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David R Clemmons - One of the best experts on this subject based on the ideXlab platform.
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estrogen stimulation of pleiotrophin enhances osteoblast differentiation and maintains bone mass in igfbp 2 null mice
Endocrinology, 2020Co-Authors: Victoria E Demambro, Clifford J Rosen, Susan Dcosta, Shalier K Xia, Zach C Cox, David R ClemmonsAbstract:Insulin-like growth factor binding protein-2 (IGFBP-2) stimulates osteoblast differentiation but only male IGFBP2 null mice have a skeletal phenotype. The trophic actions of IGFBP-2 in bone are mediated through its binding to receptor tyrosine phosphatase beta (RPTPβ). Another important ligand for RPTPβ is pleiotrophin (PTN), which also stimulates osteoblast differentiation. We determined the change in PTN and RPTPβ in IGFBP2-/- mice. Analysis of whole bone mRNA in wild-type and knockout mice revealed increased expression of Ptn. Rptpβ increased in gene-deleted animals with females having greater expression than males. Knockdown of PTN expression in osteoblasts in vitro inhibited differentiation, and addition of PTN to the incubation medium rescued the response. Estradiol stimulated PTN secretion and PTN knockdown blocked estradiol-stimulated differentiation. PTN addition to IGFBP-2 silenced osteoblast stimulated differentiation, and an anti-fibronectin-3 antibody, which inhibits PTN binding to RPTPβ, inhibited this response. Estrogen stimulated PTN secretion and downstream signaling in the IGFBP-2 silenced osteoblasts and these effects were inhibited with anti-fibronectin-3. Administration of estrogen to wild-type and IGFBP2-/- male mice stimulated an increase in both areal bone mineral density and trabecular bone volume fraction but the increase was significantly greater in the IGFBP2-/- animals. Estrogen also stimulated RPTPβ expression in the null mice. We conclude that loss of IGFBP-2 expression is accompanied by upregulation of PTN and RPTPβ expression in osteoblasts, that the degree of increase is greater in females due to estrogen secretion, and that this compensatory change may account for some component of the maintenance of normal bone mass in female mice.
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insulin like growth factor binding protein 2 is required for osteoclast differentiation
Journal of Bone and Mineral Research, 2012Co-Authors: Victoria E Demambro, Clifford J Rosen, Masanobu Kawai, Laura A Maile, Christine Wai, Teresa Cascella, David R ClemmonsAbstract:Global deletion of the IGFBP2 gene results in the suppression of bone turnover. To investigate the role of insulin-like growth factor-binding protein-2 (IGFBP-2) in regulating osteoclast differentiation, we cultured IGFBP2−/− bone marrow cells and found a reduction in the number of osteoclasts and impaired resorption. Addition of full-length IGFBP-2 restored osteoclast differentiation, fusion, and resorption. To determine the molecular domains of IGFBP-2 that were required for this effect to be manifest, IGFBP2−/− bone marrow cells were transfected with constructs in which the heparin-binding (HBD) or the IGF-binding domains of IGFBP-2 were mutated. We found that both domains were necessary for osteoclastogenesis because expression of the mutated forms of either domain failed to support the formation of functionally mature osteoclasts. To discern the mechanism by which IGFBP-2 regulates osteoclast formation, PTEN abundance and phosphorylation status as well as AKT responsiveness to IGF-I were analyzed. IGFBP2−/− cells had elevated levels of PTEN and phospho-PTEN compared with controls. Expression of wild-type IGFBP-2 reduced the level of PTEN to that of wild-type cells. Cells expressing the IGF-binding mutant showed suppression of PTEN and phospho-PTEN equivalent to the wild-type protein, whereas those expressing the IGFBP-2 HBD mutant showed no PTEN suppression. When the ability of IGF-I to stimulate AKT activation, measured by Thr308 and Ser473 phosphorylation, was analyzed, stimulation of Ser473 in response to IGF-I in preosteoclasts required the presence of intact IGFBP-2. This effect was duplicated by the addition of a CK2 inhibitor that prevents the phosphorylation of PTEN. In contrast, in fully differentiated osteoclasts, stimulation of Thr308 phosphorylation required the presence of intact IGFBP-2. We conclude that IGFBP-2 is an important regulator of osteoclastogenesis and that both the heparin- and the IGF-binding domains of IGFBP-2 are essential for the formation of fully differentiated and functional osteoclasts. © 2012 American Society for Bone and Mineral Research
