TFG is required for autophagy flux and to prevent endoplasmic reticulum stress in CH12 B lymphoma cells

TM9SF1 expression correlates with autoimmune disease activity and regulates antibody production through mTOR-dependent autophagy

BACKGROUND

Transmembrane 9 superfamily member 1 (TM9SF1) is involved in inflammation. Since both inflammatory and autoimmune diseases are linked to immune cells regulation, this study investigated the association between TM9SF1 expression and autoimmune disease activity. As B cell differentiation and autoantibody production exacerbate autoimmune disease, the signaling pathways involved in these processes were explored.

METHODS

Tm9sf1-/- mouse rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) models were used to verify the relationship between gene expression and disease severity. Peripheral blood mononuclear cells (PBMCs) from 156 RA and 145 SLE patients were used to explore the relationship between TM9SF1 expression and disease activity. The effectiveness of TM9SF1 as a predictor of disease activity was assessed using multiple logistic regression and receiver operating characteristic (ROC) curves. The signaling pathways regulated by TM9SF1 in B cell maturation and antibody production were conducted by plasma cell induction experiment in vitro.

RESULTS

The Tm9sf1-/- RA and SLE model mice produced fewer autoantibodies and showed reduced disease severity relative to wild-type (WT) mice. TM9SF1 levels in PBMCs of patients were higher than those in healthy controls, and were reduced in patients with low disease activity relative to those with active RA and SLE. Furthermore, TM9SF1 levels were positively linked with autoantibody titers and pro-inflammatory cytokine levels in both diseases. ROC analyses indicated TM9SF1 outperformed several important clinical indicators in predicting disease activity (area under the curve (AUC) were 0.858 and 0.876 for RA and SLE, respectively). In vitro experiments demonstrated that Tm9sf1 knockout blocked differentiation of B cells into antibody-producing plasma cells by activating mTOR and inhibiting autophagy, and mTOR inhibitors such as rapamycin could reverse this effect.

CONCLUSIONS

The primary finding was the identification of the molecular mechanism underlying autophagy regulation in B cells, in which Tm9sf1 knockout was found to modulate mTOR-dependent autophagy to block B cell differentiation into antibody-secreting plasma cells. It was also found that TM9SF1 expression level in PBMCs was an accurate indicator of disease activity in patients with RA and SLE, suggesting its clinical potential for monitoring disease activity in these patients.

TFG regulates inner COPII coat recruitment to facilitate anterograde secretory protein transport

Coat protein complex II (COPII) governs the initial steps of biosynthetic secretory protein transport from the endoplasmic reticulum (ER), facilitating the movement of a wide variety of cargoes. Here, we demonstrate that Trk-fused gene (TFG) regulates the rate at which inner COPII coat proteins are concentrated at ER subdomains. Specifically, in cells lacking TFG, the GTPase-activating protein (GAP) Sec23 accumulates more rapidly at budding sites on the ER as compared with control cells, potentially altering the normal timing of GTP hydrolysis on Sar1. Under these conditions, anterograde trafficking of several secretory cargoes is delayed, irrespective of their predicted size. We propose that TFG controls the local, freely available pool of Sec23 during COPII coat formation and limits its capacity to prematurely destabilize COPII complexes on the ER. This function of TFG enables it to act akin to a rheostat, promoting the ordered recruitment of Sec23, which is critical for efficient secretory cargo export.

Nlp-dependent ER-to-Golgi transport

The mechanism that maintains ER-to-Golgi vesicles formation and transport is complicated. As one of the adapters, Ninein-like protein (Nlp) participated in assembly and transporting of partial ER-to-Golgi vesicles that contained specific proteins, such as β-Catenin and STING. Nlp acted as a platform to sustain the specificity and continuity of cargoes during COPII and COPI-coated vesicle transition and transportation through binding directly with SEC31A as well as Rab1B. Thus, we proposed an integrated transport model that particular adapter participated in specific cargo selection or transportation through cooperating with different membrane associated proteins to ensure the continuity of cargo trafficking. Deficiency of Nlp led to vesicle budding failure and accumulation of unprocessed proteins in ER, which further caused ER stress as well as Golgi fragmentation, and PERK-eIF2α pathway of UPR was activated to reduce the synthesis of universal proteins. In contrast, upregulation of Nlp resulted in Golgi fragmentation, which enhanced the cargo transport efficiency between ER and Golgi. Moreover, Nlp deficient mice were prone to spontaneous B cell lymphoma, since the developments and functions of lymphocytes significantly depended on secretory proteins through ER-to-Golgi vesicle trafficking, including IL-13, IL-17 and IL-21. Thus, perturbations of Nlp altered ER-to-Golgi communication and cellular homeostasis, and might contribute to the pathogenesis of B cell lymphoma.

