| 1. |
- Giandomenico, Valeria, et al.
(författare)
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Coactivator-dependent acetylation stabilizes members of the SREBP family of transcription factors
- 2003
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Ingår i: Molecular and Cellular Biology. - 0270-7306 .- 1098-5549. ; 23:7, s. 2587-2599
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Tidskriftsartikel (refereegranskat)abstract
- Members of the SREBP family of transcription factors control cholesterol and lipid homeostasis and play important roles during adipocyte differentiation. The transcriptional activity of SREBPs is dependent on the coactivators p300 and CBP. We now present evidence that SREBPs are acetylated by the intrinsic acetyltransferase activity of p300 and CBP. In SREBP1a, the acetylated lysine residue resides in the DNA-binding domain of the protein. Coexpression with p300 dramatically increases the expression of both SREBP1a and SREBP2, and this effect is dependent on the acetyltransferase activity of p300, indicating that acetylation of SREBPs regulates their stability. Indeed, acetylation or mutation of the acetylated lysine residue in SREBP1a stabilizes the protein. We demonstrate that the acetylated residue in SREBP1a is also targeted by ubiquitination and that acetylation inhibits this process. Thus, our studies define acetylation-dependent stabilization of transcription factors as a novel mechanism for coactivators to regulate gene expression.
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| 2. |
- Simonsson, Maria, 1976-
(författare)
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Protein Acetylation – A Multifunctional Regulator of TGF-β Signaling
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transforming growth factor β (TGF-β) is a member of a large family of cytokines that regulate many crucial events in cells, including proliferation, differentiation, migration and apoptosis. Deregulated TGF-β signaling is associated with various forms of cancers and developmental disorders. TGF-β binds to a receptor complex at the surface of cells and activates a signaling cascade involving specific intracellular signaling proteins, known as Smads. Following receptor activation, the Smads are activated by phosphorylation and translocate to the nucleus, where they activate or repress the expression of specific genes. Posttranslational modifications regulate the function of proteins in a number of ways, including their activity, stability, localization, and/or interactions with other proteins. These modifications are important to modulate the strength and specificity of cellular signal transduction. Smad7, an important negative modulator of TGF-β signaling, has been shown to be acetylated by the acetyltransferase p300. My aim was to further explore the involvement of protein acetylation in TGF-β-dependent signaling. We could show that the acetylation of Smad7 is a reversible process. Interestingly, earlier work had shown that the acetylation of Smad7 prevented its degradation. In agreement with this observation, we found that the ubiquitylation and degradation of Smad7 was increased following cotransfection with HDAC1, a protein deacetylase. Based on our observations, we propose a model in which the stability of Smad7 is controlled by the balance between its acetylation, deacetylation and ubiquitylation. In a separate study, we found that also Smad2 and Smad3 are acetylated by p300/CBP and P/CAF upon TGF-β stimulation. Moreover, we found that the acetylation of the short isoform of Smad2 promoted its DNA binding activity, resulting in an increased transcriptional activity. Our results suggest that the increased DNA binding in response to acetylation is due to a conformational change in Smad2.
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| 3. |
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| 4. |
- Simonsson, Maria, et al.
(författare)
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The balance between acetylation and deacetylation controls Smad7 stability
- 2005
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Ingår i: Journal of Biological Chemistry. - : American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 280:23, s. 21797-21803
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Tidskriftsartikel (refereegranskat)abstract
- Transforming growth factor beta (TGFbeta) regulates multiple cellular processes via activation of Smad signaling pathways. We have recently demonstrated that the inhibitory Smad7 interacts with the acetyl transferase p300 and that p300 acetylates Smad7 on two lysine residues. These lysine residues are critical for Smurf-mediated ubiquitination of Smad7, and acetylation protects Smad7 from TGFbeta-induced degradation. In this study we demonstrate that Smad7 interacts with specific histone deacetylases (HDACs) and that the same HDACs are able to deacetylate Smad7. The interaction with HDACs is dependent on the C-terminal MH2 domain of Smad7. In addition, HDAC1-mediated deacetylation of Smad7 decreases the stability of Smad7 by enhancing its ubiquitination. Thus, our results demonstrate that the degradation of Smad7 is regulated by the balance between acetylation, deacetylation and ubiquitination, indicating that this could be a general mechanism to regulate the stability of cellular proteins.
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| 5. |
- Simonsson, Maria, et al.
(författare)
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The DNA Binding Activities of Smad2 and Smad3 Are Regulated by Coactivator-mediated Acetylation
- 2006
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 281:52, s. 39870-39880
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorylation-dependent activation of the transcription factors Smad2 and Smad3 plays an important role in TGFbeta-dependent signal transduction. Following phosphorylation of Smad2 and Smad3, these molecules are translocated to the nucleus where they interact with coactivators and/or corepressors, including p300, CBP, and P/CAF, and regulate the expression of TGFbeta target genes. In the current study, we demonstrate that both Smad2 and Smad3 are acetylated by the coactivators p300 and CBP in a TGFbeta-dependent manner. Smad2 is also acetylated by P/CAF. The acetylation of Smad2 was significantly higher than that of Smad3. Lys(19) in the MH1 domain was identified as the major acetylated residue in both the long and short isoform of Smad2. Mutation of Lys(19) also reduced the p300-mediated acetylation of Smad3. By generating acetyl-Lys(19)-specific antibodies, we demonstrate that endogenous Smad2 is acetylated on this residue in response to TGFbeta signaling. Acetylation of the short isoform of Smad2 improves its DNA binding activity in vitro and enhances its association with target promoters in vivo, thereby augmenting its transcriptional activity. Acetylation of Lys(19) also enhanced the DNA binding activity of Smad3. Our data indicate that acetylation of Lys(19) induces a conformational change in the MH1 domain of the short isoform of Smad2, thereby making its DNA binding domain accessible for interactions with DNA. Thus, coactivator-mediated acetylation of receptor-activated Smad molecules could represent a novel way to regulate TGFbeta signaling.
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