title: An essential role of discoidin domain receptor 2 (DDR2) in osteoblast differentiation and chondrocyte maturation via modulation of Runx2 activation.
abstract: Discoidin domain receptor 2 (DDR2) belongs to receptor tyrosine kinase (RTK) family and is activated by collagen binding. Although the bone defects in Ddr2 null mice have been reported for a decade, the molecular mechanism remains unclear. This study sought to investigate the function and detailed mechanism of DDR2 in osteogenic and chondrogenic differentiation. Herein we found that in preosteoblastic cells, DDR2 activation was enhanced by osteogenic induction but was not paralleled with the alteration of DDR2 expression. Under differentiated condition, downregulation of endogenous DDR2 through specific shRNA dramatically repressed osteoblastic marker gene expression and osteogenic differentiation. Enforced expression of constitutively activated DDR2 increased the expression of bone markers in both undifferentiated and differentiated osteoblasts. Importantly, molecular evidence showed that DDR2 regulated the transactivity of Runx2, a master transcription factor involved in skeletal development, by modulating its phosphorylation. Analysis of candidate protein kinases indicated that extracellular signal-regulated kinase (ERK) activation is responsive to DDR2 signaling and involved in DDR2 regulation of Runx2 phosphorylation and transcriptional activity. Notably, a gain-of-function mutant of Runx2 with enhanced ERK-independent phosphorylation rescued the impaired osteogenic phenotypes observed in Ddr2-silenced cells, whereas a Runx2 mutant devoid of phosphorylation regulation by ERK inhibited DDR2 induction of osteogenesis. In addition, DDR2 facilitated Runx2 transactivation and type X collagen expression in hypertrophic chondrocytes. Thus this study reveals for the first time that DDR2 plays an essential role in osteoblast and chondrocyte differentiation. The mechanism disclosure may provide therapeutic targets for human genetic disorders caused by DDR2 deficiency.
authors: Department of Biochemistry and Molecular Biology, State Key Laboratory of Cancer Biology, The Fourth Military Medical University, Xi'an, People's Republic of China.
authors: Yan
authors: Y
authors: Zhang
authors: Jin
authors: J
authors: Su
authors: Jiangtian
authors: J
authors: Yu
authors: Xin
authors: X
authors: Bu
authors: Tingting
authors: T
authors: Ren
authors: Xinping
authors: X
authors: Liu
authors: Libo
authors: L
authors: Yao
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D002460:Cell Line; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology*; D024121:Collagen Type X / Q000235:genetics / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D000070818:Discoidin Domain Receptors; D048049:Extracellular Signal-Regulated MAP Kinases; D020869:Gene Expression Profiling; D055785:Gene Knockdown Techniques; D006801:Humans; D006984:Hypertrophy; D020935:MAP Kinase Signaling System; D051379:Mice; D008810:Mice, Inbred C57BL; D010006:Osteoblasts / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology*; D010012:Osteogenesis / Q000235:genetics; D010766:Phosphorylation; D055550:Protein Stability; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011975:Receptors, Mitogen / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000235:genetics
chemical_list: D024121:Collagen Type X; D050659:Core Binding Factor Alpha 1 Subunit; D011975:Receptors, Mitogen; D000070818:Discoidin Domain Receptors; D020794:Receptor Protein-Tyrosine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases