The intricate mechanism of PLS3 in bone homeostasis and disease

Since our discovery in 2013 that genetic defects in PLS3 lead to bone fragility, the mechanistic details of this process have remained obscure. It has been established that PLS3 variants cause syndromic and nonsyndromic osteoporosis as well as osteoarthritis. PLS3 codes for an actin-bundling protein with a broad pattern of expression. As such, it is puzzling how PLS3 specifically leads to bone-related disease presentation. Our review aims to summarize the current state of knowledge regarding the function of PLS3 in the predominant cell types in the bone tissue, the osteocytes, osteoblasts and osteoclasts. This is related to the role of PLS3 in regulating mechanotransduction, calcium regulation, vesicle trafficking, cell differentiation and mineralization as part of the complex bone pathology presented by PLS3 defects. Considering the consequences of PLS3 defects on multiple aspects of bone tissue metabolism, our review motivates the study of its mechanism in bone diseases which can potentially help in the design of suitable therapy.

[1]  O. Mäkitie,et al.  Lipocalin-2 is associated with FGF23 in WNT1 and PLS3 osteoporosis , 2022, Frontiers in Endocrinology.

[2]  O. Mäkitie,et al.  Early‐Onset Osteoporosis: Rare Monogenic Forms Elucidate the Complexity of Disease Pathogenesis Beyond Type I Collagen , 2022, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[3]  F. Guan,et al.  Impaired bone strength and bone microstructure in a novel early-onset osteoporotic rat model with a clinically relevant PLS3 mutation , 2022, bioRxiv.

[4]  Farinawati Yazid,et al.  Label-free quantitative proteomic analysis of ascorbic acid-induced differentially expressed osteoblast-related proteins in dental pulp stem cells from deciduous and permanent teeth. , 2022, Current Stem Cell Research & Therapy.

[5]  Y. Qiu,et al.  Identification of a novel splicing mutation and genotype–phenotype correlations in rare PLS3-related childhood-onset osteoporosis , 2022, Orphanet Journal of Rare Diseases.

[6]  Lu Zhang,et al.  X-linked osteogenesis imperfecta accompanied by patent ductus arteriosus: a case with a novel splice variant in PLS3 , 2022, World Journal of Pediatrics.

[7]  Alexandra K O'Donohue,et al.  Curative Cell and Gene Therapy for Osteogenesis Imperfecta , 2022, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[8]  B. Tüysüz,et al.  Osteogenesis imperfecta in 140 Turkish families: Molecular spectrum and, comparison of long-term clinical outcome of those with COL1A1/A2 and biallelic variants , 2021, Bone.

[9]  S. Aradhya,et al.  X-Linked Osteogenesis Imperfecta Possibly Caused by a Novel Variant in PLS3 , 2021, Genes.

[10]  J. Korfage,et al.  Pulsating fluid flow affects pre‐osteoblast behavior and osteogenic differentiation through production of soluble factors , 2021, Physiological reports.

[11]  B. Wirth,et al.  Plastin 3 in health and disease: a matter of balance , 2021, Cellular and Molecular Life Sciences.

[12]  A. Moll,et al.  Ocular characteristics and complications in patients with osteogenesis imperfecta: a systematic review , 2021, Acta ophthalmologica.

[13]  J. Stains,et al.  The Cytoskeleton and Connected Elements in Bone Cell Mechano-Transduction. , 2021, Bone.

[14]  B. Wirth,et al.  Expression and Localization of Thrombospondins, Plastin 3, and STIM1 in Different Cartilage Compartments of the Osteoarthritic Varus Knee , 2021, International journal of molecular sciences.

[15]  O. Mäkitie,et al.  Bone material properties and response to teriparatide in osteoporosis due to WNT1 and PLS3 mutations. , 2021, Bone.

[16]  E. Kudryashova,et al.  Plastin 3 in X-Linked Osteoporosis: Imbalance of Ca2+-Dependent Regulation Is Equivalent to Protein Loss , 2021, Frontiers in Cell and Developmental Biology.

[17]  Jiacan Su,et al.  Targeting actin-bundling protein L-plastin as an anabolic therapy for bone loss , 2020, Science Advances.

