Immunity-related GTPase M (IRGM) proteins influence the localization of guanylate-binding protein 2 (GBP2) by modulating macroautophagy

The immunity-related GTPases (IRGs) are a family of proteins induced by interferon-γ that play a crucial role in innate resistance to intracellular pathogens. The M subfamily of IRG proteins (IRGM) plays a profound role in this context, in part because of the ability of its members to regulate the localization and expression of other IRG proteins. We present here evidence that IRGM proteins affect the localization of the guanylate-binding proteins (GBPs), a second family of interferon-induced GTP-binding proteins that also function in innate immunity. Absence of Irgm1 or Irgm3 led to accumulation of Gbp2 in intracellular compartments that were positive for both the macroautophagy (hereafter referred to as autophagy) marker LC3 and the autophagic adapter molecule p62/Sqstm1. Gbp2 was similarly relocalized in cells in which autophagy was impaired because of the absence of Atg5. Both in Atg5- and IRGM-deficient cells, the IRG protein Irga6 relocalized to the same compartments as Gbp2, raising the possibility of a common regulatory mechanism. However, other data indicated that Irga6, but not Gbp2, was ubiquitinated in IRGM-deficient cells. Similarly, coimmunoprecipitation studies indicated that although Irgm3 did interact directly with Irgb6, it did not interact with Gbp2. Collectively, these data suggest that IRGM proteins indirectly modulate the localization of GBPs through a distinct mechanism from that through which they regulate IRG protein localization. Further, these results suggest that a core function of IRGM proteins is to regulate autophagic flux, which influences the localization of GBPs and possibly other factors that instruct cell-autonomous immune resistance.     

Green‐wave surfing increases fat gain in a migratory ungulate

Each spring, migratory herbivores around the world track or ‘surf’ green waves of newly emergent vegetation to distant summer or wet‐season ranges. This foraging tactic may help explain the great abundance of migratory herbivores on many seasonal landscapes. However, the underlying fitness benefits of this life‐history strategy remain poorly understood. A fundamental prediction of the green‐wave hypothesis is that migratory herbivores obtain fitness benefits from surfing waves of newly emergent vegetation more closely than their resident counterparts. Here we evaluate whether this behavior increases body‐fat levels – a critically important correlate of reproduction and survival for most ungulates – in elk Cervus elaphus of the Greater Yellowstone Ecosystem. Using satellite imagery and GPS tracking data, we found evidence that migrants (n = 23) indeed surfed the green wave, occupying sites 12.7 days closer to peak green‐up than residents (n = 16). Importantly, individual variation in surfing may help account for up to 6 kg of variation in autumn body‐fat levels. Our findings point to a pathway for anthropogenic changes to the green wave (e.g. climate change) or migrants’ ability to surf it (e.g. development) to impact migratory populations. To explore this possibility, we evaluated potential population‐level consequences of constrained surfing with a heuristic model. If green‐wave surfing deteriorates by 5–15 days from observed, our model predicts up to a 20% decrease in pregnancy rates, a 2.5% decrease in population growth, and a 30% decrease in abundance over 50 years. By linking green‐wave surfing to fitness and illustrating potential effects on population growth, our study provides new insights into the evolution of migratory behavior and the prospects for the persistence of migratory ungulate populations in a changing world.     

How Mitochondrial Metabolism Contributes to Macrophage Phenotype and Functions

Metabolic reprogramming of cells from the innate immune system is one of the most noteworthy topics in immunological research nowadays. Upon infection or tissue damage, innate immune cells, such as macrophages, mobilize various immune and metabolic signals to mount a response best suited to eradicate the threat. Current data indicate that both the immune and metabolic responses are closely interconnected. On account of its peculiar position in regulating both of these processes, the mitochondrion has emerged as a critical organelle that orchestrates the coordinated metabolic and immune adaptations in macrophages. Significant effort is now underway to understand how metabolic features of differentiated macrophages regulate their immune specificities with the eventual goal to manipulate cellular metabolism to control immunity. In this review, we highlight some of the recent work that place cellular and mitochondrial metabolism in a central position in the macrophage differentiation program.     

Studies on submaxillary gland immunoreactive glucagon.

