title: Activating transcription factor 4, an ER stress mediator, is required for, but excessive ER stress suppresses osteoblastogenesis by bortezomib.
abstract: Endoplasmic reticulum (ER) stress is induced in matrix-producing osteoblasts and plays an essential role in osteoblastogenesis. Although the bone anabolic activity of proteasome inhibitors has been demonstrated, the roles of ER stress induced by proteasome inhibition in osteoblastogenesis remain largely unknown. Here we show that bortezomib translationally increases protein levels of activating transcription factor 4 (ATF4), a downstream mediator of ER stress, in bone marrow stromal cells and MC3T3-E1 preosteoblastic cells. The suppression of ATF4 expression by siRNA abrogated osteocalcin expression and mineralized nodule formation by MC3T3-E1 cells induced by bortezomib, indicating a critical role for ATF4 in bortezomib-mediated osteoblastogenesis. However, bortezomib at 20 nM or higher abolished the mineralized nodule formation along with reductions in the expression of osteoblastogenesis mediators β-catenin and Osterix. Furthermore, at 50 nM, bortezomib induced the expression of C/EBP homologous protein (CHOP), suggesting activation of the ATF4-CHOP pro-apoptotic pathway. These results suggest that a low dose of bortezomib induces osteogenic activity, but that, in contrast, excessive ER stress caused by bortezomib at higher doses hampers osteoblastogenesis. Therefore, dosing schedules for proteasome inhibitors warrant further study to maximize anabolic actions without compromising anti-MM activity in patients with multiple myeloma (MM).
authors.affiliation: Department of Medicine and Bioregulatory Sciences, University of Tokushima Graduate School of Medicine, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan.
authors.forename: Shingen
authors.initials: S
authors.lastname: Nakamura
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Miki
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Kido
authors.forename: Ayako
authors.initials: A
authors.lastname: Nakano
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiasa
authors.forename: Asuka
authors.initials: A
authors.lastname: Oda
authors.forename: Hiroe
authors.initials: H
authors.lastname: Amou
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Watanabe
authors.forename: Takeshi
authors.initials: T
authors.lastname: Harada
authors.forename: Shiro
authors.initials: S
authors.lastname: Fujii
authors.forename: Kyoko
authors.initials: K
authors.lastname: Takeuchi
authors.forename: Kumiko
authors.initials: K
authors.lastname: Kagawa
authors.forename: Shuji
authors.initials: S
authors.lastname: Ozaki
authors.forename: Toshio
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Masahiro
authors.initials: M
authors.lastname: Abe
mesh_terms: D016475:3T3 Cells; D051701:Activating Transcription Factor 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000009:adverse effects / Q000494:pharmacology; D015415:Biomarkers / Q000378:metabolism; D001854:Bone Marrow Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D001897:Boronic Acids / Q000009:adverse effects* / Q000494:pharmacology; D000069286:Bortezomib; D002113:Calcification, Physiologic / Q000187:drug effects; D002478:Cells, Cultured; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D051379:Mice; D009101:Multiple Myeloma / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000187:drug effects* / Q000502:physiology; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects*; D061988:Proteasome Inhibitors / Q000009:adverse effects* / Q000494:pharmacology; D011719:Pyrazines / Q000009:adverse effects* / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000378:metabolism; D017154:Stromal Cells / Q000187:drug effects / Q000502:physiology
chemical_list: D000970:Antineoplastic Agents; D015415:Biomarkers; D001897:Boronic Acids; D009363:Neoplasm Proteins; D061988:Proteasome Inhibitors; D011719:Pyrazines; D034741:RNA, Small Interfering; D015675:Osteocalcin; D051701:Activating Transcription Factor 4; D000069286:Bortezomib