Lue Hongqi, Kapurniotu Aphrodite, Fingerle-Rowson Günter, Roger Thierry, Leng Lin, Thiele Michael, Calandra Thierry, Bucala Richard, Bernhagen Jürgen
Department of Biochemistry and Molecular Cell Biology, Institute of Biochemistry, University Hospital of the RWTH Aachen, Pauwelsstrasse 30, D-52074 Aachen, Germany.
Cell Signal. 2006 May;18(5):688-703. doi: 10.1016/j.cellsig.2005.06.013. Epub 2005 Aug 24.
Macrophage migration inhibitory factor (MIF) is a 12.5 kD polypeptide that serves as a critical regulator of cell functions such as gene expression, proliferation or apoptosis. However, the signal transduction pathways through which MIF takes part in cellular regulation are only incompletely understood. MIF leads to CD74-dependent "sustained" activation of ERK1/2 MAPK, but MIF's role in "transient" ERK activation and the involved upstream pathways are unknown. Here we report that the transient ERK pathway was markedly activated by MIF. This effect involved the phosphorylation and activation of Raf-1, MEK, ERK, and Elk-1. Of note, rapid and transient ERK phosphorylation by MIF was measurable in MIF-deficient cells, suggesting that MIF acted in a non-autocrine fashion. Applying the inhibitor genistein, a tyrosine kinase (TPK) activity was identified as a critical upstream signalling event in MIF-induced transient ERK signalling. Experiments using the Src kinase inhibitor PP2 indicated that the involved TPK was a Src-type tyrosine kinase. A role for an upstream Src kinase was proven by applying Src-deficient cells which did not exhibit transient ERK activation upon treatment with MIF, but in which MIF-induced ERK signalling could be restored by re-expressing Src. Intriguingly, JAB1/CSN5, a signalosome component, cellular binding protein of MIF and regulator of cell proliferation and survival, had a marked, yet dual, effect on MIF-induced ERK signalling. JAB1 overexpression inhibited sustained, but not transient, ERK phosphorylation. By contrast, JAB1-knock-down by siRNA revealed that minimum JAB1 levels were necessary for transient activation of ERK by MIF. In conclusion, MIF rapidly and transiently activates the ERK pathway, an effect that has not been recognized previously. This signalling pathway involves the upstream activation of a Src-type kinase and is co-regulated by the cellular MIF binding protein JAB1/CSN5. Our study thus has unravelled a novel MIF-driven signalling pathway and an intricate regulatory system involving extra- and possibly intracellular MIF, and which likely critically participates in controlling cell proliferation and survival.
巨噬细胞移动抑制因子（MIF）是一种12.5千道尔顿的多肽，它是细胞功能如基因表达、增殖或凋亡的关键调节因子。然而，MIF参与细胞调节的信号转导途径目前仅得到部分了解。MIF可导致依赖CD74的ERK1/2丝裂原活化蛋白激酶（MAPK）的“持续”激活，但MIF在“瞬时”ERK激活及相关上游途径中的作用尚不清楚。在此我们报告，MIF可显著激活瞬时ERK途径。这种效应涉及Raf-1、MEK、ERK和Elk-1的磷酸化及激活。值得注意的是，在MIF缺陷细胞中可检测到MIF诱导的快速且瞬时的ERK磷酸化，这表明MIF以非自分泌方式发挥作用。应用抑制剂染料木黄酮，酪氨酸激酶（TPK）活性被确定为MIF诱导的瞬时ERK信号传导中的关键上游信号事件。使用Src激酶抑制剂PP2的实验表明，所涉及的TPK是一种Src型酪氨酸激酶。通过应用Src缺陷细胞证实了上游Src激酶的作用，在用MIF处理时，这些细胞未表现出瞬时ERK激活，但通过重新表达Src可恢复MIF诱导的ERK信号传导。有趣的是，信号体成分、MIF的细胞结合蛋白以及细胞增殖和存活调节因子JAB1/CSN5对MIF诱导的ERK信号传导具有显著但双重的影响。JAB1过表达抑制持续的ERK磷酸化，但不抑制瞬时的ERK磷酸化。相反，通过小干扰RNA敲低JAB1显示，最低JAB1水平是MIF瞬时激活ERK所必需的。总之，MIF快速且瞬时地激活ERK途径，这一效应此前未被认识到。该信号通路涉及Src型激酶的上游激活，并由细胞MIF结合蛋白JAB1/CSN5共同调节。因此，我们的研究揭示了一种新的MIF驱动的信号通路以及一个复杂的调节系统，该系统涉及细胞外及可能的细胞内MIF，并且可能在控制细胞增殖和存活中起关键作用。
