Hanafusa H, Ninomiya-Tsuji J, Masuyama N, Nishita M, Fujisawa J, Shibuya H, Matsumoto K, Nishida E
Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
J Biol Chem. 1999 Sep 17;274(38):27161-7. doi: 10.1074/jbc.274.38.27161.
Transforming growth factor-beta (TGF-beta)-activated kinase 1 (TAK1), a member of the mitogen-activated protein kinase kinase kinase family, is suggested to be involved in TGF-beta-induced gene expression, but the signaling mechanism from TAK1 to the nucleus remains largely undefined. We have found that p38 mitogen-activated protein kinase, and its direct activator MKK6 are rapidly activated in response to TGF-beta. Expression of dominant negative MKK6 or dominant negative TAK1 inhibited the TGF-beta-induced transcriptional activation as well as the p38 activation. Constitutive activation of the p38 pathway in the absence of TGF-beta induced the transcriptional activation, which was enhanced synergistically by coexpression of Smad2 and Smad4 and was inhibited by expression of the C-terminal truncated, dominant negative Smad4. Furthermore, we have found that activating transcription factor-2 (ATF-2), which is known as a nuclear target of p38, becomes phosphorylated in the N-terminal activation domain in response to TGF-beta, that ATF-2 forms a complex with Smad4, and that the complex formation is enhanced by TGF-beta. In addition, expression of a nonphosphorylatable form of ATF-2 inhibited the TGF-beta-induced transcriptional activation. These results show that the p38 pathway is activated by TGF-beta and is involved in the TGF-beta-induced transcriptional activation by regulating the Smad-mediated pathway.
转化生长因子-β（TGF-β）激活激酶1（TAK1）是丝裂原活化蛋白激酶激酶激酶家族的成员之一，据推测其参与TGF-β诱导的基因表达，但从TAK1到细胞核的信号传导机制仍不清楚。我们发现，p38丝裂原活化蛋白激酶及其直接激活剂MKK6可对TGF-β作出快速激活反应。显性负性MKK6或显性负性TAK1的表达可抑制TGF-β诱导的转录激活以及p38的激活。在无TGF-β的情况下，p38途径的组成型激活可诱导转录激活，与Smad2和Smad4共表达可协同增强该激活作用，而C末端截短的显性负性Smad4的表达则可抑制该激活作用。此外，我们发现，作为p38核内靶点的激活转录因子-2（ATF-2）可对TGF-β作出反应，在其N末端激活域发生磷酸化，ATF-2与Smad4形成复合物，且TGF-β可增强该复合物的形成。此外，不可磷酸化形式的ATF-2的表达可抑制TGF-β诱导的转录激活。这些结果表明，p38途径可被TGF-β激活，并通过调节Smad介导的途径参与TGF-β诱导的转录激活。
