IRE1a constitutes a negative feedback loop with BMP2 and acts as a novel mediator in modulating osteogenic differentiation.
Bone morphogenetic protein 2 (BMP2) is known to activate unfolded protein response (UPR) signaling molecules, such as BiP (IgH chain-binding protein), PERK (PKR-like ER-resistant kinase), and IRE1α. Inositol-requiring enzyme-1a (IRE1a), as one of three unfolded protein sensors in UPR signaling pathways, can be activated during ER stress. Granulin-epithelin precursor (GEP) is an autocrine growth factor that has been implicated in embryonic development, tissue repair, tumorigenesis, and inflammation. However, the influence on IRE1a in BMP2-induced osteoblast differentiation has not yet been elucidated. Herein we demonstrate that overexpression of IRE1a inhibits osteoblast differentiation, as revealed by reduced activity of alkaline phosphatase (ALP) and osteocalcin; however, knockdown of IRE1a via the RNAi approach stimulates osteoblastogenesis. Mechanistic studies revealed that the expression of IRE1a during osteoblast was a consequence of JunB transcription factor binding to several AP1 sequence (TGAG/CTCA) in the 5'-flanking regulatory region of the IRE1a gene, followed by transcription. In addition, GEP induces IRE1a expressions and this induction of IRE1a by GEP depends on JunB. Furthermore, IRE1a inhibition of GEP-induced osteoblastogenesis relies on JunB. Besides, GEP is required for IRE1a inhibition of BMP2-induced bone formation. Collectively, these findings demonstrate that IRE1a negatively regulates BMP2-induced osteoblast differentiation and this IRE1a inhibition effect depends on GEP growth factor. Thus, IRE1a, BMP2, GEP growth factor, and JunB transcription factor form a regulatory loop and act in concert in the course of osteoblastogenesis.
Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing, China.
F-J
FJ
Guo
Laboratory of Stem Cells and Tissue Engineering, Chongqing Medical University, Chongqing, China.
R
R
Jiang
Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing, China.
Z
Z
Xiong
Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing, China.
F
F
Xia
Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing, China.
M
M
Li
Department of Rehabilitation Medicine, State Key Laboratory of Trauma, Burns and Combined Injury, Trauma Center, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, China.
L
L
Chen
Departments of Orthopaedic Surgery and Cell Biology, New York University School of Medicine, New York, NY, USA.
C-J
CJ
Liu
D024506:5' Flanking Region; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D055396:Bone Morphogenetic Protein 2 / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D004722:Endoribonucleases / Q000235:genetics / Q000378:metabolism*; D025461:Feedback, Physiological; D005260:Female; D036341:Intercellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010006:Osteoblasts / Q000378:metabolism*; D015675:Osteocalcin / Q000378:metabolism; D010012:Osteogenesis; D000077153:Progranulins; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D015398:Signal Transduction; D013997:Time Factors; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D036341:Intercellular Signaling Peptides and Proteins; C584097:JunB protein, mouse; D000077153:Progranulins; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D015675:Osteocalcin; C510185:Ern1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases; D000469:Alkaline Phosphatase