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the heparin binding domain of igfbp 2 has insulin like growth factor binding independent biologic activity in the growing skeleton
Journal of Biological Chemistry, 2011Co-Authors: Masanobu Kawai, Victoria E Demambro, David R Clemmons, Mary L Bouxsein, Wesley G Beamer, Ernesto Canalis, Anne Breggia, Xinchun Shen, Clifford J RosenAbstract:Insulin-like growth factor-binding protein 2 (IGFBP-2) is a member of a family of six highly conserved IGFBPs that are carriers for the insulin-like growth factors (IGFs). IGFBP-2 levels rise during rapid neonatal growth and at the time of peak bone acquisition. In contrast, IGFBP2−/− mice have low bone mass accompanied by reduced osteoblast numbers, low bone formation rates, and increased PTEN expression. In the current study, we postulated that IGFBP-2 increased bone mass partly through the activity of its heparin-binding domain (HBD). We synthesized a HBD peptide specific for IGFBP-2 and demonstrated in vitro that it rescued the mineralization phenotype of IGFBP2−/− bone marrow stromal cells and calvarial osteoblasts. Consistent with its cellular actions, the HBD peptide ex vivo stimulated metacarpal periosteal expansion. Furthermore, administration of HBD peptide to IGFBP2−/− mice increased osteoblast number, suppressed marrow adipogenesis, restored trabecular bone mass, and reduced bone resorption. Skeletal rescue in the IGFBP2−/− mice was characterized by reduced PTEN expression followed by enhanced Akt phosphorylation in response to IGF-I and increased β-catenin signaling through two mechanisms: 1) stimulation of its cytosolic accumulation and 2) increased phosphorylation of serine 552. We conclude that the HBD peptide of IGFBP-2 has anabolic activity by activating IGF-I/Akt and β-catenin signaling pathways. These data support a growing body of evidence that IGFBP-2 is not just a transport protein but rather that it functions coordinately with IGF-I to stimulate growth and skeletal acquisition.
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gender specific changes in bone turnover and skeletal architecture in igfbp 2 null mice
Endocrinology, 2008Co-Authors: Victoria E Demambro, David R Clemmons, Lindsay G Horton, Mary L Bouxsein, Teresa L Wood, Wesley G Beamer, Ernesto Canalis, Clifford J RosenAbstract:IGF-binding protein-2 (IGFBP-2) is a 36-kDa protein that binds to the IGFs with high affinity. To determine its role in bone turnover, we compared IGFBP2−/− mice with IGFBP2+/+ colony controls. IGFBP2−/− males had shorter femurs and were heavier than controls but were not insulin resistant. Serum IGF-I levels in IGFBP2−/− mice were 10% higher than IGFBP2+/+ controls at 8 wk of age; in males, this was accompanied by a 3-fold increase in hepatic Igfbp3 and Igfbp5 mRNA transcripts compared with IGFBP2+/+ controls. The skeletal phenotype of the IGFBP2−/− mice was gender and compartment specific; IGFBP2−/− females had increased cortical thickness with a greater periosteal circumference compared with controls, whereas male IGFBP2−/− males had reduced cortical bone area and a 20% reduction in the trabecular bone volume fraction due to thinner trabeculae than IGFBP2+/+ controls. Serum osteocalcin levels were reduced by nearly 40% in IGFBP2−/− males, and in vitro, both CFU-ALP+ preosteoblasts, and tartrate-resistant acid phosphatase-positive osteoclasts were significantly less abundant than in IGFBP2+/+ male mice. Histomorphometry confirmed fewer osteoblasts and osteoclasts per bone perimeter and reduced bone formation in the IGFBP2−/− males. Lysates from both osteoblasts and osteoclasts in the IGFBP2−/− males had phosphatase and tensin homolog (PTEN) levels that were significantly higher than IGFBP2+/+ controls and were suppressed by addition of exogenous IGFBP-2. In summary, there are gender- and compartment-specific changes in IGFBP2−/− mice. IGFBP-2 may regulate bone turnover in both an IGF-I-dependent and -independent manner.