[18]  T. Svitkina,et al.  T-Plastin reinforces membrane protrusions to bridge matrix gaps during cell migration , 2020, Nature Communications.

[19]  L. Rubin,et al.  Genetic modifiers ameliorate endocytic and neuromuscular defects in a model of spinal muscular atrophy , 2020, BMC biology.

[20]  J. Klein-Nulend,et al.  The Osteocyte as the New Discovery of Therapeutic Options in Rare Bone Diseases , 2020, Frontiers in Endocrinology.

[21]  E. Egelman,et al.  Osteogenesis imperfecta mutations in plastin 3 lead to impaired calcium regulation of actin bundling , 2020, Bone Research.

[22]  Peng Xu,et al.  PLS3 predicts poor prognosis in pancreatic cancer and promotes cancer cell proliferation via PI3K/AKT signaling , 2020, Journal of cellular physiology.

[23]  O. Mäkitie,et al.  Unique, Gender‐Dependent Serum microRNA Profile in PLS3 Gene‐Related Osteoporosis , 2020, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[24]  L. Bonewald,et al.  The Osteocyte: New Insights. , 2020, Annual review of physiology.

[25]  O. Mäkitie,et al.  Biomarkers in WNT1 and PLS3 Osteoporosis: Altered Concentrations of DKK1 and FGF23 , 2020, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[26]  Hongshan Chen,et al.  S-Nitrosylation of Plastin-3 Exacerbates Thoracic Aortic Dissection Formation via Endothelial Barrier Dysfunction. , 2019, Arteriosclerosis, thrombosis, and vascular biology.

[27]  B. Wirth,et al.  PLS3 Overexpression Delays Ataxia in Chp1 Mutant Mice , 2019, Front. Neurosci..

[28]  Jung-Min Kim,et al.  Bone-targeting AAV-mediated silencing of Schnurri-3 prevents bone loss in osteoporosis , 2019, Nature Communications.

[29]  L. McNamara,et al.  Integrins in Osteocyte Biology and Mechanotransduction , 2019, Current Osteoporosis Reports.

[30]  G. Rus,et al.  Cartilage biomechanics: A key factor for osteoarthritis regenerative medicine. , 2019, Biochimica et biophysica acta. Molecular basis of disease.

[31]  A. Kim,et al.  Engineering of L-Plastin Peptide-Loaded Biodegradable Nanoparticles for Sustained Delivery and Suppression of Osteoclast Function In Vitro , 2019, International journal of cell biology.

[32]  L. McNamara,et al.  Estrogen deficiency impairs integrin αvβ3-mediated mechanosensation by osteocytes and alters osteoclastogenic paracrine signalling , 2019, Scientific Reports.

[33]  O. Mäkitie,et al.  FGF23 and its role in X-linked hypophosphatemia-related morbidity , 2019, Orphanet Journal of Rare Diseases.

[34]  O. Mäkitie,et al.  New Insights Into Monogenic Causes of Osteoporosis , 2019, Front. Endocrinol..

[35]  Zhenlin Zhang,et al.  Genetic variants in the PLS3 gene are associated with osteoporotic fractures in postmenopausal Chinese women , 2019, Acta Pharmacologica Sinica.

[36]  B. Wirth,et al.  Plastin 3 influences bone homeostasis through regulation of osteoclast activity , 2018, Human molecular genetics.

[37]  Y. Wang,et al.  MiR-203 is involved in osteoporosis by regulating DKK1 and inhibiting osteogenic differentiation of MSCs. , 2018, European review for medical and pharmacological sciences.

[38]  N. Bishop,et al.  Novel PLS3 variants in X‐linked osteoporosis: Exploring bone material properties , 2018, American journal of medical genetics. Part A.

[39]  Evangelia Karyka,et al.  Plastin 3 Promotes Motor Neuron Axonal Growth and Extends Survival in a Mouse Model of Spinal Muscular Atrophy , 2018, Molecular therapy. Methods & clinical development.

[40]  T. Li,et al.  Functional analysis of p.Ala253_Leu254insAsn mutation in PLS3 responsible for X‐linked osteoporosis , 2018, Clinical genetics.

