Implication of oxygen-regulated protein 150 (ORP150) in apoptosis induced by proteasome inhibitors in human thyroid cancer cells.
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.
Gao
Yan-Yan
YY
Department of Biochemistry and Molecular Biology, China Medical University, Shenyang, China.
Liu
Bao-Qin
BQ
Du
Zhen-Xian
ZX
Zhang
Hai-Yan
HY
Niu
Xiao-Fang
XF
Wang
Hua-Qin
HQ
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
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