Identification of TFG- and Autophagy-Regulated Proteins and Glycerophospholipids in B Cells

Autophagy supervises the proteostasis and survival of B lymphocytic cells. Trk-fused gene (TFG) promotes autophagosome-lysosome flux in murine CH12 B cells, as well as their survival. Hence, quantitative proteomics of CH12tfgKO and WT B cells in combination with lysosomal inhibition should identify proteins that are prone to lysosomal degradation and contribute to autophagy and B cell survival. Lysosome inhibition via NH4Cl unexpectedly reduced a number of proteins but increased a large cluster of translational, ribosomal, and mitochondrial proteins, independent of TFG. Hence, we propose a role for lysosomes in ribophagy in B cells. TFG-regulated proteins include CD74, BCL10, or the immunoglobulin JCHAIN. Gene ontology (GO) analysis reveals that proteins regulated by TFG alone, or in concert with lysosomes, localize to mitochondria and membrane-bound organelles. Likewise, TFG regulates the abundance of metabolic enzymes, such as ALDOC and the fatty acid-activating enzyme ACOT9. To test consequently for a function of TFG in lipid metabolism, we performed shotgun lipidomics of glycerophospholipids. Total phosphatidylglycerol is more abundant in CH12tfgKO B cells. Several glycerophospholipid species with similar acyl side chains, such as 36:2 phosphatidylethanolamine and 36:2 phosphatidylinositol, show a dysequilibrium. We suggest a role for TFG in lipid homeostasis, mitochondrial functions, translation, and metabolism in B cells.

Blockade of CXCR4 promotes macrophage autophagy through the PI3K/AKT/mTOR pathway to alleviate coronary heart disease

OBJECTIVE

Autophagy is important in regulating inflammation and cholesterol efflux, suggesting that targeting autophagy may slow down atherosclerosis (AS). Since the pathological basis of coronary artery disease (CAD) is atherosclerosis, it is crucial to investigate the role of autophagy in atherosclerosis. This study aimed to investigate the role of the chemokine CXC chemokine receptor 4 (CXCR4) in promoting macrophage autophagy through the phosphoinositide-3 kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway to alleviate coronary artery disease.

METHODS

The human left coronary artery and myocardium were collected to detect CXCR4, MAP1LC3(LC3) and SQSTM1(p62) expression. ApoE-/- mice were used to establish an atherosclerosis mice model, while human monocytes (THP-1) were used to establish a foam cell model and co-cultured with foam cells using siRNACXCR4. Western blotting was conducted to quantify CXCR4, PI3K/AKT/mTOR pathway protein, LC3, Beclin1 and p62 protein levels. The left coronary artery from humans and mouse aorta and myocardium were stained with Hematoxylin and Eosin (H&E), macrophages with Oil Red O staining and foam cells were assessed by Movat's staining. CXCR4 levels, PI3K/AKT/mTOR pathway protein, LC3 and p62 were detected by immunohistochemistry (IHC) and immunofluorescence assays. Detection of autophagosomes in macrophages using transmission electron microscopy. We further assessed whether the effect of CXCR4-mediated macrophage autophagy on the formation of atherosclerosis and structural changes in the myocardium was mediated via the PI3K/AKT/mTOR signaling pathway.

RESULTS

CXCR4 and p62 proteins were upregulated in human coronary lesions, mouse aorta, myocardial tissue, and foam cells, while LC3II/LC3I was downregulated. p85 (P-PI3K), Ser473 (P-AKT), and Ser2448 (P-mTOR) phosphorylated proteins associated with the PI3K/AKT/mTOR pathway were detected in AS and foam cell models. Upregulated CXCR4 inhibited autophagy of macrophages and increased the severity of atherosclerotic lesions. After specific knockdown of CXCR4 by adeno-associated virus (AAV9-CXCR4-RNAi) and siRNACXCR4, the above indicators were reversed, macrophage autophagy was promoted, the severity of atherosclerotic lesions was reduced, and the disorganized arrangement of myocardial architecture was improved.

CONCLUSION

Knockdown of CXCR4 reduces the extent of coronary artery disease by promoting macrophage autophagy through the PI3K/AKT/mTOR pathway to attenuate atherosclerosis.