[41]  F. Guilak,et al.  Increased Ca2+ signaling through CaV1.2 promotes bone formation and prevents estrogen deficiency-induced bone loss. , 2017, JCI insight.

[42]  Mia M. Thi,et al.  Osteocyte calcium signals encode strain magnitude and loading frequency in vivo , 2017, Proceedings of the National Academy of Sciences.

[43]  W. Möbius,et al.  Hypoxia‐stimulated membrane trafficking requires T‐plastin , 2017, Acta physiologica.

[44]  S. Lindert,et al.  The Roles of Actin-Binding Domains 1 and 2 in the Calcium-Dependent Regulation of Actin Filament Bundling by Human Plastins. , 2017, Journal of molecular biology.

[45]  O. Mäkitie,et al.  PLS3 sequencing in childhood-onset primary osteoporosis identifies two novel disease-causing variants , 2017, Osteoporosis International.

[46]  O. Mäkitie,et al.  Rare Copy Number Variants in Array-Based Comparative Genomic Hybridization in Early-Onset Skeletal Fragility , 2017, Front. Endocrinol..

[47]  O. Mäkitie,et al.  Osteocyte Protein Expression Is Altered in Low-Turnover Osteoporosis Caused by Mutations in WNT1 and PLS3 , 2017, The Journal of clinical endocrinology and metabolism.

[48]  R. Babul‐Hirji,et al.  PLS3 Mutations in X-Linked Osteoporosis: Clinical and Bone Characteristics of Two Novel Mutations , 2017, Hormone Research in Paediatrics.

[49]  Chen Luxenburg,et al.  T-plastin is essential for basement membrane assembly and epidermal morphogenesis , 2017, Science Signaling.

[50]  François Nédélec,et al.  Plastin increases cortical connectivity to facilitate robust polarization and timely cytokinesis , 2017, The Journal of cell biology.

[51]  C. Lorson,et al.  Plastin-3 extends survival and reduces severity in mouse models of spinal muscular atrophy. , 2017, JCI insight.

[52]  J. Hengstler,et al.  TGF-β1 impairs mechanosensation of human osteoblasts via HDAC6-mediated shortening and distortion of primary cilia , 2017, Journal of Molecular Medicine.

[53]  G. Lesca,et al.  A novel homozygous truncating mutation of the SFRP4 gene in Pyle's disease , 2017, Clinical genetics.

[54]  O. Mäkitie,et al.  Teriparatide Treatment in Patients With WNT1 or PLS3 Mutation-Related Early-Onset Osteoporosis: A Pilot Study , 2016, The Journal of clinical endocrinology and metabolism.

[55]  M. Zillikens,et al.  Atypical femur fracture in an adolescent boy treated with bisphosphonates for X-linked osteoporosis based on PLS3 mutation. , 2016, Bone.

[56]  A. Grauer,et al.  Romosozumab Treatment in Postmenopausal Women with Osteoporosis. , 2016, The New England journal of medicine.

[57]  Cristian Suarez,et al.  Internetwork competition for monomers governs actin cytoskeleton organization , 2016, Nature Reviews Molecular Cell Biology.

[58]  Shanjin Huang,et al.  The Structurally Plastic CH2 Domain Is Linked to Distinct Functions of Fimbrins/Plastins* , 2016, The Journal of Biological Chemistry.

[59]  A. Carr,et al.  Osteoarthritis , 2015, The Lancet.

[60]  Marc N. Wein,et al.  The Wnt Inhibitor Sclerostin Is Up-regulated by Mechanical Unloading in Osteocytes in Vitro* , 2015, The Journal of Biological Chemistry.

[61]  K. Malizos,et al.  Comparative proteomic analysis of hypertrophic chondrocytes in osteoarthritis , 2015, Clinical Proteomics.

[62]  O. Mäkitie,et al.  A Novel Splice Mutation in PLS3 Causes X‐linked Early Onset Low‐Turnover Osteoporosis , 2015, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[63]  D. Sillence,et al.  Erratum to: Osteogenesis imperfecta: Clinical diagnosis, nomenclature, and severity assessment , 2015, American Journal of Medical Genetics. Part a.

