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. (2) and some of the same lysine side chains can be either methylated or acetylated. These modifications alter chromatin structure, often by providing entry sites for proteins that determine higher-order chromatin organization, leading to the activation or inactivation of specific genes. In addition, methylation and demethylation of p53 and NFκB are carried out by enzymes previously known to modify only histones. For p53, the reactions occur on K370, K372, and K382 (3). For NFκB, K37 is methylated by SET9 (4), and K218 and K221 are methylated by NSD1 and demethylated by FBXL11 (5).STAT3 is phosphorylated on tyrosine and serine residues in response to many different cytokines and growth factors, leading to the formation of dimers through reciprocal phosphotyrosine-SH2 interactions (6). Activated STAT3 dimers bind to and activate the promoters of target genes. In addition to phosphorylation, STAT3 was reported to be acetylated at K685 following cytokine stimulation, and the K685R mutation blocked its activation (7), but these observations have been disputed (8). Ray et al. (9) reported that K49 and K87 of STAT3 are acetylated by p300 and that the K-R mutations resulted in a STAT3 protein that is able to translocate into nuclei, but unable to bind to p300. Here, we show that, in response to IL-6, STAT3 is methylated on K140 by the H3K4 methyl transferase SET9 and demethylated by the H3K4 demethylase LSD1 (lysine-specific demethylase 1, also named BHC110). Prevention of methylation by mutation of K140 greatly enhances the induction of one group of genes in response to IL-6, but has little effect on a second group, and inhibits the activation of a third group. Several lines of evidence indicate that methylation takes place as STAT3 is bound to promoters in the f...

Several transcription factors, including p53, NF-κB, and STAT3, are modified by the same enzymes that also modify histones, with important functional consequences. We have identified a previously unrecognized dimethylation of K49 of STAT3 that is crucial for the expression of many IL-6-dependent genes, catalyzed by the histone-modifying enzyme enhancer of zeste homolog 2 (EZH2). Loss of EZH2 is protumorigenic in leukemias, but its overexpression is protumorigenic in solid cancers. Connecting EZH2 to a functionally important methylation of STAT3, which is constitutively activated in many tumors, may help reveal the basis of the opposing roles of EZH2 in liquid and solid tumors and also may identify novel therapeutic opportunities.posttranslational modification | histone methyltransferase | gene expression S TAT3 is activated in 70% of all solid and hematological tumors (1, 2), where it stimulates proliferation, survival, angiogenesis, invasion, and tumor-promoting inflammation. Recently, STAT3 also was found to have an important role in maintaining cancer stem cells, both in vitro and in mouse tumor models, indicating that it is integrally involved in tumor initiation, progression, and maintenance (3). IL-6-induced constitutive activation of STAT3 was observed in neoplastic gastric tissue and is positively correlated with tumor progression (4), and the expression of tyrosine-phosphorylated STAT3 is associated with poor prognosis in colorectal cancer, independent of the mutation status of MSI, CIMP, BRAF, or KRAS (5). The STAT3 gene is rarely mutated in cancer but rather is activated by members of the IL-6 family of cytokines, receptor tyrosine kinases, mutated JAKs, or oncogenic cellular tyrosine kinases, such as SRC (6). Because STAT3 is constitutively activated during disease progression and metastasis, it is a promising therapeutic target. Even though transcription factors are difficult drug targets, accumulating evidence for the crucial roles of posttranslational modifications of transcription factors in mediating target gene expression provides an opportunity to develop drugs against the modifying enzymes rather than against the transcription factors themselves.STAT3 is activated primarily by phosphorylation of Y705 (7) and secondarily by phosphorylation of S727 (8). The acetylation of STAT3 at K685 (9, 10) has been shown recently to have little or no effect on IL-6-dependent gene expression (11). Ray et al. (12) reported that IL-6-induced gene expression requires p300-mediated acetylation of K49 and K87 and that monoubiquitination at K97 is a key mediator of BRD4-dependent gene expression (13). Like NF-κB and p53, STAT3 is reversibly methylated on lysine residues by histone-modifying enzymes, with important functional consequences (14). Furthermore, STAT3 is known to be di-or trimethylated on K140 or K180 by the histone methyltransferase SET9 (SET domain containing lysine methyltransferase 9) or EZH2 (enhancer of zeste homolog 2), respectively (15, 16). Here we show that IL-6-dependent, previously unident...

Background: Lysine acetylation is an important regulatory modification of STAT3. Results: Acetylation of Lys-685 is critical for gene expression driven by unphosphorylated STAT3 (U-STAT3) but not by STAT3 phosphorylated on Tyr-705 (Y-P-STAT3). Conclusion: Distinct modifications regulate U-STAT3 and Y-P-STAT3 differentially. Significance: Lys-685 acetylation could be targeted to block U-STAT3-specific functions, such as activation of oncogene expression.

We used a vector based on the Sleeping Beauty transposon to search for constitutive activators of NFκB in cultured cells. Dominant mutations were produced by random insertion of a tetracycline-regulated promoter, which provided robust and exceptionally well-regulated expression of downstream genes. The ability to regulate the mutant phenotype was used to attribute the latter to the insertional event. In one such mutant, the promoter was inserted in the middle of the gene encoding receptor-interacting protein kinase 1 (RIP1). The protein encoded by the hybrid transcript lacks the putative kinase domain of RIP1, but potently stimulates NFκB, AP-1 and Ets-1 activity. Similarly to TNFα treatment, expression of the short RIP1 was toxic to cells that failed to upregulate NFκB. The effects of short RIP1 did not require endogenous RIP1 or cytokine treatment and coincided with reduced responsiveness to TNFα. Additional evidence indicates that a similar short RIP1 could be produced naturally from the ripk1 locus. Interestingly, elevated expression of short RIP1 resulted in the loss of full length RIP1 from cells, pointing to a novel mechanism through which the abundance of RIP1 and the status of the related signaling cascades may be regulated.