decrease FAK expression. Apoptosis and caspase activity were determined using commercially available kits.
  
  
  RESULTS
  SKOV3 and HeyA8 cell lines were both sensitive to docetaxel (IC50 levels, 1-6.2 nmol/L), whereas the SKOV3-TR and HeyA8-MDR cells were resistant (IC50>or=250 nmol/L for both). Docetaxel induced high rates of apoptosis in SKOV3 and HeyA8 cells (84% and 66% apoptosis, respectively) but minimal apoptosis (5-8%) in SKOV3-TR and HeyA8-MDR cells. Similarly, FAK was cleaved in SKOV3 and HeyA8 cells in response to docetaxel treatment but unchanged in the resistant cells. Caspase-3 and caspase-8 activity also increased significantly in docetaxel-treated SKOV3 and HeyA8 cells but not in the taxane-resistant cells. DEVD-fmk (caspase-3 blocker) was able to block both FAK cleavage and apoptosis mediated by docetaxel in SKOV3 and HeyA8 cells. FAK siRNA transfection resulted in 70% to 90% decrease in FAK levels in all cell lines within 72 hours. FAK silencing augmented docetaxel-mediated growth inhibition (5- to 8-fold increase) and apoptosis in both of the taxane-sensitive and taxane-resistant cell lines.
  
  
  CONCLUSIONS
  Docetaxel induces FAK cleavage, mediated through activation of caspase-3, in taxane-sensitive ovarian cancer cells but not in taxane-resistant cells. The absence of FAK degradation may contribute to cell survival in taxane-resistant cells. FAK silencing promotes the in vitro efficacy of docetaxel in both taxane-sensitive and taxane-resistant cell lines and may serve as a novel therapeutic approach.
authors.affiliation: Department of Gynecologic Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Jyotsnabaran
authors.initials: J
authors.lastname: Halder
authors.forename: Charles N
authors.initials: CN
authors.lastname: Landen
authors.forename: Susan K
authors.initials: SK
authors.lastname: Lutgendorf
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.forename: Nicholas B
authors.initials: NB
authors.lastname: Jennings
authors.forename: Dominic
authors.initials: D
authors.lastname: Fan
authors.forename: Gina M
authors.initials: GM
authors.lastname: Nelkin
authors.forename: Rosemarie
authors.initials: R
authors.lastname: Schmandt
authors.forename: Michael D
authors.initials: MD
authors.lastname: Schaller
authors.forename: Anil K
authors.initials: AK
authors.lastname: Sood
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D000077143:Docetaxel; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000201:enzymology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D043823:Taxoids / Q000627:therapeutic use*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D034741:RNA, Small Interfering; D043823:Taxoids; D000077143:Docetaxel; D051416:Focal Adhesion Protein-Tyrosine Kinases; D020169:Caspases