Belaguli Narasimhaswamy S, Zhang Mao, Rigi Mohammed, Aftab Muhammad, Berger David H
Michael E. DeBakey Dept. of Surgery, Michael E. DeBakey VA Medical Center, Baylor College of Medicine, 2002 Holcombe Blvd., Houston, Texas 77030, USA.
Am J Physiol Gastrointest Liver Physiol. 2007 Jun;292(6):G1520-33. doi: 10.1152/ajpgi.00236.2006. Epub 2007 Feb 8.
Members of the transforming growth factor-beta (TGF-beta) family have been shown to play an important role in the regulation of gut epithelial gene expression. We have used the intestinal alkaline phosphatase (IAP) and intestinal fatty acid binding protein (IFABP) promoters to dissect the mechanisms by which TGF-beta1 signaling regulates gut epithelial gene expression. TGF-beta signaling alone was not sufficient for activation of IAP and IFABP promoters. However, TGF-beta signaling cooperated with the gut epithelial transcription factor GATA4 to synergistically activate IAP and IFABP promoters. Coexpression of GATA4 along with the TGF-beta1 signal transducing downstream effectors such as Smad2, 3, and 4 resulted in synergistic activation of both IAP and IFABP promoters. This synergistic activation was reduced by simultaneous expression of dominant-negative Smad4. -40 and -89 GATA binding sites in the IFABP promoter were required for the synergistic activation by Smad2, 3, and 4 and GATA4. GATA4 and Smad2, 3, and 4 physically associated with each other and this interaction was mediated through the MH2 domain of Smad2, 3, and 4 and the second zinc finger and the COOH-terminal basic domain of GATA4. The COOH-terminal activation domain and the Smad-interacting second zinc finger domain of GATA4 were required for the synergistic activation of the IFABP promoter. Naturally occurring oncogenic mutations within the GATA4-interacting MH2 domain of Smad2 reduced the coactivation of IFABP promoter by Smad2 and GATA4. Our results suggest that the TGF-beta signaling regulates gut epithelial gene expression by targeting GATA4.
转化生长因子-β（TGF-β）家族成员已被证明在肠道上皮基因表达的调控中发挥重要作用。我们利用肠碱性磷酸酶（IAP）和肠脂肪酸结合蛋白（IFABP）启动子来剖析TGF-β1信号传导调节肠道上皮基因表达的机制。单独的TGF-β信号不足以激活IAP和IFABP启动子。然而，TGF-β信号与肠道上皮转录因子GATA4协同激活IAP和IFABP启动子。GATA4与TGF-β1信号转导下游效应分子如Smad2、3和4共表达导致IAP和IFABP启动子的协同激活。显性负性Smad4的同时表达降低了这种协同激活。IFABP启动子中的-40和-89 GATA结合位点是Smad2、3、4和GATA4协同激活所必需的。GATA4与Smad2、3和4相互物理结合，这种相互作用通过Smad2、3和4的MH2结构域以及GATA4的第二个锌指和COOH末端碱性结构域介导。GATA4的COOH末端激活结构域和与Smad相互作用的第二个锌指结构域是IFABP启动子协同激活所必需的。Smad2与GATA4相互作用的MH2结构域内的天然致癌突变降低了Smad2和GATA4对IFABP启动子的共激活作用。我们的结果表明，TGF-β信号通过靶向GATA4来调节肠道上皮基因表达。
