Cardiovascular Research Advance Access [Accepted Manuscript] published online on May 28, 2008
Cardiovascular Research, doi:10.1093/cvr/cvn128
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Overexpression of ER-resident Chaperone Attenuates Cardiomyocyte Death Induced by Proteasome Inhibition
1 Departments of Cardiovascular Medicine, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871
2 Department of Cardiovascular Medicine, National Cardiovascular Center, Suita, Osaka 565-8565, Japan
Corresponding author: Tetsuo Minamino, MD, PhD Department of Cardiovascular Medicine, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan Tel: 81-6-6879-3472, Fax: 81-6-6879-3473 Email: minamino{at}medone.med.osaka-u.ac.jp
Aims: Proteasome inhibitors are a novel class of anticancer agents that induce tumor cell death via endoplasmic reticulum (ER) stress. Since ER stress is involved in the development of heart failure, we investigated the role of ER-initiated cardiomyocyte death by proteasome inhibition.
Methods: Rat neonatal cardiomyocytes were used in this study. Proteasome activity was assayed using proteasome peptidase substrates. Cell viability and apoptosis were measured by 3-(4,5-dimethylthiazol-2-yl) -2,5-diphenol tetrazolium bromide (MTT) and flow cytometry, respectively. Western blot analysis, real-time PCR and reverse transcriptional PCR were used to detect the expression of protein and messenger RNA. The location of overexpressed glucose-regulated protein (GRP) 78 was observed by confocal fluorescence microscopy.
Results: Proteasome inhibition induced cardiomyocyte death and activated ER stress-induced transcriptional factor ATF6, but not XBP1, without up-regulating ER chaperones. ER-initiated apoptosis signaling including CCAAT enhancer-binding protein (C/EBP) homologous protein (CHOP), c-Jun-N-terminal kinase (JNK) and caspase-12 was activated by proteasome inhibition. Short interference RNA targeting CHOP, but not the blockage of caspase-12 or JNK pathway, attenuated cardiomyocyte death. Overexpression of GRP78 suppressed both CHOP expression and cardiomyocyte death by proteasome inhibition.
Conclusions: These findings demonstrate that proteasome inhibition induces ER-initiated cardiomyocyte death via CHOP-dependent pathways without compensatory up-regulation of ER chaperones. Supplement and/or pharmacological induction of GRP78 can attenuate cardiac damage by proteasome inhibition.
KEYWORDS ER stress; CHOP; GRP78; proteasome inhibition; cardiomyocyte
Time for primary review: 28 days
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Cardiovasc Res 2008 79: 547-548.
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