The cyclic GMP-AMP synthase (cGAS), upon cytosolic DNA stimulation, catalyzes the formation of the second messenger 2′3′-cGAMP, which then binds to stimulator of interferon genes (STING) and activates downstream signaling. It remains to be elucidated how the cGAS enzymatic activity is modulated dynamically. Here, we reported that the ER ubiquitin ligase RNF185 interacted with cGAS during HSV-1 infection. Ectopic-expression or knockdown of RNF185 respectively enhanced or impaired the IRF3-responsive gene expression. Mechanistically, RNF185 specifically catalyzed the K27-linked poly-ubiquitination of cGAS, which promoted its enzymatic activity. Additionally, Systemic Lupus Erythematosus (SLE) patients displayed elevated expression of RNF185 mRNA. Collectively, this study uncovers RNF185 as the first E3 ubiquitin ligase of cGAS, shedding light on the regulation of cGAS activity in innate immune responses. Ubiquitination has been demonstrated to serve as an effective means to catalyze the rapid, dynamic and versatile regulatory processes that are activated when hosts face microbes. Given the critical functions of cytosolic DNA sensing pathway in anti-viral innate immune responses and the pathogenesis of autoimmune diseases, they are subjected to manifold spatial and temporal modulations shaping the strength and duration of the signaling pathways. Recent progress has characterized the cyclic GMP-AMP synthase (cGAS) as the primary DNA sensor that initiates stimulator of interferon genes (STING)-dependent signaling pathway. However, it remains poorly understood how cGAS activity is modulated dynamically. In this study, we identify E3 ubiquitin ligase RNF185 as a positive regulator of cGAS-STING signaling. Knockdown of RNF185 significantly attenuates IRF3-responsive gene expression. ER-resident RNF185 interacts with cGAS and catalyzes the K27-linked poly-ubiquitination of cGAS upon HSV-1 challenges, which thus potentiates cGAS enzymatic activity. Notably, systemic lupus erythematosus (SLE) patients have elevated expression of RNF185 mRNA. Our study uncovers RNF185 as the first E3 ubiquitin ligase of cGAS and suggests RNF185 as an important target for modulating antiviral response.

High-dose dexamethasone (DEX) is used to treat chemotherapy-induced nausea and vomiting or to control immunotherapy-related autoimmune diseases in clinical practice. However, the underlying mechanisms of high-dose DEX in tumor progression remain unaddressed. Therefore, we explored the effects of high-dose DEX on tumor progression and the potential mechanisms of its anti-tumor function using immunohistochemistry, histological examination, real-time quantitative PCR (qPCR), and Western blotting. Tumor volume, blood vessel invasion, and levels of the cell proliferation markers Ki67 and c-Myc and the anti-apoptotic marker Bcl2 decreased in response to high-dose DEX. However, the cell apoptosis marker cleaved caspase 3 increased significantly in mice treated with 50 mg/kg DEX compared with controls. Some genes associated with immune responses were significantly downregulated following treatment with 50 mg/kg DEX e.g., Cxcl9, Cxcl10, Cd3e, Gzmb, Ifng, Foxp3, S100a9, Arg1, and Mrc1. In contrast, the M1-like tumor-associated macrophages (TAMs) activation marker Nos2 was shown to be increased. Moreover, the expression of peroxisome proliferator-activated receptors α and γ (Pparα and Pparg, respectively) was shown to be significantly upregulated in livers or tumors treated with DEX. However, high-dose DEX treatment decreased the expression of glucose and lipid metabolic pathway-related genes such as glycolysis-associated genes (Glut1, Hk2, Pgk1, Idh3a), triglyceride (TG) synthesis genes (Gpam, Agpat2, Dgat1), exogenous free fatty acid (FFA) uptake-related genes (Fabp1, Slc27a4, and CD36), and fatty acid oxidation (FAO) genes (Acadm, Acaa1, Cpt1a, Pnpla2). In addition, increased serum glucose and decreased serum TG and non-esterified fatty acid (NEFA) were observed in DEX treated-xenografted tumor mice. These findings indicate that high-dose DEX-inhibited tumor progression is a complicated process, not only activated by M1-like TAMs, but also decreased by the uptake and consumption of glucose and lipids that block the raw material and energy supply of cancer cells. Activated M1-like TAMs and inefficient glucose and lipid metabolism delayed tumor cell growth and promoted apoptosis. These findings have important implications for the application of DEX combined with drugs that target key metabolism pathways for tumor therapy in clinical practice.

