title: Implication of oxygen-regulated protein 150 (ORP150) in apoptosis induced by proteasome inhibitors in human thyroid cancer cells.
abstract: BACKGROUND
  The inhibition of the 26S proteasome may lead to endoplasmic reticulum stress, which has been shown to be implicated in the antitumoral effects of proteasome inhibitors. Oxygen-regulated protein 150 (ORP150) is an inducible endoplasmic reticulum chaperone that is up-regulated after numerous cellular insults and has a cytoprotective role for the maintenance of cellular viability.
  
  
  OBJECTIVE
  The purpose of this study was to determine the involvement of ORP150 in cytotoxicity of thyroid cancer cells mediated by proteasome inhibition.
  
  
  METHODS
  The effects of proteasome inhibition on the expression of ORP150 were analyzed using real-time RT-PCR and Western blot. To ascertain the effect of ORP150, cells were transfected with ORP150 plasmid or small interfering RNA (siRNA) against ORP150, apoptotic cells, and induction of CCAAT/enhancer-binding protein homologous transcription factor (CHOP) mediated by proteasome inhibition were investigated.
  
  
  RESULTS
  ORP150 was induced in thyroid cancer cells after proteasome inhibition. Suppression of activating transcription factor 4 expression by siRNA inhibited the up-regulation of ORP150 mediated by proteasome inhibitors. siRNA for ORP150 stimulated MG132-mediated apoptosis and induction of CHOP, a transcription factor with apoptosis-inducing activity. In contrast, ORP150-overexpressing cells demonstrated less susceptibility to MG132-induced apoptosis and displayed less up-regulation of CHOP. In addition, the sensitizing effect of small interfering ORP150 on apoptosis was suppressed by siRNA for CHOP.
  
  
  CONCLUSIONS
  These results suggest that up-regulation of ORP150 in thyroid cancer cells inhibits MG132-induced apoptosis via suppression of CHOP induction, thereby decreasing the potential antitumor activity of MG132.
authors: Department of Biochemistry and Molecular Biology, China Medical University, Shenyang, China.
authors: Yan-Yan
authors: YY
authors: Gao
authors: Bao-Qin
authors: BQ
authors: Liu
authors: Zhen-Xian
authors: ZX
authors: Du
authors: Hai-Yan
authors: HY
authors: Zhang
authors: Xiao-Fang
authors: XF
authors: Niu
authors: Hua-Qin
authors: HQ
authors: Wang
mesh_terms: D000704:Analysis of Variance; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D018840:HSP70 Heat-Shock Proteins; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D015853:Cysteine Proteinase Inhibitors; C497249:DDIT3 protein, human; D018840:HSP70 Heat-Shock Proteins; D007976:Leupeptins; D018832:Molecular Chaperones; D011506:Proteins; D034741:RNA, Small Interfering; C050087:oxygen-regulated proteins; D051742:Transcription Factor CHOP; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde