Abstract
The chemokine CXCL10/IP-10 facilitates recruitment of Th1-type leukocytes to inflammatory sites. In this study, we show that the arginine methyltransferase PRMT5 is critical for CXCL10 transcription in TNF-α-activated human endothelial cells (EC). We found that depletion of PRMT5 results in significantly reduced levels of CXCL10 mRNA, demonstrating a positive role for PRMT5 in CXCL10 induction. Chromatin immunoprecipitation experiments revealed the presence of the symmetrical dimethylarginine modification catalyzed by PRMT5 associated with the CXCL10 promoter in response to TNF-α. However, symmetrical dimethylarginine-modified proteins were not detected at the promoter in the absence of PRMT5, indicating that PRMT5 is essential for methylation to occur. Furthermore, NF-κB p65, a critical driver of TNF-α-mediated CXCL10 induction, was determined to be methylated at arginine residues. Crucially, RNAi-mediated PRMT5 depletion abrogated p65 methylation and CXCL10 promoter binding. Mass spectrometric analysis in EC identified five dimethylated arginine residues in p65, four of which are uncharacterized in the literature. Expression of Arg-to-Lys point mutants of p65 demonstrated that both Arg-30 and Arg-35 must be dimethylated to achieve full CXCL10 expression. In conclusion, we have identified previously uncharacterized p65 post-translational modifications critical for CXCL10 induction.