[64]  T. Carpenter,et al.  Hypophosphatemic Rickets: Lessons from Disrupted FGF23 Control of Phosphorus Homeostasis , 2015, Current Osteoporosis Reports.

[65]  L. Michel,et al.  T-Plastin Expression Downstream to the Calcineurin/NFAT Pathway Is Involved in Keratinocyte Migration , 2014, PloS one.

[66]  F. Glorieux,et al.  Osteoporosis Caused by Mutations in PLS3: Clinical and Bone Tissue Characteristics , 2014, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[67]  P. Gong,et al.  Fluid flow modulates the expression of genes involved in the Wnt signaling pathway in osteoblasts in 3D culture conditions. , 2014, International journal of molecular medicine.

[68]  A. Hofman,et al.  PLS3 mutations in X-linked osteoporosis with fractures , 2014 .

[69]  E. Kudryashova,et al.  Calcium binding is essential for plastin 3 function in Smn-deficient motoneurons. , 2014, Human molecular genetics.

[70]  D. Sillence,et al.  Osteogenesis imperfecta: Clinical diagnosis, nomenclature and severity assessment , 2014, American journal of medical genetics. Part A.

[71]  G. Schmidt,et al.  New insights , 2004 .

[72]  R. Bacabac,et al.  Nitric oxide signaling in mechanical adaptation of bone , 2013, Osteoporosis International.

[73]  Mia M. Thi,et al.  Mechanosensory responses of osteocytes to physiological forces occur along processes and not cell body and require αVβ3 integrin , 2013, Proceedings of the National Academy of Sciences.

[74]  J. Slotta-Huspenina,et al.  Tenascin-C downregulates wnt inhibitor dickkopf-1, promoting tumorigenesis in a neuroendocrine tumor model. , 2013, Cell reports.

[75]  A. Hofman,et al.  PLS3 mutations in X-linked osteoporosis with fractures. , 2013, The New England journal of medicine.

[76]  S. Weinbaum,et al.  Mechanosensation and transduction in osteocytes. , 2013, Bone.

[77]  T. Vincent.  Targeting mechanotransduction pathways in osteoarthritis: a focus on the pericellular matrix. , 2013, Current opinion in pharmacology.

[78]  B. Wirth,et al.  Plastin 3 ameliorates spinal muscular atrophy via delayed axon pruning and improves neuromuscular junction functionality. , 2013, Human molecular genetics.

[79]  A. Haseeb,et al.  Immunopathogenesis of osteoarthritis. , 2013, Clinical immunology.

[80]  Roland Baron,et al.  WNT signaling in bone homeostasis and disease: from human mutations to treatments , 2013, Nature Medicine.

[81]  Kyong-Tai Kim,et al.  Comparative secretome analysis of human bone marrow‐derived mesenchymal stem cells during osteogenesis , 2013, Journal of cellular physiology.

[82]  R. Bacabac,et al.  UvA-DARE ( Digital Academic Repository ) Mechanical loading and how it affects bone cells : the role of the osteocyte cytoskeleton in maintaining our skeleton , 2017 .

[83]  E. Mohammadi,et al.  Barriers and facilitators related to the implementation of a physiological track and trigger system: A systematic review of the qualitative evidence , 2017, International journal for quality in health care : journal of the International Society for Quality in Health Care.

[84]  H. Shinomiya.  Plastin Family of Actin-Bundling Proteins: Its Functions in Leukocytes, Neurons, Intestines, and Cancer , 2012, International journal of cell biology.

[85]  H. Sun,et al.  Mechanotransduction and cartilage integrity , 2011, Annals of the New York Academy of Sciences.

[86]  L. Bonewald,et al.  Conditional deletion of Pkd1 in osteocytes disrupts skeletal mechanosensing in mice , 2011, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[87]  M. Dadlez,et al.  Proteomic characterization of biogenesis and functions of matrix vesicles released from mineralizing human osteoblast-like cells. , 2011, Journal of proteomics.

[88]  Yi Duan,et al.  An Integrative Review of Mechanotransduction in Endothelial, Epithelial (Renal) and Dendritic Cells (Osteocytes) , 2011, Cellular and molecular bioengineering.

