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  • 1
    ISSN: 0730-2312
    Keywords: IGF-I ; IGF-II ; cAMP ; PKA ; PKC ; prostaglandin ; osteoblasts ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Bone cells synthesize and respond to IGF-I and IGF-II which contribute to bone remodeling and linear growth. In osteoblasts, prostaglandin (PG)E2 stimulates IGF-I but not IGF-II synthesis through a cAMP-dependent protein kinase A (PKA)-related event. However, protein kinase C (PKC) activation by PGE2 enhances replication and protein synthesis by less differentiated periosteal cells more so than in osteoblast-enriched cultures from fetal rat bone. Using various PGs and other PKA and PKC pathway activators, the importance of these aspects of PGE2 activity has now been examined on IGF receptors in these bone cell culture models. PGE2 and other agents that activate PKA enhanced 125I-IGF-II binding to type 2 IGF receptors on both cell populations. In contrast, agents that activate PKC enhanced 125I-IGF-I binding to type 1 receptors on less differentiated bone cells, and of these, only phorbol myristate acetate (PMA), which activates PKC in a receptor-independent way, was effective in osteoblast-enriched cultures. No stimulator increased total type 1 receptor protein in either cell population. Consequently, ligand binding to type 1 and type 2 IGF receptors is differentially modulated by specific intracellular pathways in bone cells. Importantly, changes in apparent type 1 receptor number occur rapidly and may do so at least in part through post-translational effects. These results may help to predict new ways to manipulate autocrine or paracrine actions by IGFs in skeletal tissue. J. Cell. Biochem. 68:446-456, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 13 Ill.
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  • 2
    ISSN: 0730-2312
    Keywords: IGFBP ; cAMP ; PKA ; prostaglandin ; bone ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Insulin-like growth factor (IGF)-I and IGF-II are expressed at biologically effective levels by bone cells. Their stability and activity are modulated by coexpression of IGF binding proteins (IGFBPs). Secreted IGFBPs may partition to soluble, cell-associated, and matrix-bound compartments. Extracellular localization may sequester, store, or present IGFs to appropriate receptors. Of the six IGFBPs known, rat osteoblasts synthesize all but IGFBP-1. Of these, IGFBP-3, -4, and -5 mRNAs are induced by an increase in cAMP. Little is known about extracellular IGFBP localization in bone and nothing about IGFBP expression by nonosteoblastic periosteal bone cells. We compared basal IGFBP expression in periosteal and osteoblast bone cell cultures and assessed the effects of changes in cAMP-dependent protein kinase A or protein kinase C. Basal IGFBP gene expression differed principally in that more IGFBP-2 and -5 occurred in osteoblast cultures, and more IGFBP-3 and -6 occurred in periosteal cultures. An increase in cAMP enhanced IGFBP-3, -4, and -5 mRNA and accordingly increased soluble IGFBP-3, -4, and -5 and matrix-bound IGFBP-3 and -5 in both bone cell populations. In contrast, protein kinase C activators suppressed IGFBP-5 mRNA, and its basal protein levels remained very low. We also detected low Mr bands reactive with antisera to IGFBP-2, -3, and -5, suggesting proteolytic processing or degradation. Our studies reveal that various bone cell populations secrete and bind IGFBPs in selective ways. Importantly, inhibitory IGFBP-4 does not significantly accumulate in cell-associated compartments, even though its secretion is enhanced by cAMP. Because IGFBPs bind IGFs less tightly in cell-bound compartments, they may prolong anabolic effects by agents that increase bone cell cAMP. J. Cell. Biochem. 71:351-362, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0730-2312
    Keywords: transforming growth factor β (TGF-β) ; collagen ; receptors ; gene promoters ; osteogenesis ; metabolic bone diseases ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Glucocorticoid in excess produces bone loss in vivo. Consistent with this, it reduces the stimulatory effect of transforming growth factor β (TGF-β) on collagen synthesis in osteoblast-enriched cultures in vitro, where it also suppresses TGF-β binding to its type I receptors. Analogous studies with bone morphogenetic protein-2 (BMP-2) show directly opposite results. These findings prompted us to assess the effect of glucocorticoid on BMP-2 activity in cultured bone cells, and whether either agent had a dominant influence on TGF-β binding or function. BMP-2 activity was retained in part in osteoblast-enriched cultures pre-treated or co-treated with cortisol, and was fully evident when glucocorticoid exposure followed BMP-2 treatment. In addition, BMP-2 suppressed the effects of cortisol on TGF-β activity, on TGF-β binding, and on gene promoter activity directed by a glucocorticoid sensitive transfection construct. While BMP-2 also alters the function of less-differentiated bone cells, it only minimally prevented cortisol activity in these cultures. Our studies indicate that BMP-2 can oppose certain effects by cortisol on differentiated osteoblasts, and may reveal useful ways to diminish glucocorticoid-dependent bone wasting. J. Cell. Biochem. 67:528-540, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 4
    ISSN: 0730-2312
    Keywords: AML/CBF/PEBP2 ; CBFa1 ; differentiation ; osteoblasts ; regulatory elements ; transforming growth factor-β ; receptor ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Organization of the transforming growth factor-β (TGF-β) type I receptor (TRI) promoter predicts constitutive transcription, although its activity increases with differentiation status in cultured osteoblasts. Several sequences in the rat TRI promoter comprise cis-acting elements for CBFa (AML/PEBP2α) transcription factors. By gel mobility shift and immunological analyses, a principal osteoblast-derived nuclear factor that binds to these sites is CBFa1(AML-3/PEBP2αA). Rat CBFa1 levels parallel expression of the osteoblast phenotype and increase under conditions that promote mineralized bone nodule formation in vitro. Fusion of CBFa binding sequence from the TRI promoter to enhancer-free transfection vector increases reporter gene expression in cells that possess abundant CBFa1, and overexpression of CBFa increase the activity of transfected native TRI promoter/reporter plasmid. Consequently, phenotype-restricted use of cis-acting elements for CBFa transcription factors can contribute to the high levels of TRI that parallel osteoblast differentiation and to the potent effects of TGF-β on osteoblast function. J. Cell. Biochem. 69:353-363. © 1998 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 5
    ISSN: 0730-2312
    Keywords: transcription initiation ; CpG island ; transcription factor AP2 ; transcription factor Sp1 ; osteoblasts ; differentiation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Transforming growth factor (TGF-β) binds several discrete membrane proteins. Of these, a type I receptor appears indispensable for signal transduction. Previous examination of TGF-β receptor expression has been limited to changes in cell surface protein, and more recently, mRNA abundance. In order to learn more about TGF-β function and receptor expression during osteogenesis, we have now cloned a 4 kilobase (kb) DNA fragment 5' proximal to the coding region of the rat TGF-β type I receptor gene. Sequence analysis revealed multiple elements compatible with transcription initiation, including a properly positioned and oriented CCAAT box, six Sp1 binding sites (three defining GC boxes), and two strong AP2 binding sites within a 0.7 kb span directly upstream of the coding region. The 3' terminal 0.3 kb span comprises a GC-enriched (77%) so-called CpG island that, like other similarly organized promoters, lacks a TATA box. Primer extension and RNase protection studies with cRNAs from this area show multiple initiation sites within 220 bp 5' proximal to the initial methionine codon. Transient transfections using nested, deleted, and inverted promoter sequences demonstrated maximal reporter expression by a 1 kb fragment encompassing all of these elements. Truncation of the 1 kb fragment from the 5' and 3' ends indicated the need for several elements for peak promoter activity. These results, and transfections in fetal rat bone and dermal cells, suggest that this promoter contains elements that specify basal and conditional expression of the TGF-β type I receptor in bone. © 1996 Wiley-Liss, Inc.
