Endotoxin Substrate

Ubiquitylation is a widespread post-translational protein modification in eukaryotes and marks bacteria that invade the cytosol as cargo for antibacterial autophagy1-3. The identity of the ubiquitylated substrate on bacteria is unknown. Here we show that the ubiquitin coat on Salmonella that invade the cytosol is formed through the ubiquitylation of a non-proteinaceous substrate, the lipid A moiety of bacterial lipopolysaccharide (LPS), by the E3 ubiquitin ligase ring finger protein 213 (RNF213). RNF213 is a risk factor for moyamoya disease4,5, which is a progressive stenosis of the supraclinoid internal carotid artery that causes stroke (especially in children)6,7. RNF213 restricts the proliferation of cytosolic Salmonella and is essential for the generation of the bacterial ubiquitin coat, both directly (through the ubiquitylation of LPS) and indirectly (through the recruitment of LUBAC, which is a downstream E3 ligase that adds M1-linked ubiquitin chains onto pre-existing ubiquitin coats8). In cells that lack RNF213, bacteria do not attract ubiquitin-dependent autophagy receptors or induce antibacterial autophagy. The ubiquitylation of LPS on Salmonella that invade the cytosol requires the dynein-like core of RNF213, but not its RING domain. Instead, ubiquitylation of LPS relies on an RZ finger in the E3 shell. We conclude that ubiquitylation extends beyond protein substrates and that ubiquitylation of LPS triggers cell-autonomous immunity, and we postulate that non-proteinaceous substances other than LPS may also become ubiquitylated.

Macrophages settle in heterogeneous microenvironments rendered by other cells and extracellular matrices. It is well known that chemical stimuli direct macrophage behavior; however, the contributions of viscosity, which increases in inflammatory tissues but not in tumors, are ignored in immune responses including effective activation and timely attenuation. This paper demonstrates that transient lipopolysaccharide (LPS)-treated macrophages benefit from elastic substrates, whereas viscoelastic substrates with similar storage moduli support the inflammatory responses of macrophages under persistent stimulations and consequently amplify the distinctions between the transient and persistent LPS-induced transcriptional programs. Actin filaments (F-actin) fluctuate in line with transcriptional profiles and can be mathematically predicted by a clutch-like model. Moreover, viscosity modifies immune responses through transcription factors NF-κB and C/EBPδ, which act as switches discriminating transient and persistent infections. Interestingly, enhanced immune responses, consistent with the lower activated states, are attenuated promptly by the actin nucleation-related translocation of ATF3 to nuclei. These findings suggest that the substrate viscoelasticity induces more intense inflammation only in the case of persistent infection and promotes more sensitively perceiving the duration of infection through the F-actin correlated transcription factors. In addition, it may facilitate the cognition of immune response in inflammatory and cancerous microenvironments and have a wide range of applications in inflammatory regulations.

Since the first report by Ishiwata in 1902 of a Bombyx mori infection, followed by the description by Berliner, Bacillus thuringiensis (Bt) has become the main microorganism used in biological control. The application of Bt to combat invertebrates of human interest gained momentum with the growing demand for food free of chemical pesticides and with the implementation of agriculture methods that were less damaging to the environment. However, the mechanisms of action of these products have not been fully elucidated. There are two proposed models: the first is that Bt causes an osmotic imbalance in response to the formation of pores in a cell membrane, and the second is that it causes an opening of ion channels that activate the process of cell death. There are various ways in which Bt resistance can develop: changes in the receptors that do not recognize the Cry toxin, the synthesis of membrane transporters that eliminate the peptides from the cytosol and the development of regulatory mechanisms that disrupt the production of toxin receptors. Besides the potential for formulation of biopesticides and the use in developing genetically modified cultivars, recent studies with Bt have discussed promising applications in other branches of science. Chitinase, an enzyme that degrades chitin, increases the efficiency of Bt insecticides, and there has been of increasing interest in the industry, given that its substrate is extremely abundant in nature. Another promising field is the potential for Bt proteins to act against cancer cells. Parasporins, toxins of Bt that do not have an entomopathogenic effect, have a cytotoxic effect on the cells changed by some cancers. This demonstrates the potential of the microorganism and new opportunities opening for future applications.