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differential expression and biological effects of insulin like growth factor binding protein 4 and 5 in vascular smooth muscle cells
Journal of Biological Chemistry, 1998Co-Authors: Cunming Duan, David R ClemmonsAbstract:Abstract Insulin-like growth factor-I (IGF-I) plays an important role in regulating vascular smooth muscle cell (VSMC) proliferation, migration, and apoptosis. The bioactivity of IGF-I is modulated by a group of high affinity, specific binding proteins (IGF-binding proteins; IGFBPs) that are present in the interstitial fluid. Previously, we have reported that porcine VSMCs synthesize and secrete IGF-I and several forms of IGFBPs, including IGFBP-2, IGFBP-4, and IGFBP-5. In this study, we examined the role of autocrine/paracrine secreted IGF-I in controlling the expression of IGFBP-4 and IGFBP-5 as well as the effects of these IGFBPs in modulating the cellular replication response to IGF-I. The concentrations of IGFBP-4 in the conditioned medium increased significantly from <50 ng/ml to 742 ± 105 ng/ml. This increase was associated with a decrease in the activity of an IGF-I-regulated IGFBP-4 protease. In contrast, the synthesis of IGFBP-5 was inversely correlated with culture density, and its concentration decreased from 792 ± 91 to 44 ± 14 ng/ml. IGFBP-5 mRNA in sparse cultures was 3-fold higher compared with those in confluent cultures. This culture density-dependent change in IGFBP-5 mRNA correlated closely with endogenous IGF-I levels. Since treatment of VSMC with exogenous IGF-I increased IGFBP-5 mRNA levels, we neutralized the effect of endogenously secreted IGF-I with an anti-IGF-I antibody to determine if it would alter IGFBP-5 mRNA abundance. This resulted in a 4.4-fold decrease in IGFBP-5 mRNA levels. When added together with IGF-I, exogenous IGFBP-4 inhibited IGF-I-induced DNA synthesis in a concentration-dependent manner. IGFBP-5, on the other hand, potentiated the effect of IGF-I. Therefore, IGFBP-4 and IGFBP-5 appear to be differentially regulated by autocrine/paracrine IGF-I through distinct mechanisms. These two proteins, in turn, play opposing roles in modulating IGF-I action in stimulating VSMC proliferation.
Ron G Rosenfeld - One of the best experts on this subject based on the ideXlab platform.
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the insulin like growth factor binding protein igfbp superfamily
Endocrine Reviews, 1999Co-Authors: Vivian Hwa, Ron G RosenfeldAbstract:Over the last decade, the concept of an IGFBP family has been well accepted, based on structural similarities and on functional abilities to bind IGFs with high affinities. The existence of other potential IGFBPs was left open. The discovery of proteins with N-terminal domains bearing striking structural similarities to the N terminus of the IGFBPs, and with reduced, but demonstrable, affinity for IGFs, raised the question of whether these proteins were "new" IGFBPs (22, 23, 217). The N-terminal domain had been uniquely associated with the IGFBPs and has long been considered to be critical for IGF binding. No other function has been confirmed for this domain to date. Thus, the presence of this important IGFBP domain in the N terminus of other proteins must be considered significant. Although these other proteins appear capable of binding IGF, their relatively low affinity and the fact that their major biological actions are likely to not directly involve the IGF peptides suggest that they probably should not be classified within the IGFBP family as provisionally proposed (22, 23). The conservation of this single domain, so critical to high-affinity binding of IGF by the six IGFBPs, in all of the IGFBP-rPs, as well, speaks to its biological importance. Historically, and perhaps, functionally, this has led to the designation of an "IGFBP superfamily". The classification and nomenclature for the IGFBP superfamily, are, of course, arbitrary; what is ultimately relevant is the underlying biology, much of which still remains to be deciphered. The nomenclature for the IGFBP related proteins was derived from a consensus of researchers working in the IGFBP field (52). Obviously, a more general consensus on nomenclature, involving all groups working on each IGFBP-rP, has yet to be reached. Further understanding of the biological functions of each protein should help resolve the nomenclature dilemma. For the present, redesignating these proteins IGFBP-rPs simplifies the multiple names already associated with each IGFBP related protein, and reinforces the concept of a relationship with the IGFBPs. Beyond the N-terminal domain, there is a lack of structural similarity between the IGFBP-rPs and IGFBPs. The C-terminal domains do share similarities to other internal domains found in numerous other proteins. For example, the similarity of the IGFBP C terminus to the thyroglobulin type-I domain shows that the IGFBPs are also structurally related to numerous other proteins carrying the same domain (87). Interestingly, the functions of the different C-terminal domains in members of the IGFBP superfamily include interactions with the cell surface or ECM, suggesting that, even if they share little sequence similarities, the C-terminal domains may be functionally related. The evolutionary conservation of the N-terminal domain and functional studies support the notion that IGFBPs and IGFBP-rPs together form an IGFBP superfamily. A superfamily delineates between closely related (classified as a family) and distantly related proteins. The IGFBP superfamily is therefore composed of distantly related families. The modular nature of the constituents of the IGFBP superfamily, particularly their preservation of an highly conserved N-terminal domain, seems best explained by the process of exon shuffling of an ancestral gene encoding this domain. Over the course of evolution, some members evolved into high-affinity IGF binders and others into low-affinity IGF binders, thereby conferring on the IGFBP superfamily the ability to influence cell growth by both IGF-dependent and IGF-independent means (Fig. 10). A final word, from Stephen Jay Gould (218): "But classifications are not passive ordering devices in a world objectively divided into obvious categories. Taxonomies are human decisions imposed upon nature--theories about the causes of nature's order. The chronicle of historical changes in classification provides our finest insight into conceptual revolutions
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identification of a family of low affinity insulin like growth factor binding proteins igfbps characterization of connective tissue growth factor as a member of the igfbp superfamily
Proceedings of the National Academy of Sciences of the United States of America, 1997Co-Authors: Hoseong Kim, Srinivasa R Nagalla, Elizabeth M Wilson, Charles Roberts, Ron G RosenfeldAbstract:The insulin-like growth factor (IGF) binding proteins (IGFBPs) modulate the actions of the insulin-like growth factors in endocrine, paracrine, and autocrine settings. Additionally, some IGFBPs appear to exhibit biological effects that are IGF independent. The six high-affinity IGFBPs that have been characterized to date exhibit 40–60% amino acid sequence identity overall, with the most conserved sequences in their NH2 and COOH termini. We have recently demonstrated that the product of the mac25/IGFBP-7 gene, which shows significant conservation in the NH2 terminus, including an “IGFBP motif” (GCGCCXXC), exhibits low-affinity IGF binding. The closely related mammalian genes connective tissue growth factor (CTGF) gene, nov, and cyr61 encode secreted proteins that also contain the conserved sequences and IGFBP motifs in their NH2 termini. To ascertain if these genes, along with mac25/IGFBP-7, encode a family of low-affinity IGFBPs, we assessed the IGF binding characteristics of recombinant human CTGF (rhCTGF). The ability of baculovirus-synthesized rhCTGF to bind IGFs was demonstrated by Western ligand blotting, affinity cross-linking, and competitive affinity binding assays using 125I-labeled IGF-I or IGF-II and unlabeled IGFs. CTGF, like mac25/IGFBP-7, specifically binds IGFs, although with relatively low affinity. On the basis of these data, we propose that CTGF represents another member of the IGFBP family (IGFBP-8) and that the CTGF gene, mac25/IGFBP-7, nov, and cyr61 are members of a family of low-affinity IGFBP genes. These genes, along with those encoding the high-affinity IGFBPs 1–6, together constitute an IGFBP superfamily whose products function in IGF-dependent or IGF-independent modes to regulate normal and neoplastic cell growth.
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insulin like growth factor binding proteins igfbps and their regulatory dynamics
The International Journal of Biochemistry & Cell Biology, 1996Co-Authors: Kevin M Kelley, Sharron E Gargosky, Zoran Gucev, Tomoko Matsumoto, Vivian Hwa, Diane M Simpson, Ron G RosenfeldAbstract:The IGFBPs are a family of homologous proteins that have co-evolved with the IGFs and that confer upon the IGF regulatory system both functional and tissue specificity. IGFBPs are not merely carrier proteins for IGFs, but hold a central position in IGF ligand-receptor interactions through influences on both the bioavailability and distribution of IGFs in the extracellular environment. In addition, IGFBPs appear to have intrinsic biological activity independent of IGFs. The current status of research on IGFBPs is reviewed herein. Following a brief introduction to the entire IGF/IGFBP system, separate sections for each of the six cloned mammalian IGFBPs, the most extensive for IGFBP3, cover selected topics that emphasize the dynamics of IGFBPs—that is, their regulation in cells, their functionally important post-translational modifications, and their interactions in the cellular microenvironment—and how these dynamics influence physiological function.
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insulin like growth factors and their binding proteins in the term and preterm human fetus and neonate with normal and extremes of intrauterine growth
The Journal of Clinical Endocrinology and Metabolism, 1995Co-Authors: Linda C Giudice, Sharron E Gargosky, F De Zegher, B A Dsupin, L De Las Fuentes, R A Crystal, Raymond L Hintz, Ron G RosenfeldAbstract:Insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs), and insulin are believed to be important in the regulation of fetal and neonatal growth. We previously reported that the profiles of IGFBPs in fetal cord serum (FCS) were dependent on the growth/metabolic status of the fetus. The goals of the current study were to examine the IGF system in FCS from term fetuses with normal growth, those with intrauterine growth retardation (IUGR), and those who were large for gestational age (LGA) and in FCS from normal weight preterm (25-37 weeks) and term fetuses in the neonatal period from the day of birth (day 0) until 7 days of age (day 7). Western ligand blotting (WLB) of term FCS revealed IGFBPs with mol wt of 43 and 38 kilodaltons (kDa; IGFBP-3), 34 kDa (IGFBP-2), 28 kDa (IGFBP-1 and glycosylated IGFBP-4), and 24 kDa (IGFBP-4). In IUGR FCS, there was a 50% decrease in IGFBP-3 detected by WLB, which was shown not to be due to an IGFBP-3 protease in IUGR sera. In LGA FCS, IGFBP-3 levels were elevated...
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differential effects of insulin like growth factor igf i and igf ii on the expression of igf binding proteins igfbps in a rat neuroblastoma cell line isolation and characterization of two forms of igfbp 4
Endocrinology, 1991Co-Authors: Paolo G Ceda, Paul J Fielder, William J Henzel, Andrea Louie, Sharon M Donovan, Andrew R Hoffman, Ron G RosenfeldAbstract:The isolation and hormonal regulation of two low molecular weight insulin-like growth factor binding proteins (IGFBPs) present in the conditioned medium (CM) of the rat neuroblastoma cell line B104 cells has been performed. IGFBPs were purified by ZnSO4 precipitation, insulin-like growth factor- I 1IGF-I) affinity chromatography, and reverse phase HPLC. Final isolation and N-terminal analysis was accomplished by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, electroblotting to polyvinylidene difluoride membranes, and sequencing of the bound proteins. Two IGFBPs, with apparent Mr of 28K and 24K were coisolated and sequenced. Both proteins had identical N-terminal sequences and appear to be two forms of IGFBP-4. Treatment of the IGFBPs with endoglycosidase-F caused a shift in the apparent Mr of the 28K IGFBP to 24K. However, there was no change in the apparent Mr of the 24K IGFBP. The data from this study suggest that the IGFBP-4 exists as both a glycosylated and nonglycosylated protein. Treatme...
William Yk Hwang - One of the best experts on this subject based on the ideXlab platform.
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low dose insulin like growth factor binding proteins 1 and 2 and angiopoietin like protein 3 coordinately stimulate ex vivo expansion of human umbilical cord blood hematopoietic stem cells as assayed in nod scid gamma null mice
Stem Cell Research & Therapy, 2014Co-Authors: Xiubo Fan, Francesca Wi Lim, Justina Ml Ang, Pat Py Chu, Sudipto Bari, William Yk HwangAbstract:Introduction Insulin-like growth factors (IGFs), IGF binding proteins (IGFBPs) and angiopoietin-like proteins (ANGPTLs) can enhance the ex vivo expansion of hematopoietic stem cells (HSCs) when used with a standard cytokine cocktail of stem cell factor (SCF), thrombopoietin (TPO) and FLT3 ligand (FL). In order to determine the optimal dose and combination of IGFs, IGFBPs and ANGPTLs, serial dilution and full permutation of IGFBP1, IGFBP2, IGF2 and ANGPTL3 were applied on a cryopreserved umbilical cord blood mononuclear cell (UCB-MNC) ex vivo expansion system.
Clifford J Rosen - One of the best experts on this subject based on the ideXlab platform.
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estrogen stimulation of pleiotrophin enhances osteoblast differentiation and maintains bone mass in igfbp 2 null mice
Endocrinology, 2020Co-Authors: Victoria E Demambro, Clifford J Rosen, Susan Dcosta, Shalier K Xia, Zach C Cox, David R ClemmonsAbstract:Insulin-like growth factor binding protein-2 (IGFBP-2) stimulates osteoblast differentiation but only male IGFBP2 null mice have a skeletal phenotype. The trophic actions of IGFBP-2 in bone are mediated through its binding to receptor tyrosine phosphatase beta (RPTPβ). Another important ligand for RPTPβ is pleiotrophin (PTN), which also stimulates osteoblast differentiation. We determined the change in PTN and RPTPβ in IGFBP2-/- mice. Analysis of whole bone mRNA in wild-type and knockout mice revealed increased expression of Ptn. Rptpβ increased in gene-deleted animals with females having greater expression than males. Knockdown of PTN expression in osteoblasts in vitro inhibited differentiation, and addition of PTN to the incubation medium rescued the response. Estradiol stimulated PTN secretion and PTN knockdown blocked estradiol-stimulated differentiation. PTN addition to IGFBP-2 silenced osteoblast stimulated differentiation, and an anti-fibronectin-3 antibody, which inhibits PTN binding to RPTPβ, inhibited this response. Estrogen stimulated PTN secretion and downstream signaling in the IGFBP-2 silenced osteoblasts and these effects were inhibited with anti-fibronectin-3. Administration of estrogen to wild-type and IGFBP2-/- male mice stimulated an increase in both areal bone mineral density and trabecular bone volume fraction but the increase was significantly greater in the IGFBP2-/- animals. Estrogen also stimulated RPTPβ expression in the null mice. We conclude that loss of IGFBP-2 expression is accompanied by upregulation of PTN and RPTPβ expression in osteoblasts, that the degree of increase is greater in females due to estrogen secretion, and that this compensatory change may account for some component of the maintenance of normal bone mass in female mice.
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insulin like growth factor binding protein 2 is required for osteoclast differentiation
Journal of Bone and Mineral Research, 2012Co-Authors: Victoria E Demambro, Clifford J Rosen, Masanobu Kawai, Laura A Maile, Christine Wai, Teresa Cascella, David R ClemmonsAbstract:Global deletion of the IGFBP2 gene results in the suppression of bone turnover. To investigate the role of insulin-like growth factor-binding protein-2 (IGFBP-2) in regulating osteoclast differentiation, we cultured IGFBP2−/− bone marrow cells and found a reduction in the number of osteoclasts and impaired resorption. Addition of full-length IGFBP-2 restored osteoclast differentiation, fusion, and resorption. To determine the molecular domains of IGFBP-2 that were required for this effect to be manifest, IGFBP2−/− bone marrow cells were transfected with constructs in which the heparin-binding (HBD) or the IGF-binding domains of IGFBP-2 were mutated. We found that both domains were necessary for osteoclastogenesis because expression of the mutated forms of either domain failed to support the formation of functionally mature osteoclasts. To discern the mechanism by which IGFBP-2 regulates osteoclast formation, PTEN abundance and phosphorylation status as well as AKT responsiveness to IGF-I were analyzed. IGFBP2−/− cells had elevated levels of PTEN and phospho-PTEN compared with controls. Expression of wild-type IGFBP-2 reduced the level of PTEN to that of wild-type cells. Cells expressing the IGF-binding mutant showed suppression of PTEN and phospho-PTEN equivalent to the wild-type protein, whereas those expressing the IGFBP-2 HBD mutant showed no PTEN suppression. When the ability of IGF-I to stimulate AKT activation, measured by Thr308 and Ser473 phosphorylation, was analyzed, stimulation of Ser473 in response to IGF-I in preosteoclasts required the presence of intact IGFBP-2. This effect was duplicated by the addition of a CK2 inhibitor that prevents the phosphorylation of PTEN. In contrast, in fully differentiated osteoclasts, stimulation of Thr308 phosphorylation required the presence of intact IGFBP-2. We conclude that IGFBP-2 is an important regulator of osteoclastogenesis and that both the heparin- and the IGF-binding domains of IGFBP-2 are essential for the formation of fully differentiated and functional osteoclasts. © 2012 American Society for Bone and Mineral Research
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the heparin binding domain of igfbp 2 has insulin like growth factor binding independent biologic activity in the growing skeleton
Journal of Biological Chemistry, 2011Co-Authors: Masanobu Kawai, Victoria E Demambro, David R Clemmons, Mary L Bouxsein, Wesley G Beamer, Ernesto Canalis, Anne Breggia, Xinchun Shen, Clifford J RosenAbstract:Insulin-like growth factor-binding protein 2 (IGFBP-2) is a member of a family of six highly conserved IGFBPs that are carriers for the insulin-like growth factors (IGFs). IGFBP-2 levels rise during rapid neonatal growth and at the time of peak bone acquisition. In contrast, IGFBP2−/− mice have low bone mass accompanied by reduced osteoblast numbers, low bone formation rates, and increased PTEN expression. In the current study, we postulated that IGFBP-2 increased bone mass partly through the activity of its heparin-binding domain (HBD). We synthesized a HBD peptide specific for IGFBP-2 and demonstrated in vitro that it rescued the mineralization phenotype of IGFBP2−/− bone marrow stromal cells and calvarial osteoblasts. Consistent with its cellular actions, the HBD peptide ex vivo stimulated metacarpal periosteal expansion. Furthermore, administration of HBD peptide to IGFBP2−/− mice increased osteoblast number, suppressed marrow adipogenesis, restored trabecular bone mass, and reduced bone resorption. Skeletal rescue in the IGFBP2−/− mice was characterized by reduced PTEN expression followed by enhanced Akt phosphorylation in response to IGF-I and increased β-catenin signaling through two mechanisms: 1) stimulation of its cytosolic accumulation and 2) increased phosphorylation of serine 552. We conclude that the HBD peptide of IGFBP-2 has anabolic activity by activating IGF-I/Akt and β-catenin signaling pathways. These data support a growing body of evidence that IGFBP-2 is not just a transport protein but rather that it functions coordinately with IGF-I to stimulate growth and skeletal acquisition.
