Sun Yan, Ding Lihua, Zhang Hao, Han Juqiang, Yang Xiao, Yan Jinghua, Zhu Yunfeng, Li Jiezhi, Song Haifeng, Ye Qinong
Beijing Institute of Biotechnology, Beijing, 100850 People's Republic of China.
Nucleic Acids Res. 2006;34(21):6314-26. doi: 10.1093/nar/gkl914. Epub 2006 Nov 11.
Smad2, Smad3 and Smad4 proteins are considered to be key mediators of transforming growth factor-beta (TGF-beta) signaling. However, the identities of the Smad partners mediating TGF-beta signaling are not fully understood. Here, we show that RNA-binding protein with multiple splicing (RBPMS), a member of the RNA-binding protein family, physically interacts with Smad2, Smad3 and Smad4 both in vitro and in vivo. The presence of TGF-beta increases the binding of RBPMS with these Smad proteins. Consistent with the binding results, overexpression of RBPMS enhances Smad-dependent transcriptional activity in a TGF-beta-dependent manner, whereas knockdown of RBPMS decreases this activity. RBPMS interacts with TGF-beta receptor type I (TbetaR-I), increases phosphorylation of C-terminal SSXS regions in Smad2 and Smad3, and promotes the nuclear accumulation of the Smad proteins. Moreover, RBPMS fails to enhance the transcriptional activity of Smad2 and Smad3 that lack the C-terminal phosphorylation sites. Our data provide the first evidence for an RNA-binding protein playing a role in regulation of Smad-mediated transcriptional activity and suggest that RBPMS stimulates Smad-mediated transactivation possibly through enhanced phosphorylation of Smad2 and Smad3 at the C-terminus and promotion of the nuclear accumulation of the Smad proteins.
Smad2、Smad3和Smad4蛋白被认为是转化生长因子-β（TGF-β）信号传导的关键介质。然而，介导TGF-β信号传导的Smad伴侣的身份尚未完全明确。在此，我们表明，具有多个剪接的RNA结合蛋白（RBPMS），即RNA结合蛋白家族的一员，在体外和体内均与Smad2、Smad3和Smad4发生物理相互作用。TGF-β的存在增加了RBPMS与这些Smad蛋白的结合。与结合结果一致，RBPMS的过表达以TGF-β依赖的方式增强了Smad依赖的转录活性，而RBPMS的敲低则降低了这种活性。RBPMS与I型TGF-β受体（TbetaR-I）相互作用，增加Smad2和Smad3中C末端SSXS区域的磷酸化，并促进Smad蛋白的核积累。此外，RBPMS未能增强缺乏C末端磷酸化位点的Smad2和Smad3的转录活性。我们的数据首次证明了一种RNA结合蛋白在调节Smad介导的转录活性中发挥作用，并表明RBPMS可能通过增强Smad2和Smad3在C末端的磷酸化以及促进Smad蛋白的核积累来刺激Smad介导的反式激活。
