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- Pardali, E, et al.
(författare)
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Smad and AML proteins synergistically confer transforming growth factor beta1 responsiveness to human germ-line IgA genes.
- 2000
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 275:5, s. 3552-60
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Tidskriftsartikel (refereegranskat)abstract
- Transcription of germ-line immunoglobulin heavy chain genes conditions them to participate in isotype switch recombination. Transforming growth factor-beta1 (TGF-beta1) stimulates promoter elements located upstream of the IgA1 and IgA2 switch regions, designated Ialpha1 and Ialpha2, and contributes to the development of IgA responses. We demonstrate that intracellular Smad proteins mediate activation of the Ialpha1 promoter by TGF-beta. TGF-beta type 1 receptor (ALK-5), activin type IB receptor (ALK-4), and the "orphan" ALK-7 trans-activate the Ialpha1 promoter, thus raising the possibility that other members of the TGF-beta superfamily can also modulate IgA synthesis. Smads physically interact with the AML family of transcription factors and cooperate with them to activate the Ialpha1 promoter. The Ialpha1 element provides a canapé of interspersed high and low affinity sites for Smad and AML factors, some of which are indispensable for TGF-beta responsiveness. While AML.Smad complexes are formed in the cytoplasm of DG75 and K562 cells constitutively, only after TGF-beta receptor activation, novel Smad3.Smad4.AML complexes are detected in nuclear extracts by EMSA with Ialpha1 promoter-derived probes. Considering the wide range of biological phenomena that AMLs and Smads regulate, the physical/functional interplay between them has implications that extend beyond the regulation of class switching to IgA.
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| 3. |
- Brattsand, G, et al.
(författare)
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Quantitative analysis of the expression and regulation of an activation-regulated phosphoprotein (oncoprotein 18) in normal and neoplastic cells.
- 1993
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Ingår i: Leukemia. - 0887-6924 .- 1476-5551. ; 7:4, s. 569-79
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Tidskriftsartikel (refereegranskat)abstract
- Activation of protein kinase C results in phosphorylation of a 19-kDa protein termed 19K. Isolation and sequence analysis of a cDNA encoding the 19K protein revealed that this protein has been studied in other systems under different names. The name oncoprotein 18 (Op18) has been proposed on the basis of a postulated up-regulation in neoplastic cells. In the present report we adopt the designation Op18 for the 19K protein, and quantify this phosphoprotein in a series of leukemia/lymphoma cell lines, a panel of non-transformed cells and some terminally differentiated cell types. For this purpose we have developed reagents allowing quantitative Western-blot analysis, and quantification of Op18 on the single cell level by flow cytometric analysis. The data demonstrates a pronounced up-regulation of the Op18 protein in most leukemia/lymphoma cell lines. The HPB-ALL cell line provided the most extreme case and expressed 7 x 10(6) Op18 molecules/cell, which compares with 0.65 x 10(6) Op18 molecules/cell in non-transformed lymphoblastoid cells. The expression of Op18 appears to be restricted to cell types with proliferative potential, but it is clear from our results that up-regulation of Op18 is uncoupled from cellular proliferation. Moreover, by employing an Epstein-Barr virus based shuttle vector, we expressed Op18 cDNA in lymphoblastoid cells. This resulted in a three to fourfold up-regulation of Op18 that did not have any detectable consequences for cell-surface phenotype or cell size. However, increased expression of Op18 resulted in a partial inhibition of cell proliferation. Taken altogether, the results suggest that up-regulation Op18 levels in leukemia/lymphoma cells are strongly associated with, but not a direct cause of tumour progression.
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| 4. |
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| 5. |
- Goumans, MJ, et al.
(författare)
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Balancing the activation state of the endothelium via two distinct TGF-beta type I receptors
- 2002
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Ingår i: EMBO Journal. - : Wiley. - 1460-2075. ; 21:7, s. 1743-1753
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Tidskriftsartikel (refereegranskat)abstract
- The generation of mice lacking specific components of the transforming growth factor-beta (TGF-beta) signal tranduction pathway shows that TGF-beta is a key player in the development and physiology of the cardiovascular system. Both pro- and anti-angiogenic properties have been ascribed to TGF-beta, for which the molecular mechanisms are unclear. Here we report that TGF-beta can activate two distinct type I receptor/Smad signalling pathways with opposite effects. TGF-beta induces phosphorylation of Smad1/5 and Smad2 in endothelial cells and these effects can be blocked upon selective inhibition of ALK1 or ALK5 expression, respectively. Whereas the TGF-beta/ALK5 pathway leads to inhibition of cell migration and proliferation, the TGF-beta/ ALK1 pathway induces endothelial cell migration and proliferation. We identified genes that are induced specifically by TGF-beta-mediated ALK1 or ALK5 activation. Id1 was found to mediate the TGF-beta/ALK1-induced (and Smad-dependent) migration, while induction of plasminogen activator inhibitor-1 by activated ALK5 may contribute to the TGF-beta-induced maturation of blood vessels. Our results suggest that TGF-beta regulates the activation state of the endothelium via a fine balance between ALK5 and ALK1 signalling.
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| 10. |
- Rosendahl, A, et al.
(författare)
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Transforming growth factor-beta- and Activin-Smad signaling pathways are activated at distinct maturation stages of the thymopoeisis
- 2003
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Ingår i: International Immunology. - : Oxford University Press (OUP). - 1460-2377. ; 15:12, s. 1401-1414
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Tidskriftsartikel (refereegranskat)abstract
- Members of the transforming growth factor (TGF)-beta family play pivotal roles in the control of differentiation, proliferation and tolerance in peripheral T cells. Recently, they have been implicated in thymic selection, but their role is so far not well characterized. In the present study, we demonstrate that specific thymocyte populations are under the influence of either the TGF-beta and/or Activin pathway, and transduce signals into the nucleus via phosphorylated Smad2 (pSmad2). Thymocytes in the medulla and in the subcapsular zone expressed nuclear translocated pSmad2, a hallmark of active TGF-beta/Activin receptor signaling. When analyzed at the cellular level, the pSmad2(+) cells were confined to the double-negative (DN) and single-positive (SP) subpopulations. Moreover, the most immature DN thymocytes (CD44(+)CD25(-) and CD44(+)CD25(+)) expressed higher levels of pSmad2 compared to the more mature DN. In vitro stimulation demonstrated that pure CD44(+)CD25(-), CD44(+)CD25(+) and CD44(+)CD25(+) thymocytes respond to ActivinA, while the mature CD4(+) and CD8(+) SP thymocytes respond to TGF-beta stimulation measured as enhanced phosphorylation of Smad2. Double staining of pSmad2(+) cells with either the Activin type I receptor, ALK4, or the TGF-beta type I receptor, ALK5, demonstrated that pSmad2(+) DN cells exhibited high levels of immunoreactivity to ALK4 and moderate levels of immunoreactivity to the TGF-beta-responsive ALK5 receptor. In sharp contrast, the SP pSmad2(+) cells were predominately ALK5(+). Collectively, our results demonstrate that early and late thymocytes express pSmad2 in the nuclei in vivo. The functional experiments in vitro suggest that members of the TGF-beta family (TGF-beta or Activin) may play important non-redundant roles during different stages of thymopoiesis.
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