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In cancer cells, endogenous or therapy-induced DNA damage leads to the abnormal presence of DNA in the cytoplasm, which triggers the activation of cGAS (cyclic GMP–AMP synthase) and STING (stimulator of interferon genes). STAT2 suppresses the cGAMP-induced expression of IRF3-dependent genes by binding to STING, blocking its intracellular trafficking, which is essential for the full response to STING activation. STAT2 reshapes STING signaling by inhibiting the induction of IRF3-dependent, but not NF-κB–dependent genes. This noncanonical activity of STAT2 is regulated independently of its tyrosine phosphorylation but does depend on the phosphorylation of threonine 404, which promotes the formation of a STAT2:STING complex that keeps STING bound to the endoplasmic reticulum (ER) and increases resistance to DNA damage. We conclude that STAT2 is a key negative intracellular regulator of STING, a function that is quite distinct from its function as a transcription factor. [ABSTRACT FROM AUTHOR]

Toxic environmental carcinogens promote cancer via genotoxic and nongenotoxic pathways, but nongenetic mechanisms remain poorly characterized. Carcinogen-induced apoptosis may trigger escape from dormancy of microtumors by interfering with inflammation resolution and triggering an endoplasmic reticulum (ER) stress response. While eicosanoid and cytokine storms are wellcharacterized in infection and inflammation, they are poorly characterized in cancer. Here, we demonstrate that carcinogens, such as aflatoxin B1 (AFB1), induce apoptotic cell death and the resulting cell debris stimulates hepatocellular carcinoma (HCC) tumor growth via an "eicosanoid and cytokine storm." AFB1-generated debris up-regulates cyclooxygenase-2 (COX-2), soluble epoxide hydrolase (sEH), ER stressresponse genes including BiP, CHOP, and PDI in macrophages. Thus, selective cytokine or eicosanoid blockade is unlikely to prevent carcinogen-induced cancer progression. Pharmacological abrogation of both the COX-2 and sEH pathways by PTUPB prevented the debris-stimulated eicosanoid and cytokine storm, down-regulated ER stress genes, and promoted macrophage phagocytosis of debris, resulting in suppression of HCC tumor growth. Thus, inflammation resolution via dual COX-2/sEH inhibition is an approach to prevent carcinogen-induced cancer. [ABSTRACT FROM AUTHOR]

Tamoxifen, a widely used modulator of the estrogen receptor (ER), targets ER-positive breast cancer preferentially. We used a powerful validation-based insertion mutagenesis method to find that expression of a dominant-negative, truncated form of the histone deacetylase ZIP led to resistance to tamoxifen. Consistently, increased expression of full-length ZIP gives the opposite phenotype, inhibiting the expression of genes whose products mediate resistance. An important example is JAK2. By binding to two specific sequences in the promoter, ZIP suppresses JAK2 expression. Increased expression and activation of JAK2 when ZIP is inhibited lead to increased STAT3 phosphorylation and increased resistance to tamoxifen, both in cell culture experiments and in a mouse xenograft model. Furthermore, data from human tumors are consistent with the conclusion that decreased expression of ZIP leads to resistance to tamoxifen in ERpositive breast cancer. [ABSTRACT FROM AUTHOR]

Intestinal barrier dysfunction, which leads to translocation of bacteria or toxic bacterial products from the gut into bloodstream and results in systemic inflammation, is a key pathogenic factor in many human diseases. However, the molecular mechanisms leading to intestinal barrier defects are not well understood, and there are currently no available therapeutic approaches to target intestinal barrier function. Here we show that soluble epoxide hydrolase (sEH) is an endogenous regulator of obesity-induced intestinal barrier dysfunction. We find that sEH is overexpressed in the colons of obese mice. In addition, pharmacologic inhibition or genetic ablation of sEH abolishes obesity-induced gut leakage, translocation of endotoxin lipopolysaccharide or bacteria, and bacterial invasion-induced adipose inflammation. Furthermore, systematic treatment with sEH-produced lipid metabolites, dihydroxyeicosatrienoic acids, induces bacterial translocation and colonic inflammation in mice. The actions of sEH are mediated by gut bacteria-dependent mechanisms, since inhibition or genetic ablation of sEH fails to attenuate obesity-induced gut leakage and adipose inflammation in mice lacking gut bacteria. Overall, these results support that sEH is a potential therapeutic target for obesity-induced intestinal barrier dysfunction, and that sEH inhibitors, which have been evaluated in human clinical trials targeting other human disorders, could be promising agents for prevention and/or treatment. [ABSTRACT FROM AUTHOR]

