Constitutive Stat3, Tyr705, Ser727 phosphorylation in acute myeloid leukemia cells caused by the autocrine secretion of interleukin-6

Department of Hematology, University Hospital Groningen, Groningen, The Netherlands.
Blood (Impact Factor: 10.43). 07/2000; 95(12):3765-70.
Source: PubMed

ABSTRACT To explore the activation patterns of signal transducer and activator of transcription 3 (Stat3) in acute myeloid leukemia (AML), we examined whether the phosphorylation of tyrosine705 (Tyr705) and serine727 (Ser727) residues was abnormally regulated in cells from patients with AML. In 5 of 20 (25%) patients with AML, Stat3 was constitutively phosphorylated on Tyr705 and Ser727, which were not further up-regulated by treatment with IL-6. Furthermore, Stat3 was constitutively bound to the IRE response element in these cells as determined by electrophoretic mobility shift assay, and stimulation with IL-6 did not result in increased DNA binding. Interestingly, AML cells with constitutive Stat3 activation also secreted high levels of IL-6 protein. Treating these AML cells with anti-IL-6 resulted in restored IL-6-inducible Stat3 phosphorylation on both Tyr705 and Ser727 with low or undetectable basal phosphorylation levels in unstimulated cells. In contrast, treatment with anti-IL-1 did not result in altered Stat3 phosphorylation patterns. The constitutive IL-6 expression was associated with elevated levels of suppressor of cytokine signaling-1 (SOCS-1) and SOCS-3 mRNA expression, which were not down-regulated by anti-IL-6. These data indicate that the constitutive Stat3 activation in the investigated AML blasts is caused by high IL-6 secretion levels, thus stimulating the Jak/Stat pathway in an autocrine manner, a paracrine manner, or both. (Blood. 2000;95:3765-3770)

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    • "To date, conflicting evidence exists concerning the kinase responsible for STAT3 (ser727) phosphorylation. Some members of the MAPK family, such as Protein kinase C, Jun N-terminal kinase, extracellular signal-regulated kinase1/2 (ERK1/2), p38, and mammalian target of rapamycin (mTOR), seem to be involved, but their implications remain unclear [25] [26] [29] [30]. The apparent divergence of results may be due to the variation of cell systems and stimuli employed in the different studies. "
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    ABSTRACT: Invasiveness of trophoblast and choriocarcinoma cells is in part mediated via leukemia inhibitory factor- (LIF-) induced activation of signal transducer and activator of transcription 3 (STAT3). The regulation of STAT3 phosphorylation at its ser727 binding site, possible crosstalk with intracellular MAPK signaling, and their functional implications are the object of the present investigation. JEG-3 choriocarcinoma cells were cultured in presence/absence of LIF and the specific ERK1/2 inhibitor (U0126). Phosphorylation of signaling molecules (p-STAT3 (ser727 and tyr705) and p-ERK1/2 (thr 202/tyr 204)) was assessed per Western blot. Immunocytochemistry confirmed results, but also pinpointed the location of phosphorylated signaling molecules. STAT3 DNA-binding capacity was studied with a colorimetric ELISA-based assay. Cell viability and invasion capability were assessed by MTS and Matrigel assays. Our results demonstrate that LIF-induced phosphorylation of STAT3 (tyr705 and ser727) is significantly increased after blocking ERK1/2. STAT3 DNA-binding capacity and cell invasiveness are enhanced after LIF stimulation and ERK1/2 blockage. In contrast, proliferation is enhanced by LIF but reduced after ERK1/2 inhibition. The findings herein show that blocking ERK1/2 increases LIF-induced STAT3 phosphorylation and STAT3 DNA-binding capacity by an intranuclear crosstalk, which leads to enhanced invasiveness and reduced proliferation.
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    • "Third, studies show that flavopiridol disrupts STAT3 function by blocking its binding to DNA in tumor cells [15]. Because STAT3 is constitutively active in many subtypes of leukemia and serves as a central regulator in multiple pro-survival and oncogenic signaling pathways [19] [20] [21], flavopiridol could block the tumor promoting pathways induced by STAT3. Given the pleiotropic effects of flavopiridol, it is likely that it functions through additional, unknown molecular pathways. "
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    • "STAT3 is implicated in the transcriptional reciprocation of genes that are associated with cell proliferation and survival. STAT3 is activated by IL-6 cytokine and leptin as well as other growth factors, including epidermal growth factor receptor (EGFR), fibroblast growth factor receptor (FGFR), and plateletderived growth factor receptor (PDGFR) through tyrosine phosphorylation [12]. After dimerization, STAT3 translocates into Journal of Hepatology 2011 vol. "
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