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  • 6
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Primary osteoblast-enriched (Ob) cultures from fetal rat bone synthesize insulinlike growth factor (IGF) I and IGF-II, which each enhance Ob function. While a number of agents modulate IGF-I production, IGF-II is constitutively expressed in this culture model. Independent of their expression, however, the activity of the IGFs can be modified by a small group of proteins termed IGF binding proteins (IGFBPs), but little is known about the regulation of individual IGFBPs that are synthesized by Ob cells. Northern blot analysis revealed that serum-deprived primary rat Ob cells. Northern blot analysis revealed that serum-deprived primary rat Ob cells express transcripts encoding IGFBP-2, IGFBP-3, IGFBP-4, IGFBP-5, and IGFBP-6, but undetectable levels of IGFBP-1 transcripts. Western ligand blots of Ob culture medium probed with 125I-IGF-I or 125I-IGF-II showed predominant IGFBPs migrating at 30/32 kDa, with minor bands at 24 and 38-47 kDa. Western antibody analysis identified IGFBP-2 and IGFBP-5 within the 30/32 kDa complex, while gel mobility shift on SDS-PAGE following deglycosylation determined that IGFBP-3 comprised the 38-47 kDa complex. By Northern analysis, 6 h treatment with prostaglandin E2 (PGE2), growth hormone (hGH), IGF-I, or IGF-II revealed a complex pattern of regulatory effects on steady-state IGFBP transcript expression. PGE2 increased the transcript levels of IGFBP-3, IGFBP-4, and IGFBP-5, (∼22-, ∼2-, and ∼4-fold respectively), but had no effect on IGFBP-2 or IGFBP-6 transcripts. hGH enhanced IGFBP-3 and IGFBP-5 transcripts (each approximately twofold). IGF-I and IGF-II had no effect on IGFBP-2 steady-state transcript levels but enhanced the level of IGFBP-5 transcripts (approximately fourfold). By Western ligand blot analysis, 24 h treatment with PGE2 elevated the 24 and 38-47 kDa IGFBPs and to a lesser extent the 30/32 kDa complex, hGH elevated the 38-47 kDa IGFBPs, and IGF-I and IGF-II each increased the 30/32 kDa IGFBP complex. Therefore, a comparison of results obtained from Northern, Western ligand, and Western antibody studies indicates that multiple IGFBPs are expressed by primary rat Ob cultures. While IGFBP-2 and IGFBP-6 synthesis in Ob cultures is relatively unaffected by short-term treatment with PGE2, hGH, or the IGFs, these agents modify IGFBP-3, IGFBP-4, and IGFBP-5 expression with individual patterns of effects. In addition, some changes in IGFBP polypeptide levels that are independent of alterations in transcript expression may result from the formation of complexes between IGFs and certain IGFBPs, which could serve to store IGFs for future utilization in the formation phase of bone remodeling. © 1994 Wiley-Liss, Inc.
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  • 7
    Publication Date: 2014-02-28
    Description: A competitive enzyme-linked immunosorbent assay (cELISA) was developed by using a whole-cell antigen from a marine Brucella sp. isolated from a harbor seal (Phoca vitulina). The assay was designed to screen sera from multiple marine mammal species for the presence of antibodies against marine-origin Brucella. Based on comparisons with culture-confirmed cases, specificity and sensitivity for cetacean samples tested were 73% and 100%, respectively. For pinniped samples, specificity and sensitivity values were 77% and 67%, respectively. Hawaiian monk seal (Monachus schauinslandi; n = 28) and bottlenose dolphin (Tursiops truncatus; n = 48) serum samples were tested, and the results were compared with several other assays designed to detect Brucella abortus antibodies. The comparison testing revealed the marine-origin cELISA to be more sensitive than the B. abortus tests by the detection of additional positive serum samples. The newly developed cELISA is an effective serologic method for detection of the presence of antibodies against marine-origin Brucella sp. in marine mammals.
    Keywords: Chemistry ; Fisheries ; Management
    Repository Name: Aquatic Commons
    Type: Article , PeerReviewed
    Format: application/pdf
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