Repression of Stat3 activity by activation of mitogen-activated protein kinase (MAPK)

Abstract

STAT proteins are activated by phosphorylation at speci®c tyrosine residue at the carboxy-terminus which is required for dimer-formation, nuclear translocation, DNA binding and transcriptional activity in cells treated with cytokines and growth factors. Recent studies have indicated that STATs are also phosphorylated by MAPK, or extracellular signal-regulated kinase (ERK) on serine. We investigated the role of ERK on the regulation of STAT activity. Here, we report that ERK2 activated by its upstream kinase, MEK1, represses Stat3 transcriptional activity induced by Src or Jak-2. To unravel the mechanism of repression, we further showed that Stat3 DNA binding activity and its tyrosine phosphorylation are also inhibited under the same conditions. ERK2 phosphorylates Stat3 on three serinecontaining peptides and decreases its tyrosine phosphorylation induced by EGF treatment. We also detected an association of ERK2 and Stat3 in vivo which is modulated positively by activation of ERK2, but negatively by Jak2. We propose that MAP kinase cascade may negatively regulate Stat3 activities by decreasing its tyrosine phosphorylation and also possibly by association.

Inhibition of IL-6 and IL-10 Signaling and Stat Activation by Inflammatory and Stress Pathways

“…IL-1 inhibited IL-6-mediated Jak-Stat signaling by a rapidly inducible mechanism, and inhibition of IL-6-induced Stat3 activation was mediated by p38, a kinase that is activated by multiple inflammatory/stress factors and has been strongly implicated in driving inflammation (29,30). Previously described inducible mechanisms of inhibition of Jak-Stat signaling involve synthesis of inhibitory proteins such as SOCS (18 -20, 54), potentially target the Stat molecule itself on a conserved carboxyl-terminal serine (serine 727 in Stat3) (58,60,66), or use the ERK subfamily of MAPKs (37) or PKC␣ or PKC␦ isoforms (67). Instead, the mechanism described herein is rapid, independent of de novo expression of inhibitory molecules such as SOCS, independent of modification of Stat3 on serine 727, and occurs at least in part upstream of Stat3 in the IL-6 signaling pathway.…”

“…There is general agreement that phosphorylation of Stat1 and Stat3 on serine 727 enhances the transcriptional potency of tyrosinephosphorylated Stat dimers (46,61,74,76,78,79), and one study suggests that DNA binding is enhanced as well (72). However, several studies have suggested that serine phosphorylation of Stats actually suppresses tyrosine phosphorylation and DNA binding (58,60,66,80), although only one of these studies tested this directly using a mutated Stat (58). We have not excluded that serine phosphorylation of Stats may contribute to modulating Stat activity in our system, but several lines of evidence suggest that the predominant site of inhibition occurs upstream of Stats.…”

The LIM/Homeodomain Protein Islet1 Recruits Janus Tyrosine Kinases and Signal Transducer and Activator of Transcription 3 and Stimulates Their Activities

“…We first examined whether Isl1 affected the endogenous Stat3 transcription activity in various cell lines that were transfected with a reporter gene containing three copies of hSIE followed by the CAT gene (Jain et al, 1998). In COS-1 cells, CAT activity was increased 3.5-fold by Isl1 in unstimulated conditions, which was higher than that stimulated by EGF (3-fold).…”

“…The chloramphenicol acetyltransferase (CAT) assay was performed as described previously (Jain et al, 1998). The firefly luciferase reporter gene constructs m67-hSIE-luc and pGL3 ␣2-M 215luc were gifts from J. Bromberg (Memorial Sloan Kettering Cancer Center, New York, NY) and P. C. Heinrich (RWTH Aachen, Universitats Klinikum, Aachen, Germany), respectively.…”

Kinases: positive and negative regulators of apoptosis

“…30 The regulation of this pathway by the MAP kinases appears to be extremely complex as phosphorylation of the Stats appear to be mediated by multiple components of this pathway and serine phosphorylation of the Stats have been reported to both stimulate and inhibit the transcriptional activity of these proteins. [182][183][184][185] To add another level of complexity into this pathway the Jaks have also been reported to activate the Erk kinases. 186 Stancato et al 187 report that IFN-␥ and oncostatin M both activate Raf-1.…”