Miranda Maria Zena, Bialik Janne Folke, Speight Pam, Dan Qinghong, Yeung Tony, Szászi Katalin, Pedersen Stine F, Kapus András
From the Keenan Research Centre for Biomedical Science of the St. Michael's Hospital.
Biochemistry, University of Toronto, Toronto, Ontario M5B 1T8N, Canada and.
J Biol Chem. 2017 Sep 8;292(36):14902-14920. doi: 10.1074/jbc.M117.780502. Epub 2017 Jul 24.
Hippo pathway transcriptional coactivators TAZ and YAP and the TGF-β1 (TGFβ) effector Smad3 regulate a common set of genes, can physically interact, and exhibit multilevel cross-talk regulating cell fate-determining and fibrogenic pathways. However, a key aspect of this cross-talk, TGFβ-mediated regulation of TAZ or YAP expression, remains uncharacterized. Here, we show that TGFβ induces robust TAZ but not YAP protein expression in both mesenchymal and epithelial cells. TAZ levels, and to a lesser extent YAP levels, also increased during experimental kidney fibrosis. Pharmacological or genetic inhibition of Smad3 did not prevent the TGFβ-induced TAZ up-regulation, indicating that this canonical pathway is dispensable. In contrast, inhibition of p38 MAPK, its downstream effector MK2 ( by the clinically approved antifibrotic pirferidone), or Akt suppressed the TGFβ-induced TAZ expression. Moreover, TGFβ elevated TAZ mRNA in a p38-dependent manner. Myocardin-related transcription factor (MRTF) was a central mediator of this effect, as MRTF silencing/inhibition abolished the TGFβ-induced TAZ expression. MRTF overexpression drove the TAZ promoter in a CC(A/T-rich)GG (CArG) box-dependent manner and induced TAZ protein expression. TGFβ did not act by promoting nuclear MRTF translocation; instead, it triggered p38- and MK2-mediated, Nox4-promoted MRTF phosphorylation and activation. Functionally, higher TAZ levels increased TAZ/TEAD-dependent transcription and primed cells for enhanced TAZ activity upon a second stimulus ( sphingosine 1-phosphate) that induced nuclear TAZ translocation. In conclusion, our results uncover an important aspect of the cross-talk between TGFβ and Hippo signaling, showing that TGFβ induces TAZ via a Smad3-independent, p38- and MRTF-mediated and yet MRTF translocation-independent mechanism.
河马通路转录共激活因子TAZ和YAP以及转化生长因子β1(TGFβ)效应分子Smad3调控一组共同的基因,能够发生物理相互作用,并表现出多层次的相互作用,调控细胞命运决定和纤维化途径。然而,这种相互作用的一个关键方面,即TGFβ介导的TAZ或YAP表达调控,仍未得到充分研究。在此,我们表明TGFβ在间充质细胞和上皮细胞中均能诱导强大的TAZ蛋白表达,但不诱导YAP蛋白表达。在实验性肾纤维化过程中,TAZ水平以及程度较轻的YAP水平也会升高。对Smad3进行药理学或遗传学抑制并不能阻止TGFβ诱导的TAZ上调,表明该经典途径并非必需。相反,抑制p38丝裂原活化蛋白激酶(MAPK)、其下游效应分子MK2(通过临床批准的抗纤维化药物吡非尼酮)或Akt可抑制TGFβ诱导的TAZ表达。此外,TGFβ以p38依赖的方式提高TAZ mRNA水平。心肌素相关转录因子(MRTF)是这一效应的核心介质,因为MRTF沉默/抑制可消除TGFβ诱导的TAZ表达。MRTF过表达以CC(A/T丰富)GG(CArG)盒依赖的方式驱动TAZ启动子,并诱导TAZ蛋白表达。TGFβ并非通过促进核MRTF易位发挥作用;相反,它触发p38和MK2介导的、Nox4促进的MRTF磷酸化和激活。在功能上,较高的TAZ水平增加了TAZ/TEAD依赖的转录,并使细胞在第二次刺激(鞘氨醇1-磷酸)诱导核TAZ易位时对增强的TAZ活性产生预适应。总之,我们的结果揭示了TGFβ与河马信号通路之间相互作用的一个重要方面,表明TGFβ通过一种不依赖Smad3、依赖p38和MRTF介导且不依赖MRTF易位的机制诱导TAZ表达。
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