Xing Chen

Reversible methylation of promoter-bound STAT3 by histone-modifying enzymes

Following its tyrosine phosphorylation, STAT3 is methylated on K140 by the histone methyl transferase SET9 and demethylated by LSD1 when it is bound to a subset of the promoters that it activates. Methylation of K140 is a negative regulatory event, because its blockade greatly increases the steady-state amount of activated STAT3 and the expression of many (i.e., SOCS3) but not all (i.e., CD14) STAT3 target genes. Biological relevance is shown by the observation that overexpression of SOCS3 when K140 cannot be methylated blocks the ability of cells to activate STAT3 in response to IL-6. K140 methylation does not occur with mutants of STAT3 that do not enter nuclei or bind to DNA. Following treatment with IL-6, events at the SOCS3 promoter occur in an ordered sequence, as shown by chromatin immunoprecipitations. Y705-phosphoryl-STAT3 binds first and S727 is then phosphorylated, followed by the coincident binding of SET9 and dimethylation of K140, and lastly by the binding of LSD1. We conclude that the lysine methylation of promoter-bound STAT3 leads to biologically important down-regulation of the dependent responses and that SET9, which is known to help provide an activating methylation mark to H3K4, is recruited to the newly activated SOCS3 promoter by STAT3.

A novel IL-17 signaling pathway controlling keratinocyte proliferation and tumorigenesis via the TRAF4-ERK5 axis.

Wu et al. report a novel IL-17–mediated cascade via the IL-17R–TRAF4–ERK5 axis that directly stimulates keratinocyte proliferation and skin tumor formation in mice.

STAT3 mutations correlated with hyper-IgE syndrome lead to blockage of IL-6/STAT3 signalling pathway

Of all the causes identified for the disease hyper-immunoglobulinemia E syndrome (HIES), a homozygous mutation in tyrosine kinase2 (TYK2) and heterozygous mutations in STAT3 are implicated the defects in Jak/STAT signalling pathway in the pathogenesis of HIES. Mutations of STAT3 have been frequently clinically identified in autosomal-dominant (AD) HIES patients’ cells, and therefore, the genotype of STAT3 has been associated with the phenotype of HIES. Here, we conducted studies on the functional loss of the seven specific STAT3 mutations correlated with AD-HIES. Using STAT3-null human colon carcinoma cell line A4 cells, we generated seven mutants of STAT3 bearing single mutations clinically identified in AD-HIES patients’ cells and studied the functional loss of these mutants in IL-6-Jak/STAT3 signalling pathway. Our results show that five STAT3 mutants bearing mutations in the DNA-binding domain maintain the phosphorylation of Tyr705 and the ability of dimerization while the other two with mutations in SH2 domain are devoid of the phosphorylation of Try705 and abrogate the dimerization in response to IL-6. The phosphorylation of Ser727 in these mutants shows diversity in response to IL-6. These mutations eventually converge on the abnormalities of the IL-6/Gp130/Jak2-mediated STAT3 transactivation on target genes, indicative of the dysregulation of JAK/STAT signalling present in HIES.

TPCA-1 Is a Direct Dual Inhibitor of STAT3 and NF-κB and Regresses Mutant EGFR-Associated Human Non–Small Cell Lung Cancers

Epidermal growth factor receptor (EGFR) is a clinical therapeutic target to treat a subset of non–small cell lung cancer (NSCLC) harboring EGFR mutants. However, some patients with a similar kind of EGFR mutation show intrinsic resistance to tyrosine kinase inhibitors (TKI). It indicates that other key molecules are involved in the survival of these cancer cells. We showed here that 2-[(aminocarbonyl)amino]-5 -(4-fluorophenyl)-3- thiophenecarboxamide (TPCA-1), a previously reported inhibitor of IκB kinases (IKK), blocked STAT3 recruitment to upstream kinases by docking into SH2 domain of STAT3 and attenuated STAT3 activity induced by cytokines and cytoplasmic tyrosine kinases. TPCA-1 is an effective inhibitor of STAT3 phosphorylation, DNA binding, and transactivation in vivo. It selectively repressed proliferation of NSCLC cells with constitutive STAT3 activation. In addition, using pharmacologic and genetic approaches, we found that both NF-κB and STAT3 could regulate the transcripts of interleukin (IL)-6 and COX-2 in NSCLC harboring EGFR mutations. Moreover, gefitinib treatment only did not efficiently suppress NF-κB and STAT3 activity. In contrast, we found that treatment with TKIs increased phosho-STAT3 level in target cells. Inhibiting EGFR, STAT3, and NF-κB by combination of TKIs with TPCA-1 showed increased sensitivity and enhanced apoptosis induced by gefitinib. Collectively, in this work, we identified TPCA-1 as a direct dual inhibitor for both IKKs and STAT3, whereas treatment targeting EGFR only could not sufficiently repress NF-κB and STAT3 pathways for lung cancers harboring mutant EGFR. Therefore, synergistic treatment of TPCA-1 with TKIs has potential to be a more effective strategy for cancers. Mol Cancer Ther; 13(3); 617–29. ©2014 AACR.

