Itoh S, Ericsson J, Nishikawa J, Heldin C H, ten Dijke P
The Netherlands Cancer Institute, Division of Cellular Biochemistry, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Nucleic Acids Res. 2000 Nov 1;28(21):4291-8. doi: 10.1093/nar/28.21.4291.
Smads perform pivotal functions in the intracellular signaling of transforming growth factor-beta (TGF-beta). TGF-beta-mediated activation of TGF-beta type I receptor stimulates the phosphorylation of Smad2 and Smad3 and subsequent heteromeric complex formation with Smad4. The heteromeric Smad complexes translocate into the nucleus where they, in co-operation with co-activators and co-repressors, regulate transcriptional responses. Here we investigated the possible co-activator function of P/CAF in TGF-beta/Smad signaling. P/CAF was found to interact directly with Smad3 in vitro. Moreover, Smad2 and Smad3 interacted with P/CAF upon TGF-beta type I receptor activation in cultured mammalian cells. The interaction involves the MH2 domain of Smad3 and the N-terminal region of P/CAF. P/CAF potentiated the transcriptional activity of heterologous Gal4-Smad2 and Gal4-Smad3 fusion proteins. In addition, P/CAF potentiated the TGF-beta/Smad3-induced transcriptional responses, which could be further enhanced by co-activators p300 and Smad4. P/CAF may, therefore, activate Smad-mediated transcriptional responses independently or in co-operation with p300/CBP. Our results indicate a direct physical and functional interplay between two negative regulators of cell proliferation, Smad3 and P/CAF.
Smads在转化生长因子-β（TGF-β）的细胞内信号传导中发挥关键作用。TGF-β介导的TGF-β I型受体激活刺激Smad2和Smad3的磷酸化以及随后与Smad4形成异源复合物。异源Smad复合物转运到细胞核中，在那里它们与共激活因子和共抑制因子合作调节转录反应。在此，我们研究了P/CAF在TGF-β/Smad信号传导中可能的共激活因子功能。发现P/CAF在体外直接与Smad3相互作用。此外，在培养的哺乳动物细胞中，TGF-β I型受体激活后，Smad2和Smad3与P/CAF相互作用。这种相互作用涉及Smad3的MH2结构域和P/CAF的N端区域。P/CAF增强了异源Gal4-Smad2和Gal4-Smad3融合蛋白的转录活性。此外，P/CAF增强了TGF-β/Smad3诱导的转录反应，共激活因子p300和Smad4可进一步增强该反应。因此，P/CAF可能独立地或与p300/CBP合作激活Smad介导的转录反应。我们的结果表明细胞增殖的两个负调节因子Smad3和P/CAF之间存在直接的物理和功能相互作用。
