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  • 1
    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.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 68 (1998), S. 446-456 
    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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  • 3
    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.
    Type of Medium: Electronic Resource
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