title: Beclin 1 enhances proteasome inhibition-mediated cytotoxicity of thyroid cancer cells in macroautophagy-independent manner.
abstract: BACKGROUND
  The ubiquitin-proteasome system and macroautophagy are two major pathways for intracellular protein degradation. Emerging lines of evidence have shown that blockade of ubiquitin-proteasome system by proteasome inhibitors activates macroautophagy.
  
  
  OBJECTIVE
  The purpose of this study was to determine the involvement of autophagy essential gene Beclin 1 in cytotoxicity of thyroid cancer cells mediated by proteasome inhibitors.
  
  
  METHODS
  Autophagy was measured by acidic-trophic dye staining and EGF-LC3 distribution using fluorescence microscopy, as well as LC3-II transition using Western blot. To ascertain the effect of Beclin 1, cells were transfected with Beclin 1 plasmid or shRNA against Beclin 1. Cell viability and apoptotic cells were measured using MTT assay and flow cytometry, respectively.
  
  
  RESULTS
  Proteasome inhibitors decreased Beclin 1 expression. In addition, treatment with PI3K inhibitors 3-MA or wortmannin, as well as knockdown of Beclin 1 expression, was unable to affect autophagic responses mediated by proteasome inhibitors. Overexpression of Beclin 1 enhanced proteasome inhibitor-mediated cytotoxicity of thyroid cancer cells via suppression of survivin.
  
  
  CONCLUSIONS
  Proteasome inhibitors cause Beclin 1-independent macroautophagic responses of thyroid cancer cells in a Beclin 1-independent manner. Beclin 1 possesses autophagy-independent antitumoral effects upon exposure of thyroid cancer cells to proteasome inhibitors.
authors.affiliation: Department of Geriatrics, the First Affiliated Hospital, China Medical University, Shenyang 110001, China. zhy_doctor@hotmail.com
authors.forename: Hai-Yan
authors.initials: HY
authors.lastname: Zhang
authors.forename: Zhen-Xian
authors.initials: ZX
authors.lastname: Du
authors.forename: Xin
authors.initials: X
authors.lastname: Meng
authors.forename: Zhi-Hong
authors.initials: ZH
authors.lastname: Zong
authors.forename: Hua-Qin
authors.initials: HQ
authors.lastname: Wang
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics* / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects / Q000235:genetics*; D000071186:Beclin-1; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000494:pharmacology; D013964:Thyroid Neoplasms / Q000235:genetics* / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C491997:BECN1 protein, human; D000071186:Beclin-1; D008565:Membrane Proteins; D061988:Proteasome Inhibitors; D046988:Proteasome Endopeptidase Complex