Mitochondrial respiration in B lymphocytes is essential for humoral immunity by controlling the flux of the TCA cycle

To elucidate the function of oxidative phosphorylation (OxPhos) during B cell differentiation, we employ CD23Cre-driven expression of the dominant-negative K320E mutant of the mitochondrial helicase Twinkle (DNT). DNT-expression depletes mitochondrial DNA during B cell maturation, reduces the abundance of respiratory chain protein subunits encoded by mitochondrial DNA, and, consequently, respiratory chain super-complexes in activated B cells. Whereas B cell development in DNT mice is normal, B cell proliferation, germinal centers, class switch to IgG, plasma cell maturation, and T cell-dependent as well as T cell-independent humoral immunity are diminished. DNT expression dampens OxPhos but increases glycolysis in lipopolysaccharide and B cell receptor-activated cells. Lipopolysaccharide-activated DNT-B cells exhibit altered metabolites of glycolysis, the pentose phosphate pathway, and the tricarboxylic acid cycle and a lower amount of phosphatidic acid. Consequently, mTORC1 activity and BLIMP1 induction are curtailed, whereas HIF1α is stabilized. Hence, mitochondrial DNA controls the metabolism of activated B cells via OxPhos to foster humoral immunity.

Comparative Study of Autophagy in Oxaliplatin-Sensitive and Resistant SNU-C5 Colon Cancer Cells

Few studies have evaluated the role of autophagy in the development of oxaliplatin (OXT) resistance in colon cancer cells. In this study, we compared the role of autophagy between SNU-C5 colon cancer cells and OXT-resistant SNU-C5 (SNU-C5/OXTR) cells. At the same concentration of OXT, the cytotoxicity of OXT or apoptosis was significantly reduced in SNU-C5/OXTR cells compared with that in SNU-C5 cells. Compared with SNU-C5 cells, SNU-C5/OXTR cells exhibited low levels of autophagy. The expression level of important autophagy proteins, such as autophagy-related protein 5 (Atg5), beclin-1, Atg7, microtubule-associated proteins 1A/1B light chain 3B I (LC3-I), and LC3-II, was significantly lower in SNU-C5/OXTR cells than that in SNU-C5 cells. The expression level of the autophagy-essential protein p62 was also lower in SNU-C5/OXTR cells than in SNU-C5 cells. In SNU-C5/OXTR cells, the production of intracellular reactive oxygen species (ROS) was significantly higher than that in SNU-C5 cells, and treatment with the ROS scavenger N-acetylcysteine restored the reduced autophagy levels. Furthermore, the expression of antioxidant-related nuclear factor erythroid 2-related factor 2 transcription factor, heme oxygenase-1, and Cu/Zn superoxide dismutase were also significantly increased in SNU-C5/OXTR cells. These findings suggest that autophagy is significantly reduced in SNU-C5/OXTR cells compared with SNU-C5 cells, which may be related to the production of ROS in OXT-resistant cells.

TRK-fused gene (TFG) regulates ULK1 stability via TRAF3-mediated ubiquitination and protects macrophages from LPS-induced pyroptosis

TRK-fused gene (TFG) is known to be involved in protein secretion and plays essential roles in an antiviral innate immune response. However, its function in LPS-induced inflammation and pyroptotic cell death is still unknown. Here, we reported that TFG promotes the stabilization of Unc-51 like autophagy activating kinase (ULK1) and participates in LPS plus nigericin (Ng) induced pyroptotic cell death. Our results showed that TFG-deficient THP-1 macrophages exhibit higher mitochondrial ROS production. LPS/Ng stimulation triggers a much higher level of ROS and induces pyroptotic cell death. ULK1 undergoes a rapid turnover in TFG-deficient THP-1 cells. TFG forms complex with an E3 ligase, tumor necrosis factor receptor-associated factor 3 (TRAF3), and stabilizes ULK1 via disturbing ULK1-TRAF3 interaction. Knockdown of TFG facilitates the interaction of ULK1 with TRAF3 and subsequent K48-linked ULK1 ubiquitination and proteasome degradation. Rescue of ULK1 expression blocks LPS/Ng-induced cell death in TFG-deficient THP-1 macrophages. Taken together, TFG plays an essential role in LPS/Ng-induced pyroptotic cell death via regulating K48-linked ULK1 ubiquitination in macrophages.