Tight junctions are crucial for maintaining intestinal barrier homeostasis, but how organisms modulate these junctions remain unclear. Here, we show a role for PEAK1 at cell-cell contact sites, where it interacts with ZO-1 via a conserved region spanning amino acids 714-731. This interaction masks the LC3-interacting region on ZO-1, preventing autophagy-mediated ZO-1 degradation and preserving the integrity of tight junctions in intestinal epithelial cells. Src-mediated phosphorylation of PEAK1 at Y724 promotes the binding between PEAK1 and ZO-1 to stabilize ZO-1 in intestinal epithelial cells. Additionally, PEAK1 binds to CSK to positively regulate Src activity. Loss of PEAK1 in intestinal epithelial cells leads to decreased Src activity and lower ZO-1 protein levels, resulting in disrupted tight junctions, both in vitro and in vivo. In mice, Peak1 deficiency increases intestinal epithelium permeability and exacerbates inflammation in experimentally induced colitis models. Our findings reveal PEAK1’s critical role in maintaining tight junction integrity and resistance to intestinal inflammation, extending its known function from promoting tumor cell proliferation and migration to essential physiological processes. These insights refine our understanding of the mechanisms regulating tight junctions and offer potential therapeutic targets for enhancing epithelial barrier function and treating related diseases.

The renal tubules, which have distant metabolic features and functions in different segments, reabsorb >99% of approximately 180 l of water and 25,000 mmol of Na + daily. Defective metabolism in renal tubules is involved in the pathobiology of kidney diseases. However, the mechanisms underlying the metabolic regulation in renal tubules remain to be defined. We quantitatively compared the proteomes of the isolated proximal tubules (PT) and distal tubules (DT) from C57BL/6 mouse using tandem mass tag (TMT) labeling-based quantitative mass spectrometry. Bioinformatics analysis of the differentially expressed proteins revealed the significant differences between PT and DT in metabolism pathway. We also performed in vitro and in vivo assays to investigate the molecular mechanism underlying the distant metabolic features in PT and DT. We demonstrate that the renal proximal tubule (PT) has high expression of lipid metabolism enzymes, which is transcriptionally upregulated by abundantly expressed PPARα/γ. In contrast, the renal distal tubule (DT) has elevated glycolytic enzyme expression, which is mediated by highly expressed c-Myc. Importantly, PPARγ transcriptionally enhances the protease iRhom2 expression in PT, which suppresses EGF expression and secretion and subsequent EGFR-dependent glycolytic gene expression and glycolysis. PPARγ inhibition reduces iRhom2 expression and increases EGF and GLUT1 expression in PT in mice, resulting in renal tubule hypertrophy, tubulointerstitial fibrosis and damaged kidney functions, which are rescued by 2-deoxy-d-glucose treatment. These findings delineate instrumental mechanisms underlying the active lipid metabolism and suppressed glycolysis in PT and active glycolysis in DT and reveal critical roles for PPARs and c-Myc in maintaining renal metabolic homeostasis. FUND: This work was supported by the National Natural Science Foundation of China (grants 81572076 and 81873932; to Q.Z.), the Applied Development Program of the Science and Technology Committee of Chongqing (cstc2014yykfB10003; Q.Z.), the Program of Populace Creativities Workshops of the Science and Technology Committee of Chongqing (Q.Z.), the special demonstration programs for innovation and application of techniques (cstc2018jscx-mszdX0022) from the Science and Technology Committee of Chongqing (Q.Z.).