title: Different Roles of GRP78 on Cell Proliferation and Apoptosis in Cartilage Development.
abstract: Eukaryotic cells possess several mechanisms to adapt to endoplasmic reticulum (ER) stress and thereby survive. ER stress activates a set of signaling pathways collectively termed as the unfolded protein response (UPR). We previously reported that Bone morphogenetic protein 2 (BMP2) mediates mild ER stress and activates UPR signal molecules in chondrogenesis. The mammalian UPR protects the cell against the stress of misfolded proteins in the endoplasmic reticulum. Failure to adapt to ER stress causes the UPR to trigger apoptosis. Glucose regulated protein 78 (GRP78), as an important molecular chaperone in UPR signaling pathways, is responsible for binding to misfolded or unfolded protein during ER stress. However the influence on GRP78 in BMP2-induced chondrocyte differentiation has not yet been elucidated and the molecular mechanism underlyng these processes remain unexplored. Herein we demonstrate that overexpression of GRP78 enhanced cell proliferation in chondrocyte development with G1 phase advance, S phase increasing and G2-M phase transition. Furthermore, overexpression of GRP78 inhibited ER stress-mediated apoptosis and then reduced apoptosis in chondrogenesis induced by BMP2, as assayed by cleaved caspase3, caspase12, C/EBP homologous protein (CHOP/DDIT3/GADD153), p-JNK (phosphorylated c-Jun N-terminal kinase) expression during the course of chondrocyte differentiation by Western blot. In addition, flow cytometry (FCM) assay, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) assay and immune-histochemistry analysis also proved this result in vitro and in vivo. It was demonstrated that GRP78 knockdown via siRNA activated the ER stress-specific caspase cascade in developing chondrocyte tissue. Collectively, these findings reveal a novel critical role of GRP78 in regulating ER stress-mediated apoptosis in cartilage development and the molecular mechanisms involved.
authors.affiliation: Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing 400016, China. zyxiong38@sina.com.
authors.forename: Zhangyuan
authors.initials: Z
authors.lastname: Xiong
authors.affiliation: Laboratory of Stem Cells and Tissue Engineering, Chongqing Medical University, Chongqing 400016, China. Rongjiang86@sohu.com.
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. xzh11@yahoo.com.
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. yanlii@126.com.
authors.forename: Yanna
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Cell Biology and Genetics, Core Facility of Development Biology, Chongqing Medical University, Chongqing 400016, China. guofengjin919@vip.sohu.com.
authors.forename: Fengjin
authors.initials: F
authors.lastname: Guo
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000235:genetics; D002460:Cell Line; D049109:Cell Proliferation / Q000235:genetics; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D020219:Chondrogenesis / Q000235:genetics*; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000235:genetics; D004722:Endoribonucleases / Q000378:metabolism; D015870:Gene Expression; D006132:Growth Plate / Q000196:embryology / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D015398:Signal Transduction; D046509:Tissue Culture Techniques; D056811:Unfolded Protein Response / Q000235:genetics
chemical_list: D055396:Bone Morphogenetic Protein 2; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C510185:Ern1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases
keywords: ER stress; GRP78; apoptosis; cartilage development; unfolded protein response