Topper J N, DiChiara M R, Brown J D, Williams A J, Falb D, Collins T, Gimbrone M A
Vascular Research Division, Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Proc Natl Acad Sci U S A. 1998 Aug 4;95(16):9506-11. doi: 10.1073/pnas.95.16.9506.
The transforming growth factor-beta (TGF-beta) superfamily of growth factors and cytokines has been implicated in a variety of physiological and developmental processes within the cardiovascular system. Smad proteins are a recently described family of intracellular signaling proteins that transduce signals in response to TGF-beta superfamily ligands. We demonstrate by both a mammalian two-hybrid and a biochemical approach that human Smad2 and Smad4, two essential Smad proteins involved in mediating TGF-beta transcriptional responses in endothelial and other cell types, can functionally interact with the transcriptional coactivator CREB binding protein (CBP). This interaction is specific in that it requires ligand (TGF-beta) activation and is mediated by the transcriptional activation domains of the Smad proteins. A closely related, but distinct endothelial-expressed Smad protein, Smad7, which does not activate transcription in endothelial cells, does not interact with CBP. Furthermore, Smad2,4-CBP interactions involve the COOH terminus of CBP, a region that interacts with other regulated transcription factors such as certain signal transduction and transcription proteins and nuclear receptors. Smad-CBP interactions are required for Smad-dependent TGF-beta-induced transcriptional responses in endothelial cells, as evidenced by inhibition with overexpressed 12S E1A protein and reversal of this inhibition with exogenous CBP. This report demonstrates a functional interaction between Smad proteins and an essential component of the mammalian transcriptional apparatus (CBP) and extends our insight into how Smad proteins may regulate transcriptional responses in many cell types. Thus, functional Smad-coactivator interactions may be an important locus of signal integration in endothelial cells.
转化生长因子-β（TGF-β）超家族的生长因子和细胞因子与心血管系统内的多种生理和发育过程有关。Smad蛋白是最近描述的一类细胞内信号蛋白，可响应TGF-β超家族配体转导信号。我们通过哺乳动物双杂交和生化方法证明，人类Smad2和Smad4这两种在内皮细胞和其他细胞类型中介导TGF-β转录反应所必需的Smad蛋白，能够与转录共激活因子CREB结合蛋白（CBP）发生功能性相互作用。这种相互作用具有特异性，因为它需要配体（TGF-β）激活，并且由Smad蛋白的转录激活域介导。一种密切相关但在内皮细胞中特异性表达的Smad蛋白Smad7，在内皮细胞中不激活转录，也不与CBP相互作用。此外，Smad2、4与CBP的相互作用涉及CBP的COOH末端，该区域与其他受调控的转录因子相互作用，如某些信号转导和转录蛋白以及核受体。Smad与CBP的相互作用是内皮细胞中Smad依赖的TGF-β诱导转录反应所必需的，过表达的12S E1A蛋白抑制作用以及外源性CBP对这种抑制作用的逆转证明了这一点。本报告证明了Smad蛋白与哺乳动物转录装置的一个重要组成部分（CBP）之间的功能性相互作用，并扩展了我们对Smad蛋白如何在许多细胞类型中调节转录反应的认识。因此，功能性Smad-共激活因子相互作用可能是内皮细胞信号整合的一个重要位点。