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gender specific changes in bone turnover and skeletal architecture in igfbp 2 null mice
Endocrinology, 2008Co-Authors: Victoria E Demambro, David R Clemmons, Lindsay G Horton, Mary L Bouxsein, Teresa L Wood, Wesley G Beamer, Ernesto Canalis, Clifford J RosenAbstract:IGF-binding protein-2 (IGFBP-2) is a 36-kDa protein that binds to the IGFs with high affinity. To determine its role in bone turnover, we compared IGFBP2−/− mice with IGFBP2+/+ colony controls. IGFBP2−/− males had shorter femurs and were heavier than controls but were not insulin resistant. Serum IGF-I levels in IGFBP2−/− mice were 10% higher than IGFBP2+/+ controls at 8 wk of age; in males, this was accompanied by a 3-fold increase in hepatic Igfbp3 and Igfbp5 mRNA transcripts compared with IGFBP2+/+ controls. The skeletal phenotype of the IGFBP2−/− mice was gender and compartment specific; IGFBP2−/− females had increased cortical thickness with a greater periosteal circumference compared with controls, whereas male IGFBP2−/− males had reduced cortical bone area and a 20% reduction in the trabecular bone volume fraction due to thinner trabeculae than IGFBP2+/+ controls. Serum osteocalcin levels were reduced by nearly 40% in IGFBP2−/− males, and in vitro, both CFU-ALP+ preosteoblasts, and tartrate-resistant acid phosphatase-positive osteoclasts were significantly less abundant than in IGFBP2+/+ male mice. Histomorphometry confirmed fewer osteoblasts and osteoclasts per bone perimeter and reduced bone formation in the IGFBP2−/− males. Lysates from both osteoblasts and osteoclasts in the IGFBP2−/− males had phosphatase and tensin homolog (PTEN) levels that were significantly higher than IGFBP2+/+ controls and were suppressed by addition of exogenous IGFBP-2. In summary, there are gender- and compartment-specific changes in IGFBP2−/− mice. IGFBP-2 may regulate bone turnover in both an IGF-I-dependent and -independent manner.
Philippe Monget - One of the best experts on this subject based on the ideXlab platform.
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the insulin like growth factor system a key determinant role in the growth and selection of ovarian follicles a comparative species study
Reproduction in Domestic Animals, 2003Co-Authors: Sabine Mazerbourg, Jian Zhou, C A Bondy, Philippe MongetAbstract:Contents The aim of the present paper is to make a comparative study of the expression of the elements of the insulin-like growth factor (IGF) system in different mammalian species and thus illuminate their potential role in the process of ovarian folliculogenesis in mammals. In most mammalian species, IGFs and IGFBPs (in particular IGFBP-2 and IGFBP-4) are considered, respectively, as stimulators and inhibitors of follicular growth and maturation. In mammalian species, IGFs might play a key role in sensitizing ovarian granulosa cells to FSH action during terminal follicular growth. Concentrations of IGFBP-2 and IGFBP-4 in follicular fluid strongly decrease and increase during follicular growth and atresia, respectively, leading to an increase and a decrease in IGF bioavailability, respectively. The decrease in these IGFBPs is because of a decrease in mRNA expression (IGFBP-2) and an increase in proteolytic degradation by PAPP-A in follicular fluid (IGFBP-2, IGFBP-4 and IGFBP-5), and likely participates in the selection of dominant follicles. In contrast, levels and/or sites of expression of IGF-I, IGF-II, IGFBP-4, IGFBP-5 and type II receptor in follicular cells strongly differ between mammalian species, suggesting that these phenomena might play species-specific or secondary roles in ovarian folliculogenesis.
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expression patterns of insulin like growth factor binding proteins 1 2 3 5 and 6 in the mid cycle monkey ovary
The Journal of Clinical Endocrinology and Metabolism, 2002Co-Authors: Jose A Arraztoa, Philippe Monget, Carolyn A Bondy, Jian ZhouAbstract:IGFs and IGF-binding proteins (IGFBPs) are thought to play important roles in ovarian follicular growth and selection. To elucidate the role of IGFBPs in primate ovarian function, we analyzed IGFBP mRNA expression patterns in ovaries from mid-cycle rhesus monkeys using in situ hybridization. IGFBP-1 mRNA was concentrated in theca-interstitial cells and was present at low levels in granulosa cells of atretic follicles. IGFBP-2 mRNA was expressed in the ovarian surface epithelium and granulosa cells of all antral follicles, including obviously atretic as well as dominant follicles. IGFBP-3 mRNA was localized in oocytes and in the ovarian vascular endothelium; this mRNA was also concentrated in the superficial cortical stroma in which it was distinctly more abundant in the nondominant ovary. Granulosa cells of mature dominant and ovulatory follicles selectively expressed IGFBP-5 mRNA. IGFBP-5 mRNA was also widely expressed in the ovarian stroma, in which, in contrast to IGFBP-3, it was distinctly more abundant in dominant, compared with nondominant, ovary. IGFBP-6 mRNA was present at low levels in the ovary interstitium and theca externa and was more abundant in the ovary surface epithelium. These novel data reveal distinctive cellular expression patterns for IGFBPs 1, 2, 3, 5, and 6 in the nonhuman primate ovary, suggesting distinct roles for each binding protein in ovarian function.
