STAT3 regulates Nemo-like kinase by mediating its interaction with IL-6-stimulated TGFβ-activated kinase 1 for STAT3 Ser-727 phosphorylation

Abstract

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-␤-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 TGF␤-induced NLK activation. TGF␤ 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.gp130 ͉ YXXQ motif ͉ signaling specificity T he signal transducer and activator of transcription (STAT) family plays pivotal roles in a variety of systems and in development, in response to cytokines and growth factors. STAT family members are activated in the cytoplasm by tyrosine phosphorylation, form dimers, and enter the nucleus, where they act as DNA-binding transcription factors (1). Of the seven known STATs, STAT1, 3, 5A, 5B, and 6 are phosphorylated at one or two serine residues in their carboxyl-terminal transactivation domain (1, 2) and at a critical tyrosine. The serine phosphorylation enhances the transcriptional activity in the case of STAT1 (3), STAT3 (3, 4), and STAT6 (5). STAT3 can be activated by a variety of cytokines, including the IL-6 family, by using gp130 as a common receptor subunit (6), Granulocyte colony-stimulating factor (G-CSF) and erythropoietin, and growth factors, EGF, platelet-derived growth factor, and hepatocyte growth factor, and cytoplasmic tyrosine kinases, including Src and v-Eyk (reviewed in ref. 7). IL-6 uses STAT3 in its major signaling pathway and concomitantly activates the Ras͞Raf͞ ERK and PI3-kinase pathways (7). IL-6, therefore, activates multiple genes, including acute-phase reactants, and the junB, tis11, stat3, c-myc, and c-fos genes, mostly through STAT3 (8-14). In the IL-6 receptor system, the tyrosine-phosphorylated YXXQ motif of gp130 is critical for recruiting STAT3 for subsequent phosphorylation at Tyr-705 by the associated Jak kinases (15). I...

Signal transducer and activator of transcription 3-regulated sarcoendoplasmic reticulum Ca2+-ATPase 2 expression by prolactin and glucocorticoids is involved in the adaptation of insulin secretory response during the peripartum period

“…Recent evidence suggests that STAT3 serine phosphorylation, which occurs within a mitogen activated protein kinase (MAPK) consensus site (Ser727), has a positive role in STAT3 transcriptional activation (Shen et al 2004, Kojima et al 2005, Sun et al 2006. Indeed, extracellular signal-regulated protein kinases (ERKs) activation targets STAT3 serine phosphorylation (Kuroki & O'Flaherty 1999, O'Rourke & Shepherd 2002.…”

TAB2 Scaffolds TAK1 and NLK in Repressing Canonical Wnt Signaling

“…On the other hand, a recent study showed that TAB2 could also bridge TAK1 with its substrate, such as RCAN1 (36). In the TAK1-NLK cascade, TAK1 activates NLK, but these two proteins do not directly interact with each other (4,5). The finding that TAB2 can scaffold TAK1 and NLK fills the gap and declares the role of TAB2 in directing TAK1 signaling to its specific downstream effector.…”

“…TAK1 is regulated by several distinct extracellular stimuli as previously reported (8,(22)(23)(24). However, only some of them can stimulate the TAK1-NLK cascade (5). This notion suggests that some specific regulation might be required for the signal transduction from TAK1 to NLK.…”

“…Specific interaction or particular scaffold proteins are likely to be required to ensure the fidelity and efficiency of signal flow through kinase cascades (25)(26)(27). However, TAK1 as the activator cannot directly interact with its effector, NLK (4,5). Thus, it is a great possibility that a scaffold protein is involved in the signal transduction from TAK1 to NLK.…”

“…The TAK1-NLK cascade is a mitogen-activated protein kinase (MAPK) 2 -related pathway that regulates a number of biological processes (1)(2)(3)(4)(5)(6)(7). TAK1 (transforming growth factor-␤-activated kinase 1) is a MAPK kinase kinase that was identified by complementation assays to substitute for the MAPKKK ste11 in yeast (8).…”