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Transforming Growth Factor β1 Induces Nuclear Export of Inhibitory Smad7
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Medicinska och farmaceutiska vetenskapsområdet, centrumbildningar mm , Ludwig Institute for Cancer Research.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Medicinska och farmaceutiska vetenskapsområdet, centrumbildningar mm , Ludwig Institute for Cancer Research.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Genetics and Pathology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Medicinska och farmaceutiska vetenskapsområdet, centrumbildningar mm , Ludwig Institute for Cancer Research.
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1998 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, ., Vol. 273, no 44, 29195-29201 p.Article in journal (Refereed) Published
Abstract [en]

Transforming growth factor beta (TGF-beta) signals from membrane to nucleus through serine/threonine kinase receptors and their downstream effector molecules, termed Smad proteins. Recently, Smad6 and Smad7 were identified, which antagonize TGF-beta family signaling by preventing the activation of signal-transducing Smad complexes. Here we report that Smad7, but not Smad6, inhibits TGF-beta1-induced growth inhibition and the expression of immediate early response genes, including Smad7. Interestingly, in the absence of ligand, Smad7 was found to be predominantly localized in the nucleus, whereas Smad7 accumulated in the cytoplasm upon TGF-beta receptor activation. The latter is in accordance with the physical association of Smad7 with the ligand-activated TGF-beta receptor complex in the cell membrane. Whereas the ectopically expressed C-terminal domain of Smad7 was also exported from the nucleus to the cytoplasm upon TGF-beta challenge, a Smad7 mutant with a small deletion at the C terminus or only the N-terminal domain of Smad7 was localized mainly in the cytoplasm in the absence or presence of ligand. This suggests that an intact Mad homology 2 domain is important for nuclear localization of Smad7. The nuclear localization of Smad7 suggests a functional role distinct from its antagonistic effect in receptor-mediated Smad activation.

Place, publisher, year, edition, pages
1998. Vol. 273, no 44, 29195-29201 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-90978DOI: 10.1074/jbc.273.44.29195PubMedID: 9786930OAI: oai:DiVA.org:uu-90978DiVA: diva2:163526
Available from: 2003-10-20 Created: 2003-10-20 Last updated: 2009-10-06Bibliographically approved
In thesis
1. Regulation of TGF-β/Smad Signaling Through Smad Interacting Proteins
Open this publication in new window or tab >>Regulation of TGF-β/Smad Signaling Through Smad Interacting Proteins
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Transforming growth factor-β (TGF-β) superfamily members are multi-functional regulators of cell fate. These factors signal by binding to a limited number of highly conserved transmembrane type I and type II serine/threonine kinase receptors. These receptors initiate signals into the cell via the Smad proteins. Up to date, 8 different mammalian Smads are reported and are divided into three subgroups; receptor regulated Smads (R-Smads), common mediator Smads (Co-Smads) and inhibitory Smads (I-Smads). This thesis investigates the function and regulation of TGF-β/Smad signaling through identification and characterization of Smad interacting proteins.

I-Smads, i.e. Smad6 and Smad7, are potent antagonists of the TGF-β superfamily signaling. We found that Smad7, but not Smad6, inhibits TGF-β1-induced growth inhibition and expression of immediate early response genes. Interestingly, in the absence of ligand, Smad7 was found to be predominantly localized in the nucleus, whereas Smad7 accumulated in the cytoplasm upon TGF-β receptor activation. Moreover, we found that the MH2 domain is important for nuclear export.

To investigate further the role of inhibitory Smads, we have identified AMSH as a Smad6 interacting protein using a yeast two-hybrid screening method. AMSH was previously discovered as the associated molecule with the SH3 domain of STAM. AMSH interacts with I-Smads, but not with R- and Co-Smads upon receptor activation and potentiates BMP-induced activation of transcriptional reporter activity, growth arrest and apoptosis. AMSH was found to prevent Smad6 from binding to activated type I receptors and/or activated R-Smads. Smad anchor for receptor activation (SARA) is critical for Smad2 and Smad3 activation by TGF-β receptors. The present studies show that the localization of SARA in early endosomes is regulated through its FYVE domain. We have found that the FYVE domain of SARA is sufficient and necessary for the early endosomal localization, probably through its interaction with PtdIns(3)P. Moreover, the localization of SARA in early endosomes is required for efficient TGF-β/Smad signaling.

Both Notch and BMP signaling pathways are important for vascular development. We have found that Herp2, which is originally known as one of the Notch target genes, is synergistically induced upon activation of Notch and BMP signaling pathways in endothelial cells (ECs). The critical elements for synergistical activation of Herp2 gene by BMP and Notch pathway were identified. Furthermore, the Notch intracellular domain interacts with Smad5 upon BMP receptor and this interaction becomes stronger in the presence of pCAF. Interestingly, Herp2 was found to antagonize BMP receptor- or Id-mediated EC migration.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 55 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 0282-7476 ; 1296
Keyword
Cell and molecular biology, Cell- och molekylärbiologi
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:uu:diva-3690 (URN)91-554-5772-X (ISBN)
Public defence
2003-11-10, C8:301, BMC, Uppsala, 09:15
Opponent
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Available from: 2003-10-20 Created: 2003-10-20Bibliographically approved

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