Abdollah S, Macías-Silva M, Tsukazaki T, Hayashi H, Attisano L, Wrana J L
Program in Developmental Biology and Division of Gastroenterology, The Hospital for Sick Children, Toronto, Ontario, Canada, M5G 1X8.
J Biol Chem. 1997 Oct 31;272(44):27678-85. doi: 10.1074/jbc.272.44.27678.
Mothers against Dpp-related or Smad proteins are essential components of serine/threonine kinase receptor signaling pathways that are regulated by phosphorylation. Recently, it was demonstrated that Smad2 interacts transiently with and is a direct substrate of the transforming growth factor-beta (TGF-beta) type I receptor, TbetaRI. Phosphorylation sites on Smad2 were localized to a carboxyl-terminal fragment containing three serine residues at positions 464, 465, and 467. In this report, we show that TbetaRI specifically phosphorylates Smad2 on serines 465 and 467. Serine 464 is not a site of phosphorylation, but is important for efficient phosphorylation of Smad2. Phosphorylation at both sites is required to mediate association of Smad2 with Smad4 in mammalian cells, while in yeast, Smad2 interacts directly with Smad4 and does not require phosphorylation. Mutation of either serine residue 465 or 467 prevents dissociation of Smad2 from activated TbetaRI and blocks TGF-beta-dependent signaling and Smad2 transcriptional activity. These results indicate that receptor-dependent phosphorylation of Smad2 on serines 465 and 467 is required in mammalian cells to permit association with Smad4 and to propagate TGF-beta signals.
与Dpp相关的蛋白或Smad蛋白是丝氨酸/苏氨酸激酶受体信号通路的重要组成部分，这些信号通路受磷酸化调节。最近，有研究表明Smad2与转化生长因子-β（TGF-β）I型受体TβRI短暂相互作用，并且是其直接底物。Smad2上的磷酸化位点定位于一个羧基末端片段，该片段在464、465和467位含有三个丝氨酸残基。在本报告中，我们表明TβRI特异性地使Smad2的465位和467位丝氨酸磷酸化。464位丝氨酸不是磷酸化位点，但对Smad2的有效磷酸化很重要。在这两个位点的磷酸化是介导Smad2与Smad4在哺乳动物细胞中缔合所必需的，而在酵母中，Smad2直接与Smad4相互作用，不需要磷酸化。465位或467位丝氨酸残基的突变会阻止Smad2从活化的TβRI上解离，并阻断TGF-β依赖的信号传导和Smad2转录活性。这些结果表明，在哺乳动物细胞中，Smad2在465位和467位丝氨酸上的受体依赖性磷酸化是与Smad4缔合并传递TGF-β信号所必需的。
