Macrophages are a central component of the innate immune response by the production of inflammatory mediators, such as cytokines and chemokines, and by phagocytosis. The production of inflammatory cytokines by macrophages has been linked to inflammatory, autoimmune, and even metabolic diseases. We find that the protein arginine methyltransferase (PRMT) family member Carm1 is a negative regulator of TLR4 induced TNF biosynthesis in macrophages. PRMTs catalyze the addition of a methyl group from S- adenosylmethionine to guanidino nitrogen atoms on arginine residues. Carm1 has classically been described as a transcriptional coactivator. We find that LPS-induced TNF protein levels are increased in Carm1 deficient macrophages, whereas TNF mRNA levels are equivalent, suggesting that Carm1 regulates TNF production post-transcriptionally. In addition, mice bearing a deletion of Carm1 within the macrophage and neutrophil lineages show enhanced susceptibility to the LPS-induced septic shock model, which correlates with increased serum levels of TNF. Negative regulation of TNF by Carm1 through posttranscriptional mechanisms represents a novel mechanism for arginine methyltransferases in regulating innate immunity. The goals of our studies are to identify the mechanism behind Carm1's regulation of TNF biosynthesis. We hypothesize that Carm1 negatively regulates the post-transcriptional processing of TNF. Our proposal has two specific aims.
SPECIFIC AIM 1. To define the intersection of Carm1 with TNF production. We will examine the impact of Carm1 on TNF mRNA splicing, nuclear export of TNF mRNA, TNF message stability, TNF mRNA translation, and TNF protein processing. In this Aim, we will pinpoint the stage(s) of TNF posttranscriptional regulation that intersects with Carm1. The results from this Aim will allow us to focus in on Carm1 substrates from Aim 2 that most likely regulate TNF production. Our TSRI colleague and RNA regulation expert Jamie Williamson will provide guidance for this Aim (see attached letter).
SPECIFIC AIM 2. To build the CARM1-mediated proteomic landscape in macrophages. To better understand the inhibitory role for Carm1 in regulating TNF expression on a molecular level, we will profile the arginine methylation proteome of Carm1 WT and Carm1 KO macrophages using mass spectrometry.
This Aim will be performed in collaboration with the TSRI Center for Physiological Proteomics and Dr. Ben Cravatt's laboratory (see attached letter).
This Aim will be essential to identify the mechanism by which Carm1 regulates TNF processing, follow-up studies for Aim 1.
Macrophages are an essential component of the innate immune response, and we have found that the enzyme Carm1 negatively regulates the production of proinflammatory mediators in macrophages. The goal of this research proposal is to understand the function of arginine methyltransferase Carm1 in macrophages so that we might block its activity during sepsis or promote its activity during vaccinations.
