title: Regulation of chondrocyte differentiation by IRE1α depends on its enzymatic activity.
abstract: Bone morphogenetic protein 2(BMP2) is known to activate unfolded protein response (UPR) signal molecules in chondrogenesis. Inositol-requiring enzyme-1α (IRE1α),as one of three unfolded protein sensors in UPR signaling pathways, can be activated during ER stress. However, the influence on IRE1α in chondrocyte differentiation has not yet been elucidated. Here we present evidence demonstrating that overexpression of IRE1α inhibits chondrocyte differentiation, as revealed by reduced expression of collagen II (ColII), Sox9, collagen X (ColX), matrix metalloproteinase 13 (MMP-13), Indian hedgehog (IHH), Runx2 and enhanced expression of parathyroid hormone-related peptide (PTHrP). Furthermore, IRE1α-mediated inhibition of chondrogenesis depends on its enzymatic activity, since its point mutant lacking enzymatic activity completely loses this activity. The RNase and Kinase domains of IRE1α C-terminal are necessary for its full enzymatic activity and inhibition of chondrocyte differentiation. Mechanism studies demonstrate that granulin-epithelin precursor(GEP), a growth factor known to stimulate chondrogenesis, induced IRE1α expression in chondrogenesis. The expression of IRE1α is depended on GEP signaling, and IRE1α expression is hardly detectable in GEP(-/-) embryos. In addition, IRE1α inhibits GEP-mediated chondrocyte differentiation as a negative regulator. Altered expression of IRE1α in chondrocyte hypertrophy was accompanied by altered levels of IHH and PTHrP. Collectively, IRE1α may be a novel regulator of chondrocyte differentiation by 1) inhibition GEP-mediated chondrocyte differentiation as a negative regulator; 2) promoting IHH/PTHrP signaling.
authors.affiliation: Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing 400016, China. Electronic address: guo.fengjin@gmail.com.
authors.forename: Feng-Jin
authors.initials: FJ
authors.lastname: Guo
authors.affiliation: Laboratory of Stem Cells and Tissue Engineering, Chongqing Medical University, Chongqing 400016, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Jiang
authors.affiliation: Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing 400016, China.
authors.forename: Xiangzhu
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing 400016, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing 400016, China.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Han
authors.affiliation: Departments of Orthopaedic Surgery and Cell Biology, New York University School of Medicine, New York, NY10016, USA.
authors.forename: Chuanju
authors.initials: C
authors.lastname: Liu
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D019902:Chondrocytes / Q000166:cytology* / Q000201:enzymology*; D020219:Chondrogenesis / Q000187:drug effects; D004722:Endoribonucleases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D036341:Intercellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000166:cytology; D051379:Mice; D008807:Mice, Inbred BALB C; D000077153:Progranulins; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D055396:Bone Morphogenetic Protein 2; D036341:Intercellular Signaling Peptides and Proteins; D000077153:Progranulins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C510185:Ern1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases
keywords: BMP2; Chondrogenesis; GEP; Inositol-requiring enzyme-1a (IRE1α); Unfolded protein response