Biologically active immunoreactive glucagon is present in submaxillary gland of rat, mouse, guinea pig and human and can be extracted by saline adjusted to pH 2.8 with HCl. Chromatography on Sephadex G-150 indicates its molecular weight to be 29,000. It has similar immunologic characteristics as pancreatic glucagon. It is biologically active and elevates plasma glucose and insulin when injected intraperitoneally into rats. Compared to pancreatic glucagon, the hyperglycemic effect persists much longer. It competes with pancreatic glucagon for binding to specific glucagon receptors of rat liver plasma membranes. It is stable to pH changes, however, urea dissociates it into several smaller molecular weight fragments including that of 3500. It appears to be an aggregate of smaller glucagon molecules and is not responsible for immunoreactive glucagon in totally eviscerated rats. $\text{In vitro}$, the submaxillary gland does not release immunoreactive glucagon in response to arginine or glucose.     

Upregulation of immunity-related GTPase (IRG) proteins by TNF-α in murine astrocytes

We examined the effect of tumor necrosis factor-alpha (TNF-α) on murine primary astrocytes. Proteomic analysis demonstrated that four new spots in the TNF-α-treated cells relative to untreated cells. Two of them were identified as Irgb6 and Irgd, members of immunity-related GTPase (IRG) proteins which are the key mediators of interferon-gamma (IFN-γ)-induced resistance of pathogens in numerous cells. Gene expression analysis using RT-PCR showed that TNF-α dose-dependently increased the expression of both proteins. Immunocytochemical analysis showed that TNF-α increased the abundance of both proteins. A subcellular localization study demonstrated that TNF-α induced the partial colocalization of both proteins with the endoplasmic reticulum (ER) and Golgi apparatus, whereas IFN-γ did not induce the colocalization of Irgd protein with the ER and Golgi. Combined stimulation with TNF-α and IFN-γ had a synergistic effect on the expression of Irgb6 and an added effect on the expression of Irgd.     

Expression pattern of XIRG, a marker for non-neural ectoderm

XIRG (for Xenopus IRG) was cloned by screening a cDNA library of UV-ventralized stage 13 Xenopus laevis embryos for specifically ventrally expressed mRNAs. Embryonic XIRG mRNA expression is restricted to non-neural ectoderm at the gastrula and neurula stages. In adult X. laevis, XIRG mRNA can be detected in skin and kidney. Extensive searches in nucleic acid and protein databases revealed homologous sequences in mouse, human and zebrafish. Mouse IRG1 mRNA is expressed in cultured macrophages as a response to bacterial lipopolysaccharide treatment. Received: 27 April 2000 / Accepted: 13 June 2000     

Targeting by AutophaGy proteins (TAG): Targeting of IFNG-inducible GTPases to membranes by the LC3 conjugation system of autophagy

LC3 has been used as a marker to locate autophagosomes. However, it is also well established that LC3 can localize on various membranous structures other than autophagosomes. We recently demonstrated that the LC3 conjugation system (ATG7, ATG3, and ATG12–ATG5-ATG16L1) is required to target LC3 and IFNG (interferon, gamma)-inducible GTPases to the parasitophorus vacuole membrane (PVM) of a protist parasite Toxoplasma gondii and consequently for IFNG to control T. gondii infection. Here we show that not only LC3, but also its homologs (GABARAP, GABARAPL1, and GABARAPL2) localize on the PVM of T. gondii in a conjugation-dependent manner. Knockout/knockdown of all LC3 homologs led to a significant reduction in targeting of the IFNG-inducible GTPases to the PVM of T. gondii and the IFNG-mediated control of T. gondii infection. Furthermore, when we relocated the ATG12–ATG5-ATG16L1 complex, which specifies the conjugation site of LC3 homologs, to alternative target membranes, the IFNG-inducible GTPases were targeted to the new target membranes rather than the PVM of T. gondii. These data suggest that the localization of LC3 homologs onto a membrane by the LC3 conjugation system is necessary and sufficient for targeting of the IFNG-inducible GTPases to the membrane, implying Targeting by AutophaGy proteins (TAG). Our data further suggest that the conjugation of ubiquitin-like LC3 homologs to the phospholipids of membranes may change the destiny of the membranes beyond degradation through lysosomal fusion, as the conjugation of ubiquitin to proteins changes the destiny of the proteins beyond proteasomal degradation.     

4-octyl itaconate as a metabolite derivative inhibits inflammation via alkylation of STING

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