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Arginine methyltransferase regulates monocyte extravasation and function

ABSTRACT: Extravasation of monocytes into tissue and to the site of injury is a fundamental immunological process underlying a variety of innate inflammatory responses across multiple organ systems, which requires rapid responses via post translational modifications (PTM) of proteins. Specifically, methylation of protein by arginine methyltransferases (PRMTs) is an epigenetic PTM implicated in inflammatory responses. However, how methyltransferases drive immune regulation particularly in the lung, the resultant tissue injury and whether this might be of therapeutic value has remained unclear. Here, we demonstrate that PRMT7 was increased in the lung of chronic obstructive pulmonary disease (COPD) patients and positively correlated with tissue injury. Accordingly, in clinically relevant models of COPD, lung fibrosis and skin injury, mice with reduced expression of PRMT7 were protected against disease development, due to decreased recruitment of pro-inflammatory monocytes to the site of injury. Mechanistically, we discovered in monocytes activation of NF-κB/RelA induces PRMT7, promoting mono-methylation of histones, which crucially regulates RAP1A and subsequent adhesion and migration ability. Furthermore, in pro-inflammatory monocytes, ALOX5 derived LTB4 induced ACSL4 expression in lung epithelial cells and consequently sensitized towards ferroptosis, thus aggravating tissue injury. Conclusively, specific targeting of arginine mono-methylation offers yet-unappreciated therapeutic potential against monocyte-driven inflammatory conditions.

ORGANISM(S): Mus musculus

PROVIDER: GSE185006 | GEO | 2021/12/16

REPOSITORIES: GEO

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Project description:Protein arginine methylation, catalyzed by the protein arginine methyltransferase (PRMT) family, is recognized as a widespread post-translational modification (PTM) with implications in a plethora of biological processes in eukaryotes. PRMT proteins were classified into three types, type I, II and III, according to the final methyl-arginine products generated. Despite that thousands of substrates have been identified for Type I and II PRMTs, a full scope of arginine methylation catalyzed by the only type III PRMT, PRMT7, as well as its connection with that of type I and II PRMTs remain unknown, limiting our understanding of the network of arginine methylation and its functions in cells. In this study, global profiling of PRMT4 (type I), PRMT5 (type II) and PRMT7 (type III) substrates (also referred as methylome) revealed that PRMT7 methylated a GAR (glycine and arginine) motif similar as PRMT5, while PRMT4 uniquely methylated a motif in which proline was highly enriched. PRMT4, 5 and 7-methylome were all enriched with proteins functioning in mRNA splicing, and knockdown of PRMT4, 5 or 7 led to a global change of alternative splicing events, among which a cohort with implications in cancer development was co-regulated by all three PRMTs. PRMT4, 5 and 7-mediated arginine methylation on splicing factors such as hnRNPA1, though at different status, were shown to enhance RNA binding in general and participate in the regulation of PRMT4, 5 and 7 co-regulated alternative splicing events.The clinical significance of PRMT4, 5 and 7-mediated arginine methylation was underscored by the fact that these three PRMTs as well as hnRNPA1 arginine methylation were over-represented in multiple types of cancers, which were associated with aberrant gene alternative splicing. Consistently, silencing or pharmacological inhibition of PRMT4, 5 and 7 altered gene alternative splicing and suppressed cancer cell growth, and co-treatment exhibited synergistic effects. Taken together, our study provided an integrative view of substrates for the three types of PRMTs, revealing the important function of arginine methylation in RNA splicing and cancer.

Project description:The lymphatic vasculature regulates lung homeostasis through drainage of fluid and trafficking of immune cells and plays a key role in the response to lung injury in several disease states. We have previously shown that lymphatic dysfunction occurs early in the pathogenesis of chronic obstructive pulmonary disease (COPD) caused by cigarette smoke (CS) and that this is associated with increased thrombin and fibrin clots in lung lymph. However, the direct effects of CS and thrombin on lymphatic endothelial cells (LECs) in COPD are not entirely clear. Studies of the blood vasculature have shown that COPD is associated with increased thrombin, which causes endothelial dysfunction after CS exposure and is characterized by changes in the expression of coagulation factors and leukocyte adhesion proteins. Here, we determined whether similar changes occur in LECs. We used an in vitro cell culture system and treated human lung microvascular lymphatic endothelial cells with cigarette smoke extract (CSE) and/or thrombin. We found that CSE treatment led to decreased fibrinolytic activity in LECs, which was associated with increased expression of plasminogen activator inhibitor 1 (PAI-1). LECs treated with both CSE and thrombin together had a decreased expression of TFPI and an increased expression of vascular adhesion molecules. RNA sequencing of lung LECs isolated from mice exposed to CS also showed upregulation of prothrombotic and inflammatory pathways at both acute and chronic exposure time points. Analysis of publicly available single-cell RNA sequencing of LECs as well as immunohistochemical staining of lung tissue from COPD patients supported these data and showed an increased expression of inflammatory markers in LECs from COPD patients compared to those from controls. These studies suggest that in parallel with blood vessels, the lymphatic endothelium undergoes inflammatory changes associated with CS exposure and increased thrombin in COPD. Further research is needed to unravel the mechanisms by which these changes affect lymphatic function and drive tissue injury in COPD.

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Arginine methyltransferase regulates monocyte extravasation and function

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