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insulin like growth factor binding proteins igfbps as potential physiological substrates for human kallikreins hk2 and hk3
FEBS Journal, 2001Co-Authors: Sophie Rehault, Roland R Tremblay, Sabine Mazerbourg, Ninette Gutman, Francis Gauthier, Philippe Monget, Thierry MoreauAbstract:Insulin-like growth factors (IGFs) are important growth regulators of both normal and malignant prostate cells. Their action is regulated by six insulin-like growth factor binding proteins (IGFBPs). The proteolytic cleavage of IGFBPs by various proteases decreases dramatically their affinity for their ligands and therefore enhances the bioavailability of IGFs. To elucidate the putative biological role of prostatic kallikreins hK2 and hK3 (prostate-specific antigen) in tumour progression, we analyzed the degradation of IGFBP-2, -3, -4 and -5 by these two tissue kallikreins. We found that hK3, already characterized as an IGFBP-3 degrading protease, cleaved IGFBP-4 but not IGFBP-2 and -5, whereas hK2 cleaved all of the IGFBPs much more effectively, and at concentrations far lower than those reported for other IGFBP-degrading proteases. The proteolytic patterns after cleavage of IGFBPs by hK2 and hK3 were similar and were not modified in the presence of IGF-I. Heparin, but not other glycosaminoglycans, enhanced dramatically the ability of hK3 but not hK2 to degrade IGFBP-3 and IGFBP-4. More importantly, the IGFBP fragments generated by hK2 and hK3 had no IGF-binding capacity, as assessed by Western ligand blotting. Our results suggest that the prostatic kallikreins hK2 and hK3 may influence specifically the tumoral growth of prostate cells through the degradation of IGFBPs, to increase IGF bioavailability.
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expression of messenger ribonucleic acids of insulin like growth factor binding protein 2 4 and 5 in the ovine ovary localization and changes during growth and atresia of antral follicles
Biology of Reproduction, 1996Co-Authors: Nathalie Besnard, Claudine Pisselet, D Monniaux, A Locatelli, Francis Benne, Francois Gasser, Francois Hatey, Philippe MongetAbstract:In the sheep as in many mammalian species, growth and atresia of antral follicles are characterized, respectively, by a decrease and a high increase in the intrafollicular levels of insulinlike growth factor binding proteins of less than 40 kDa (IGFBPs < 40 kDa), mainly IGFBP-2, -4, and -5. The objective of this study was to investigate whether such changes are associated with changes in follicular expression of the corresponding mRNA. For this purpose, ovaries were recovered from ewes slaughtered at the end of follicular phase (i.e., 30 h after progestagen sponge removal; control ewes) or at 24 h, 36 h, or 72 h after hypophysectomy (hypox) performed 30 h after sponge removal. The expression of mRNA of IGFBPs of less than 40 kDa (IGFBPs < 40 kDA mRNA) was studied in ovine antral follicles from control and hypox ewes by in situ hybridization using PsS]labeled human IGFBP-2, -4, and -5 cRNA as probes. In control ewes, IGFBP-2 mRNA was mainly expressed in granulosa as a gradient in healthy follicles, the expression being higher in granulosa cells close to the basal membrane than in granulosa cells bordering the antrum and within the cumulus. The level of IGFBP-2 mRNA was lower both in granulosa cells close to the basal membrane and in those bordering the antrum from small follicles than in the corresponding compartments of granulosa cells from large healthy follicles (p < 0.05). In healthy follicles, IGFBP-4 and -5 mRNA were mainly expressed in thecal cells. No change in level of IGFBP-4 mRNA was observed between small and large follicles, whereas the level of IGFBP-5 mRNA tended to be lower in thecal cells from large compared to small follicles (p = 0.055). In atretic follicles, expression of IGFBPs < 40 kDa mRNA strongly increased in granulosa (IGFBP-2 and -5, p < 0.01) and in thecal cells (IGFBP-2 and -4, p < 0.01). In hypox ewes, the chronology of changes in expression of follicular IGFBPs < 40 kDa mRNA and in intrafollicular levels of the corresponding proteins was studied during atresia of large antral follicles. Early atresia of large follicles was associated with a strong decrease in intrafollicular estradiol levels (p < 0.001); an increase in intrafollicular levels of IGFBP-2, -4, and -5 (p < 0.001); an increase in both IGFBP-2 (p < 0.001) and -5 (p < 0.01) mRNA expression in granulosa and thecal cells; but no change in IGFBP-4 mRNA expression. Late atresia of large follicles was associated with a further decrease in intrafollicular estradiol levels (p < 0.001); a further increase in intrafollicular levels of IGFBP-2, -4, and -5 (p < 0.001); an increase in IGFBP-4 (p < 0.01) and -5 (p < 0.05) mRNA expression in theca and granulosa, respectively; a decrease in IGFBP-5 mRNA expression in theca (p < 0.05); but no further increase in IGFBP-2 mRNA expression.
