GRP78 inhibition enhances ATF4-induced cell death by the deubiquitination and stabilization of CHOP in human osteosarcoma

Jie Luo; Yuanzheng Xia; Jun Luo; Junhe Li; Chao Zhang; Hao Zhang; Ting Ma; Lei Yang; Lingyi Kong

doi:10.1016/j.canlet.2017.09.021

GRP78 inhibition enhances ATF4-induced cell death by the deubiquitination and stabilization of CHOP in human osteosarcoma

Cancer Lett. 2017 Dec 1:410:112-123. doi: 10.1016/j.canlet.2017.09.021. Epub 2017 Sep 22.

Authors

Jie Luo¹, Yuanzheng Xia¹, Jun Luo¹, Junhe Li¹, Chao Zhang¹, Hao Zhang¹, Ting Ma¹, Lei Yang¹, Lingyi Kong²

Affiliations

¹ Jiangsu Key Laboratory of Bioactive Natural Product Research and State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tong Jia Xiang, Nan Jing 210009, China.
² Jiangsu Key Laboratory of Bioactive Natural Product Research and State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tong Jia Xiang, Nan Jing 210009, China. Electronic address: cpu_lykong@126.com.

PMID: 28947141
DOI: 10.1016/j.canlet.2017.09.021

Abstract

New targeted therapies are urgently needed to improve the survival of patients with refractory osteosarcoma (OS). In this study, we show that bortezomib (BTZ), not for OS treatment in the clinic, induces endoplasmic reticulum (ER) stress in U-2 OS cells. Loss of GRP78 sensitizes OS to BTZ with concomitant upregulation of ATF4 and CHOP, which indicates excessive protein synthesis. The relevance of these findings is confirmed in vivo as shown by GRP78 knockdown that delays the growth of U-2 OS xenografts in the presence of BTZ. Here, we demonstrate that MG7, a natural polyyne, can trigger apoptosis. Of note, the apoptotic response to MG7 is dependent on ATF4 but not on the upstream PERK signaling pathway. Interestingly, MG7-induced ATF4 expression does not result in an increase in the levels of CHOP. We demonstrate for the first time that GRP78 physically interacts with the N-terminal domain of CHOP to accelerate its ubiquitination in a p300-dependent manner, which in turn desensitize the tumors to ER stress. Overall, inhibiting GRP78 to strengthen the molecular mechanism of ATF4 via stabilizing CHOP protein may provide a potential vulnerability in OS.

Keywords: ATF4; CHOP; GRP78; Osteosarcoma; Ubiquitination.

MeSH terms

Activating Transcription Factor 4 / genetics
Activating Transcription Factor 4 / metabolism*
Animals
Antineoplastic Agents / pharmacology*
Apoptosis / drug effects
Bone Neoplasms / drug therapy*
Bone Neoplasms / genetics
Bone Neoplasms / metabolism
Bone Neoplasms / pathology
Bortezomib / pharmacology*
Cell Death / drug effects
Cell Line, Tumor
Dose-Response Relationship, Drug
E1A-Associated p300 Protein / metabolism
Endoplasmic Reticulum Chaperone BiP
Endoplasmic Reticulum Stress / drug effects
Gene Expression Regulation, Neoplastic
Heat-Shock Proteins / antagonists & inhibitors*
Heat-Shock Proteins / genetics
Heat-Shock Proteins / metabolism
Humans
Male
Mice, Nude
Osteosarcoma / drug therapy*
Osteosarcoma / genetics
Osteosarcoma / metabolism
Osteosarcoma / pathology
Polyynes / pharmacology*
Protein Binding
Protein Interaction Domains and Motifs
Protein Stability
RNA Interference
Signal Transduction / drug effects
Time Factors
Transcription Factor CHOP / genetics
Transcription Factor CHOP / metabolism*
Transfection
Ubiquitination
Xenograft Model Antitumor Assays

Substances

ATF4 protein, human
Antineoplastic Agents
DDIT3 protein, human
Endoplasmic Reticulum Chaperone BiP
HSPA5 protein, human
Heat-Shock Proteins
Hspa5 protein, mouse
Activating Transcription Factor 4
Transcription Factor CHOP
Polyynes
Bortezomib
E1A-Associated p300 Protein
EP300 protein, human