[89]  D. Kovar,et al.  Actin Filament Bundling by Fimbrin Is Important for Endocytosis, Cytokinesis, and Polarization in Fission Yeast* , 2011, The Journal of Biological Chemistry.

[90]  Ken-Ichi Kobayashi,et al.  Interaction of activated Rab5 with actin-bundling proteins, L- and T-plastin and its relevance to endocytic functions in mammalian cells. , 2011, Biochemical and biophysical research communications.

[91]  Mark L. Johnson,et al.  Activation of β-catenin signaling in MLO-Y4 osteocytic cells versus 2T3 osteoblastic cells by fluid flow shear stress and PGE2: Implications for the study of mechanosensation in bone. , 2010, Bone.

[92]  M. Chellaiah,et al.  Regulation of Sealing Ring Formation by L-plastin and Cortactin in Osteoclasts* , 2010, The Journal of Biological Chemistry.

[93]  Patrick J Prendergast,et al.  Mechanobiological regulation of the remodelling cycle in trabecular bone and possible biomechanical pathways for osteoporosis. , 2010, Clinical biomechanics.

[94]  Chung-Jui Tsai,et al.  Mechanical stimulation mediates gene expression in MC3T3 osteoblastic cells differently in 2D and 3D environments. , 2010, Journal of biomechanical engineering.

[95]  R. O’Keefe,et al.  β‐catenin, cartilage, and osteoarthritis , 2010, Annals of the New York Academy of Sciences.

[96]  C. Galli,et al.  Osteocytes and WNT: the Mechanical Control of Bone Formation , 2010, Journal of dental research.

[97]  T. Smit,et al.  Paxillin localisation in osteocytes--is it determined by the direction of loading? , 2008, Biochemical and biophysical research communications.

[98]  B. Wirth,et al.  Plastin 3 Is a Protective Modifier of Autosomal Recessive Spinal Muscular Atrophy , 2008, Science.

[99]  Y. Asano,et al.  Conformational analysis of the leukocyte-specific EF-hand protein p65/L-plastin by X-ray scattering in solution. , 2007, Biophysical chemistry.

[100]  M. McKee,et al.  Endocrine Regulation of Energy Metabolism by the Skeleton , 2007, Cell.

[101]  L. Bonewald,et al.  Mechanism by which MLO-A5 Late Osteoblasts/Early Osteocytes Mineralize in Culture: Similarities with Mineralization of Lamellar Bone , 2006, Calcified Tissue International.

[102]  A. Parfitt,et al.  Osteocyte Apoptosis Is Induced by Weightlessness in Mice and Precedes Osteoclast Recruitment and Bone Loss , 2006, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[103]  M. Toyota,et al.  The role of T-fimbrin in the response to DNA damage: silencing of T-fimbrin by small interfering RNA sensitizes human liver cancer cells to DNA-damaging agents. , 2005, International journal of oncology.

[104]  B. Janji,et al.  Actin-filament cross-linking protein T-plastin increases Arp2/3-mediated actin-based movement , 2005, Journal of Cell Science.

[105]  Christophe Ampe,et al.  The actin cytoskeleton in normal and pathological cell motility. , 2004, The international journal of biochemistry & cell biology.

[106]  S. Almo,et al.  Structure of the actin crosslinking core of fimbrin. , 2004, Structure.

[107]  Teruko Takano-Yamamoto,et al.  Terminal Differentiation of Osteoblasts to Osteocytes Is Accompanied by Dramatic Changes in the Distribution of Actin‐Binding Proteins , 2004, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[108]  L. Lanyon,et al.  Mechanical loading: biphasic osteocyte survival and targeting of osteoclasts for bone destruction in rat cortical bone. , 2003, American journal of physiology. Cell physiology.

[109]  Hiroshi Takayanagi,et al.  Induction and activation of the transcription factor NFATc1 (NFAT2) integrate RANKL signaling in terminal differentiation of osteoclasts. , 2002, Developmental cell.

[110]  F. Glorieux,et al.  Deficient Bone Formation in Idiopathic Juvenile Osteoporosis: A Histomorphometric Study of Cancellous Iliac Bone , 2000, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[111]  C. Baird,et al.  The pilot study. , 2000, Orthopedic nursing.

