title: Silencing of Apoptosis-Inducing factor and poly(ADP-ribose) glycohydrolase reveals novel roles in breast cancer cell death after chemotherapy.
abstract: BACKGROUND
  Cell death induced by poly(ADP-ribose) (PAR) and mediated by apoptosis-inducing factor (AIF) is well-characterized in models of ischemic tissue injury, but their roles in cancer cell death after chemotherapy are less understood.
  
  
  METHODS
  Here we investigated the roles of PAR and AIF by RNA interference (RNAi) in MDA-MB-231 and MCF-7 breast adenocarcinoma cells after chemotherapy. Differences in effects were statistically tested by analysis-of-variance and unpaired student's t-test.
  
  
  RESULTS
  Silencing of AIF by RNAi led to decreased MDA-MB-231 and MCF-7 breast cancer cell death after chemotherapy, which demonstrates a critical role for AIF. RNAi silencing of PAR glycohydrolase (PARG), the primary enzyme that catalyzes the hydrolysis of PAR, led to increased PAR levels but decreased cell death. Further investigation into the possible role of PAR in apoptosis revealed decreased caspase-3/7/8/9 activity in PARG-null cells. Interestingly, the pharmacologic inhibition of caspase activity in PARG-silenced breast cancer cells led to increased cell death after chemotherapy, which indicates that an alternative cell death pathway is activated due to elevated PAR levels and caspase inhibition. AIF silencing in these cells led to profound protection from chemotherapy, which demonstrates that the increased cell death after PARG silencing and caspase inhibition was mediated by AIF.
  
  
  CONCLUSIONS
  The results show a role for AIF in breast cancer cell death after chemotherapy, the ability of PAR to regulate caspase activity, and the ability of AIF to substitute as a primary mediator of breast cancer cell death in the absence of caspases. Thus, the induction of cell death by PAR/AIF may represent a novel strategy to optimize the eradication of breast tumors by activating an alternative cell death pathway.
authors: Department of Pharmaceutical Sciences, College of Pharmacy, Washington State University, P,O, Box 646534, Pullman, WA, 99164-6534, USA.
authors: Xiaoxing
authors: X
authors: Feng
authors: Yiran
authors: Y
authors: Zhou
authors: Alicia M
authors: AM
authors: Proctor
authors: Mandi M
authors: MM
authors: Hopkins
authors: Mengwei
authors: M
authors: Liu
authors: David W
authors: DW
authors: Koh
mesh_terms: D021581:Active Transport, Cell Nucleus; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D051033:Apoptosis Inducing Factor / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D016923:Cell Death / Q000235:genetics; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004249:DNA Damage / Q000187:drug effects; D005260:Female; D020868:Gene Silencing; D006026:Glycoside Hydrolases / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D034622:RNA Interference
chemical_list: D000970:Antineoplastic Agents; D051033:Apoptosis Inducing Factor; D006026:Glycoside Hydrolases; C022407:poly ADP-ribose glycohydrolase; D053181:Caspase 8