title: LIM Mineralization Protein-1 Enhances Bone Morphogenetic Protein-2-Mediated Osteogenesis Through Activation of ERK1/2 MAPK Pathway and Upregulation of Runx2 Transactivity.
abstract: LIM mineralization protein-1 (LMP-1) is an intracellular regulator of bone formation. Upregulation of bone morphogenetic proteins (BMPs) and stabilization of BMP/Smad signaling have been proven to be the key mechanisms through which LMP-1 enhances osteogenesis. However, how LMP-1 regulates BMPs expression and related bone formation remains unclear. In this study, a LMP-1-induced osteogenesis cell model was used to study the molecular action of LMP-1 on BMP-2 expression and bone formation. The results show that overexpression of LMP-1 significantly increases, whereas downregulation of endogenous LMP-1 decreases BMP-2 expression and bone formation. Antagonism of BMP-2 with noggin or short hairpin BMP-2 significantly attenuates the osteoinductive effect of LMP-1, suggesting that the osteoinductive effect of LMP-1 is mediated by BMP-2. LMP-1 regulation of BMP-2 is found to occur at the transcription level using a luciferase reporter assay with a reporter construct containing a BMP-2 promoter. A promoter deletion assay reveals that -1000/-500 bp is the key regulated region by LMP-1. A Runx2-binding site is then located at -934/-920 bp and confirmed by luciferase assay using a reporter construct containing repeats of this Runx2-binding site and the site-directed mutagenesis analysis. Overexpression of LMP-1 significantly increases Runx2 expression. Downregulation of Runx2 expression significantly decreases BMP-2 promoter activity and BMP-2 expression. A ChIP assay demonstrates that LMP-1 increases the interaction between Runx2 and BMP-2 promoter. A luciferase reporter assay using the OSE2 promoter containing a Runx2-binding site confirms that Runx2 transactivity can be upregulated by LMP-1. Moreover, inhibiting the activation of different pathways with specific pathway inhibitors reveals that ERK1/2 MAPK activation is essential for LMP-1-induced upregulation of Runx2 transactivity and subsequent BMP-2 expression. In conclusion, our novel findings describe a positive regulatory effect of LMP-1 on BMP-2 expression and BMP-2-mediated osteogenesis. This effect occurs through activation of ERK1/2 pathway and subsequent upregulation of Runx2 transactivity.
authors: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors: Hehai
authors: H
authors: Pan
authors: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors: Xiang
authors: X
authors: Li
authors: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors: Jianru
authors: J
authors: Wang
authors: Department of Orthopedics, The Fifth Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors: Kuibo
authors: K
authors: Zhang
authors: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors: Hao
authors: H
authors: Yang
authors: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors: Zemin
authors: Z
authors: Li
authors: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors: Zhaomin
authors: Z
authors: Zheng
authors: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors: Hui
authors: H
authors: Liu
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000096:biosynthesis* / Q000235:genetics; D002460:Cell Line; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D060588:LIM Domain Proteins / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C525719:Bmp2 protein, mouse; C525720:Bmp2 protein, rat; D055396:Bone Morphogenetic Protein 2; D050659:Core Binding Factor Alpha 1 Subunit; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; C484381:Pdlim7 protein, mouse; C099008:Pdlim7 protein, rat; C493716:Runx2 protein, mouse; C493717:Runx2 protein, rat; D048052:Mitogen-Activated Protein Kinase 3
keywords: BMP-2; ERK1/2; LMP-1; OSTEOGENESIS; RUNX2