FTO demethylates internal N6-methyladenosine (m6A) and N6,2'-Odimethyladenosine (m6Am; at the cap +1 position) in mRNA, m6A and m6Am in snRNA, and N1-methyladenosine (m1A) in tRNA in vivo, and in vitro evidence supports that it can also demethylate N6-methyldeoxyadenosine (6 mA), 3-methylthymine (3mT), and 3-methyluracil (m3U). However, it remains unclear how FTO variously recognizes and catalyzes these diverse substrates. Here we demonstrate--in vitro and in vivo--that FTO has extensive demethylation enzymatic activity on both internal m6A and cap m6Am. Considering that 6mA, m6A, and m6Am all share the same nucleobase, we present a crystal structure of human FTO bound to 6mAmodified ssDNA, revealing the molecular basis of the catalytic demethylation of FTO toward multiple RNA substrates. We discovered that (i) N6-methyladenine is the most favorable nucleobase substrate of FTO, (ii) FTO displays the same demethylation activity toward internal m6A andm6Am in the same RNA sequence, suggesting that the substrate specificity of FTO primarily results from the interaction of residues in the catalytic pocket with the nucleobase (rather than the ribose ring), and (iii) the sequence and the tertiary structure of RNA can affect the catalytic activity of FTO. Our findings provide a structural basis for understanding the catalytic mechanism through which FTO demethylates its multiple substrates and pave the way forward for the structure-guided design of selective chemicals for functional studies and potential therapeutic applications. [ABSTRACT FROM AUTHOR]

Obesity is associated with enhanced colonic inflammation, which is a major risk factor for colorectal cancer. Considering the obesity epidemic in Western countries, it is important to identify novel therapeutic targets for obesity-induced colonic inflammation, to develop targeted strategies for prevention. Eicosanoids are endogenous lipid signaling molecules involved in regulating inflammation and immune responses. Using an LC-MS/MS-based lipidomics approach, we find that obesity-induced colonic inflammation is associated with increased expression of soluble epoxide hydrolase (sEH) and its eicosanoid metabolites, termed fatty acid diols, in colon tissue. Furthermore, we find that pharmacological inhibition or genetic ablation of sEH reduces colonic concentrations of fatty acid diols, attenuates obesity-induced colonic inflammation, and decreases obesity-induced activation ofWnt signaling in mice. Together, these results support that sEH could be a novel therapeutic target for obesity-induced colonic inflammation and associated diseases. [ABSTRACT FROM AUTHOR]

In response to IFNβ, the IL6 gene is activated, modestly at early times by ISGF3 (IRF9 plus tyrosine-phosphorylated STATs 1 and 2), and strongly at late times by U-ISGF3 (IRF9 plus U-STATs 1 and 2, lacking tyrosine phosphorylation). A classical IFN-stimulated response element (ISRE) at -1,513 to -1,526 in the human IL6 promoter is required. Pretreating cells with IFNβ or increasing the expression of U-STAT2 and IRF9 exogenously greatly enhances IL6 expression in response to the classical NF-κB activators IL1, TNF, and LPS. U-STAT2 binds tightly to IRF9, the DNA binding subunit of ISGF3, and also to the p65 subunit of NF-κB. Therefore, as shown by ChIP analyses, U-STAT2 can bridge the ISRE and κB elements in the IL6 promoter. In some cancer cells, the protumorigenic activation of STAT3 will be enhanced by the increased synthesis of IL6 that is facilitated by high expression of U-STAT2 and IRF9. [ABSTRACT FROM AUTHOR]

The activation of STAT3 by tyrosine phosphorylation, essential for normal development and for a normal inflammatory response to invading pathogens, is kept in check by negative regulators. Abnormal constitutive activation of STAT3, which contributes to the pathology of cancer and to chronic inflammatory diseases such as rheumatoid arthritis, occurs when negative regulation is not fully effective. SOCS3, the major negative regulator of STAT3, is induced by tyrosine-phosphorylated STAT3 and terminates STAT3 phosphorylation about 2 h after initial exposure of cells to members of the IL-6 family of cytokines by binding cooperatively to the common receptor subunit gp130 and JAKs 1 and 2. We show here that when the epidermal growth factor receptor (EGFR) is present and active, STAT3 is rephosphorylated about 4 h after exposure of cells to IL-6 or oncostatin M and remains active for many hours. Newly synthesized IL-6 drives association of the IL-6 receptor and gp130 with EGFR, leading to EGFR-dependent rephosphorylation of STAT3, which is not inhibited by the continued presence of SOCS3. This second wave of STAT3 activation supports sustained expression of a subset of IL-6-induced proteins, several of which play important roles in inflammation and cancer, in which both IL-6 secretion and EGFR levels are often elevated. [ABSTRACT FROM AUTHOR]

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., CD 14) STAT3 target genes. Biological relevance is shown by the observation that overexpression of SOCS3 when k140 cannot be methylatod blocks the ability of cells to activate STAT3 in response to IL-6. 1(140 methylation does not occur with mutants of STAT3 that do not enter nuclei or bind to DNA. Following treatment with lL-6, events at the SOCS3 promoter occur in an ordered sequence, as shown by chromatin immunoprecipitations. Y705-phosphoryl- STAT3 binds first and 5727 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. [ABSTRACT FROM AUTHOR]