Response to Matters Arising

to our findings. The authors further state that " … the same observations were also made for STAT6 (Chen et al., 2004). " Meissner et al. incubated the cells with MTA In their Matters Arising article, Meissner et al. present several experiments that call into question our conclu-in DMSO, whereas we had solubilized MTA in tissue culture media. While somewhat unexpected, this differ-sions from the results reported in our original manuscript (Mowen et al., 2001). We clearly acknowledge the impor-ence in solvents used seems to make a significant difference (see Figure 1): when dissolved in DMSO, MTA does tance of these new findings, but at the same time have reservations about the extent to which these results indeed block STAT1 tyrosine phosphorylation. However, when MTA is dissolved in media (as was done in our invalidate our conclusions of STAT1 arginine methyl-ation. original studies to completely block IFN␣/␤-mediated ISG induction), no inhibition of STAT1 tyrosine phos-We had employed monoclonal antibodies against di-methylarginine (DMA) to demonstrate methylation of phorylation is observed. While we cannot offer an explanation for these different, solvent-dependent effects of STAT1 in vivo. Since the antibody was ineffective in Western blots, we performed immunoprecipiations, fol-MTA, the finding nevertheless invalidates the notion that mere inhibition of STAT1 tyrosine phosphorylation ac-lowed by anti-STAT1 immunoblotting. Specificity of the antibodies was demonstrated by the fact that only a counts for the inhibitory effects of MTA on IFN␣/␤-induced gene transcription. In addition, the paper reporting methylated STAT1 N-terminal domain could successfully compete for binding to the DMA antibody. Other STAT6 arginine methylation quoted in this context by the authors clearly shows that STAT6, but not STAT1 labs have in the meantime reproduced these findings for STAT1, STAT3, and STAT6 (Chen et al., 2004; Duong tyrosine phosphorylation is inhibited by the methyltrans-ferase inhibitors (Chen et al. of high-stringent immunoprecipitation condition, coim-MTA-mediated inhibition of STAT1 tyrosine phosphory-lation cannot explain the increased PIAS association munoprecipitation of STAT proteins with associated, ar-ginine-methylated proteins can naturally not be defini-with hypomethylated STAT1 we and others have observed (Duong et al., 2004). The fact that MTA also tively excluded in these experiments. However, Rho et al. reported the arginine methylation of STAT3 (Rho et blocks an NF-␬B luciferase does not justify the conclusion that it is a nonspecific transcriptional inhibitor. The al., 2001). This study not only used the DMA antibody for immunoprecipitation followed by STAT3 Western inhibitory effect of MTA …