Brevilin A, a Novel Natural Product, Inhibits Janus Kinase Activity and Blocks STAT3 Signaling in Cancer Cells

Signal abnormalities in human cells usually cause unexpected consequences for individual health. We focus on these kinds of events involved in JAK-STAT signal pathways, especially the ones triggered by aberrant activated STAT3, an oncoprotein which participates in essential processes of cell survival, growth and proliferation in many types of tumors, as well as immune diseases. By establishing a STAT3 signal based high-throughput drug screening system in human lung cancer A549 cells, we have screened a library from natural products which contained purified compounds from medicinal herbs. One compound, named Brevilin A, exhibited both strong STAT3 signal inhibition and STAT3 signal dependent cell growth inhibition. Further investigations revealed that Brevilin A not only inhibits STAT3 signaling but also STAT1 signaling for cytokines induced phosphorylation of STAT3 and STAT1 as well as the expression of their target genes. In addition, we found Brevilin A could attenuate the JAKs activity by blocking the JAKs tyrosine kinase domain JH1. The levels of cytokine induced phosphorylation of STATs and other substrates were dramatically reduced by treatment of Brevilin A. The roles of Brevilin A targeting on JAKs activity indicate that Brevilin A may not only be used as a STAT3 inhibitor but also a compound blocking other JAK-STAT hyperactivation. Thus, these findings provided a strong impetus for the development of selective JAK-STAT inhibitors and therapeutic drugs in order to improve survival of patients with hyperactivated JAKs and STATs.

Activation of Akt protects cancer cells from growth inhibition induced by PKM2 knockdown

BackgroundPKM2 is an attractive target for cancer therapy, however, for many cancer cells, PKM2 knockdown only leads to a modest impairment of survival and proliferation. It is not known whether PKM2 knockdown rewires cell signaling pathways in these “PKM2 knockdown resistant” cells, and whether the rewired pathways are needed for their survival.FindingsIn present study, we investigated the effects of PKM2 knockdown on cellular signaling pathways in “PKM2 knockdown resistant” cancer cells. We found that knockdown of PKM2 leads to activation of Akt. Furthermore, we revealed that activation of Akt in PKM2 knockdown cells is a result of glycolysis disruption. Inhibiton of PI3K-Akt signaling pathway leads to significant growth inhibition and apoptosis in PKM2 knockdown cells.ConclusionsOverall, our results indicate that activation of Akt is necessary for the survival of PKM2 knockdown cells. Combing PKM2 knockdown with PI3K or Akt inhibitors may lead to a better chance to kill tumors. Our research may provide an unexpected opportunity for the development and implementation of drugs targeting cell metabolism and aberrant Akt signaling.

Correction: Neuron-Specific HuR-Deficient Mice Spontaneously Develop Motor Neuron Disease

Sun, K., X. Li, X. Chen, Y. Bai, G. Zhou, O. N. Kokiko-Cochran, B. Lamb, T. A. Hamilton, C.-Y. Lin, Y.-S. Lee, and T. Herjan. 2018. Neuron-specific HuR-deficient mice spontaneously develop motor neuron disease. J . Immunol . 201: [157–166][1]. The National Multiple Sclerosis Society grant number

Dehydrocrenatidine is a novel janus kinase inhibitor

Janus kinase (JAK) 2 plays a pivotal role in the tumorigenesis of signal transducers and activators of transcription (STAT) 3 constitutively activated solid tumors. JAK2 mutations are involved in the pathogenesis of various types of hematopoietic disorders, such as myeloproliferative disorders, polycythemia vera, essential thrombocythemia, and primary myelofibrosis. Thus, small-molecular inhibitors targeting JAK2 are potent for therapy of these diseases. In this study, we screened 1,062,608 drug-like molecules from the ZINC database and 2080 natural product chemicals. We identified a novel JAK family kinase inhibitor, dehydrocrenatidine, that inhibits JAK-STAT3–dependent DU145 and MDA-MB-468 cell survival and induces cell apoptosis. Dehydrocrenatidine represses constitutively activated JAK2 and STAT3, as well as interleukin-6–, interferon-α−, and interferon-γ–stimulated JAK activity, and STAT phosphorylation, and suppresses STAT3 and STAT1 downstream gene expression. Dehydrocrenatidine inhibits JAKs-JH1 domain overexpression–induced STAT3 and STAT1 phosphorylation. In addition, dehydrocrenatidine inhibits JAK2-JH1 kinase activity in vitro. Importantly, dehydrocrenatidine does not show significant effect on Src overexpression and epidermal growth factor–induced STAT3 activation. Our results indicate that dehydrocrenatidine is a JAK-specific inhibitor.