[112]  K. Chihara,et al.  High extracellular calcium inhibits osteoclast-like cell formation by directly acting on the calcium-sensing receptor existing in osteoclast precursor cells. , 1999, Biochemical and biophysical research communications.

[113]  H. Ris,et al.  Osteocyte Shape Is Dependent on Actin Filaments and Osteocyte Processes Are Unique Actin‐Rich Projections , 1998, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[114]  A. Yamaura,et al.  Search for genes involved in UV-resistance in human cells by mRNA differential display: increased transcriptional expression of nucleophosmin and T-plastin genes in association with the resistance. , 1998, Biochemical and biophysical research communications.

[115]  E H Burger,et al.  Microgravity and bone cell mechanosensitivity. , 1998, Bone.

[116]  M. Kuwano,et al.  Increased expression of T‐plastin gene in cisplatin‐resistant human cancer cells: identification by mRNA differential display , 1996, FEBS letters.

[117]  J A Frangos,et al.  Fluid flow stimulates rapid and continuous release of nitric oxide in osteoblasts. , 1996, The American journal of physiology.

[118]  J. Boudreaux,et al.  Synergistic Induction of Osteocalcin Gene Expression , 1996, The Journal of Biological Chemistry.

[119]  C. Hogan.  A matter of balance. , 1995, Australian family physician.

[120]  A. van der Plas,et al.  Sensitivity of osteocytes to biomechanical stress in vitro , 1995, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[121]  J. Chow,et al.  Increased insulin-like growth factor I mRNA expression in rat osteocytes in response to mechanical stimulation. , 1995, The American journal of physiology.

[122]  P. Matsudaira,et al.  Identification of I-plastin, a human fimbrin isoform expressed in intestine and kidney , 1994, Molecular and cellular biology.

[123]  C. Lin,et al.  Human plastin genes. Comparative gene structure, chromosome location, and differential expression in normal and neoplastic cells. , 1993, The Journal of biological chemistry.

[124]  P. Matsudaira,et al.  Fimbrin is a homologue of the cytoplasmic phosphoprotein plastin and has domains homologous with calmodulin and actin gelation proteins , 1990, The Journal of cell biology.

[125]  R. Aebersold,et al.  Molecular cloning and characterization of plastin, a human leukocyte protein expressed in transformed human fibroblasts , 1988 .

[126]  J. Djeu,et al.  Abundant synthesis of the transformation-induced protein of neoplastic human fibroblasts, plastin, in normal lymphocytes. , 1985, Cancer research.

[127]  A. Bretscher.  Fimbrin is a cytoskeletal protein that crosslinks F-actin in vitro. , 1981, Proceedings of the National Academy of Sciences of the United States of America.

[128]  R. Russell,et al.  The formation and orientation of brush border vesicles from rat duodenal mucosa. , 1981, Journal of cell science.

[129]  H. Woodward.  Acquisition , 1979, Critical Inquiry.

[130]  U. Kornak,et al.  Mice lacking plastin-3 display a specific defect of cortical bone acquisition. , 2019, Bone.

[131]  S. Bacon,et al.  Developments in rare bone diseases and mineral disorders , 2018, Therapeutic advances in chronic disease.

[132]  F. Guilak,et al.  Increased Ca 2 + signaling through CaV 1 . 2 promotes bone formation and prevents estrogen deficiency – induced bone loss , 2017 .

[133]  D. Fyhrie,et al.  Modulation of sclerostin expression by mechanical loading and bone morphogenetic proteins in osteogenic cells. , 2009, Biorheology.

[134]  E H Burger,et al.  Signal transduction pathways involved in fluid flow-induced PGE2 production by cultured osteocytes. , 1999, American journal of physiology. Endocrinology and metabolism.

[135]  Raymond Dalgleish,et al.  The human type I collagen mutation database , 1997, Nucleic Acids Res..

[136]  J. Boudreaux,et al.  Synergistic Induction of Osteocalcin Gene Expression IDENTIFICATION OF A BIPARTITE ELEMENT CONFERRING FIBROBLAST GROWTH FACTOR 2 AND CYCLIC AMP RESPONSIVENESS IN THE RAT OSTEOCALCIN PROMOTER* , 1996 .