Kojima Hirotada, Sasaki Takanori, Ishitani Tohru, Iemura Shun-ichiro, Zhao Hong, Kaneko Shuhei, Kunimoto Hiroyuki, Natsume Tohru, Matsumoto Kunihiro, Nakajima Koichi
Department of Immunology, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi, Abeno-ku, Osaka 545-8585, Japan.
Proc Natl Acad Sci U S A. 2005 Mar 22;102(12):4524-9. doi: 10.1073/pnas.0500679102. Epub 2005 Mar 11.
Signal transducer and activator of transcription 3 (STAT3) is activated by the IL-6 family of cytokines and growth factors. STAT3 requires phosphorylation on Ser-727, in addition to tyrosine phosphorylation on Tyr-705, to be transcriptionally active. In IL-6 signaling, the two major pathways that derive from the YXXQ and the YSTV motifs of gp130 cause Ser-727 phosphorylation. Here, we show that TGF-beta-activated kinase 1 (TAK1) interacts with STAT3, that the TAK1-Nemo-like kinase (NLK) pathway is efficiently activated by IL-6 through the YXXQ motif, and that this is the YXXQ-mediated H7-sensitive pathway that leads to STAT3 Ser-727 phosphorylation. Because NLK was recently shown to interact with STAT3, we explored the role of STAT3 in activating this pathway. Depletion of STAT3 diminished the IL-6-induced NLK activation by >80% without inhibiting IL-6-induced TAK1 activation or its nuclear entry. We found that STAT3 functioned as a scaffold for TAK1 and NLK in vivo through a region in its carboxyl terminus. Furthermore, the expression of the STAT3(534-770) region in the nuclei of STAT3-knockdown cells enhanced the IL-6-induced NLK activation in a dose-dependent manner but not the TGFbeta-induced NLK activation. TGFbeta did not cause STAT3 Ser-727 phosphorylation, even when the carboxyl region of STAT3 was expressed in the nuclei. Together, these results indicate that STAT3 enhances the efficiency of its own Ser-727 phosphorylation by acting as a scaffold for the TAK1-NLK kinases, specifically in the YXXQ motif-derived pathway.
信号转导与转录激活因子3（STAT3）可被白细胞介素-6（IL-6）家族的细胞因子和生长因子激活。STAT3除了在酪氨酸705位点发生磷酸化外，还需要在丝氨酸727位点发生磷酸化才能具有转录活性。在IL-6信号通路中，源自gp130的YXXQ和YSTV基序的两条主要途径可导致丝氨酸727位点磷酸化。在此，我们表明转化生长因子-β激活激酶1（TAK1）与STAT3相互作用，IL-6可通过YXXQ基序有效激活TAK1-Nemo样激酶（NLK）途径，且这是导致STAT3丝氨酸727位点磷酸化的YXXQ介导的H7敏感途径。由于最近发现NLK与STAT3相互作用，我们探究了STAT3在激活该途径中的作用。STAT3的缺失使IL-6诱导的NLK激活减少了80%以上，而不抑制IL-6诱导的TAK1激活或其进入细胞核。我们发现STAT3在体内通过其羧基末端的一个区域作为TAK1和NLK的支架发挥作用。此外，在STAT3敲低细胞的细胞核中表达STAT3（534-770）区域以剂量依赖的方式增强了IL-6诱导的NLK激活，但不增强转化生长因子-β诱导的NLK激活。即使在细胞核中表达STAT3的羧基区域，转化生长因子-β也不会导致STAT3丝氨酸727位点磷酸化。总之，这些结果表明STAT3通过作为TAK1-NLK激酶的支架，特别是在源自YXXQ基序的途径中，提高了其自身丝氨酸727位点磷酸化的效率。
