Abstract
Myeloid cell leukemia-1 (Mcl-1) protein is an anti-apoptotic Bcl-2 family protein that plays essential roles in multiple myeloma (MM) survival and drug resistance. In MM, it has been demonstrated that proteasome inhibition can trigger the accumulation of Mcl-1, which has been shown to confer MM cell resistance to bortezomib-induced lethality. However, the mechanisms involved in this unwanted Mcl-1 accumulation are still unclear. The aim of the present study was to determine whether the unwanted Mcl-1 accumulation could be induced by the unfolded protein response (UPR) and to elucidate the role of the endoplasmic reticulum stress response in regulating Mcl-1 expression. Using quantitative RT-PCR and Western blot, we found that the translation of activating transcription factor-4 (ATF4), an important effector of the UPR, was also greatly enhanced by proteasome inhibition. ChIP analysis further revealed that bortezomib stimulated binding of ATF4 to a regulatory site (at position -332 to -324) at the promoter of the Mcl-1 gene. Knocking down ATF4 was paralleled by down-regulation of Mcl-1 induction by bortezomib and significantly increased bortezomib-induced apoptosis. These data identify the UPR and, more specifically, its ATF4 branch as an important mechanism mediating up-regulation of Mcl-1 by proteasome inhibition.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Activating Transcription Factor 4 / genetics
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Activating Transcription Factor 4 / metabolism*
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Antineoplastic Agents / pharmacology
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Apoptosis
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Blotting, Western
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Boronic Acids / pharmacology
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Bortezomib
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Cell Line, Tumor
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Cell Proliferation
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Chromatin Immunoprecipitation
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DNA-Binding Proteins / antagonists & inhibitors
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism
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Endoplasmic Reticulum / metabolism
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Endoplasmic Reticulum Stress / drug effects
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Gene Expression Regulation, Neoplastic*
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Humans
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Multiple Myeloma / drug therapy
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Multiple Myeloma / metabolism*
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Multiple Myeloma / pathology
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Myeloid Cell Leukemia Sequence 1 Protein
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Proto-Oncogene Proteins c-bcl-2 / genetics*
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Proto-Oncogene Proteins c-bcl-2 / metabolism*
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Pyrazines / pharmacology
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RNA Splicing
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RNA, Messenger / genetics
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RNA, Small Interfering / genetics
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Real-Time Polymerase Chain Reaction
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Regulatory Factor X Transcription Factors
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Transcription Factors / antagonists & inhibitors
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Transcription Factors / genetics
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Transcription Factors / metabolism
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Transcription, Genetic
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Unfolded Protein Response / drug effects
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Unfolded Protein Response / physiology*
Substances
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ATF4 protein, human
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Antineoplastic Agents
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Boronic Acids
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DNA-Binding Proteins
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Myeloid Cell Leukemia Sequence 1 Protein
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Proto-Oncogene Proteins c-bcl-2
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Pyrazines
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RNA, Messenger
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RNA, Small Interfering
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Regulatory Factor X Transcription Factors
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Transcription Factors
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Activating Transcription Factor 4
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Bortezomib