Oct. 27, 2011
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.
Figure Nuclear import and DNA binding are required for IL-6.induced S727 phosphorylation and K140 dimethylation of STAT3. (C) A4 cells expressing wild-type STAT3 were grown on coverslips to 20 to 30% confluence, then treated with IL-6 for 4 h, followed by staining with primary antibodies directed against STAT3, S727-phosphoryl-STAT3 and STAT3-K140me2. Following staining with DAPI (blue nuclear stain) and fluorescent secondary antibodies against STAT3 (green), S727-phosphoryl-STAT3 (red) or STAT3-K140me2 (red), the cells were examined by confocal microscopy. The yellow/pink pixels in the composite image demonstrate the close association of the two proteins.
Results from: Yang, J. , Huang, J. , Dasgupta, M. , Sears, N. , Miyagi, M. , Wang, B. , Chance, M.R. , Chen, X. , Du, Y., Wang, Y., An, L. ,Wang, Q. ,Lu, T. ,Zhang, X. , Wang, Z., Stark, G.R. Proceedings of the National Academy of the Sciences USA 107(50): 21499-504, 2010. PMCID: PMC3003019