Regulation of Endoplasmic Reticulum Stress-Autophagy: A Potential Therapeutic Target for Ulcerative Colitis

Ulcerative colitis (UC) is a chronic nonspecific inflammation that mainly affects the mucosa and submucosa of the rectum and colon. Numerous studies have shown that endoplasmic reticulum stress (ERS)-induced autophagy plays a vital role in the pathogenesis of UC. ERS is the imbalance of internal balance caused by misfolded or unfolded proteins accumulated in the endoplasmic reticulum (ER).Excessive ERS triggers the unfolded protein response (UPR), an increase in inositol-requiring enzyme 1, and a Ca²⁺ overload, which activates the autophagy pathway. Autophagy is an evolutionarily conserved method of cellular self-degradation. Dysregulated autophagy causes inflammation, disruption of the intestinal barrier, and imbalance of intestinal homeostasis, therefore increasing the risk of colonic diseases. This review summarizes the pathogenesis of ERS, UPR, and ERS-related autophagy in UC, providing potential new targets and more effective treatment options for UC.

Hereditary Spastic Paraplegia and Future Therapeutic Directions: Beneficial Effects of Small Compounds Acting on Cellular Stress

Hereditary spastic paraplegia (HSP) is a group of inherited neurodegenerative conditions that share a characteristic feature of degeneration of the longest axons within the corticospinal tract, which leads to progressive spasticity and weakness of the lower limbs. Mutations of over 70 genes produce defects in various biological pathways: axonal transport, lipid metabolism, endoplasmic reticulum (ER) shaping, mitochondrial function, and endosomal trafficking. HSPs suffer from an adequate therapeutic plan. Currently the treatments foreseen for patients affected by this pathology are physiotherapy, to maintain the outgoing tone, and muscle relaxant therapies for spasticity. Very few clinical studies have been conducted, and it's urgent to implement preclinical animal studies devoted to pharmacological test and screening, to expand the rose of compounds potentially attractive for clinical trials. Small animal models, such as Drosophila melanogaster and zebrafish, have been generated, analyzed, and used as preclinical model for screening of compounds and their effects. In this work, we briefly described the role of HSP-linked proteins in the organization of ER endomembrane system and in the regulation of ER homeostasis and stress as a common pathological mechanism for these HSP forms. We then focused our attention on the pharmacodynamic and pharmacokinetic features of some recently identified molecules with antioxidant property, such as salubrinal, guanabenz, N-acetyl cysteine, methylene blue, rapamycin, and naringenin, and on their potential use in future clinical studies. Expanding the models and the pharmacological screening for HSP disease is necessary to give an opportunity to patients and clinicians to test new molecules.

TFG binds LC3C to regulate ULK1 localization and autophagosome formation

The early secretory pathway and autophagy are two essential and evolutionarily conserved endomembrane processes that are finely interlinked. Although growing evidence suggests that intracellular trafficking is important for autophagosome biogenesis, the molecular regulatory network involved is still not fully defined. In this study, we demonstrate a crucial effect of the COPII vesicle-related protein TFG (Trk-fused gene) on ULK1 puncta number and localization during autophagy induction. This, in turn, affects formation of the isolation membrane, as well as the correct dynamics of association between LC3B and early ATG proteins, leading to the proper formation of both omegasomes and autophagosomes. Consistently, fibroblasts derived from a hereditary spastic paraparesis (HSP) patient carrying mutated TFG (R106C) show defects in both autophagy and ULK1 puncta accumulation. In addition, we demonstrate that TFG activity in autophagy depends on its interaction with the ATG8 protein LC3C through a canonical LIR motif, thereby favouring LC3C-ULK1 binding. Altogether, our results uncover a link between TFG and autophagy and identify TFG as a molecular scaffold linking the early secretion pathway to autophagy.

Wnt/β-catenin signaling: Structure, assembly and endocytosis of the signalosome

Wnt/β‐catenin signaling is an ancient pathway that regulates key aspects of embryonic development, cell differentiation, proliferation, and adult stem cell homeostasis. Work from different laboratories has shed light on the molecular mechanisms underlying the Wnt pathway, including structural details of ligand–receptor interactions. One key aspect that has emerged from multiple studies is that endocytosis of the receptor complex plays a crucial role in fine‐tuning Wnt/β‐catenin signaling. Endocytosis is a key process involved in both activation as well as attenuation of Wnt signaling, but how this is regulated is still poorly understood. Importantly, recent findings show that Wnt also regulates central metabolic pathways such as the acquisition of nutrients through actin‐driven endocytic mechanisms. In this review, we propose that the Wnt pathway displays diverse characteristics that go beyond the regulation of gene expression, through a connection with the endocytic machinery.