Identifying USPs regulating immune signals in Drosophila: USP2 deubiquitinates Imd and promotes its degradation by interacting with the proteasome.

International audienceBACKGROUND: Rapid activation of innate immune defences upon microbial infection depends on the evolutionary conserved NF-κB dependent signals which deregulation is frequently associated with chronic inflammation and oncogenesis. These signals are tightly regulated by the linkage of different kinds of ubiquitin moieties on proteins that modify either their activity or their stability. To investigate how ubiquitin specific proteases (USPs) orchestrate immune signal regulation, we created and screened a focused RNA interference library on Drosophila NF-κB-like pathways Toll and Imd in cultured S2 cells, and further analysed the function of selected genes in vivo. RESULTS: We report here that USP2 and USP34/Puf, in addition to the previously described USP36/Scny, prevent inappropriate activation of Imd-dependent immune signal in unchallenged conditions. Moreover, USP34 is also necessary to prevent constitutive activation of the Toll pathway. However, while USP2 also prevents excessive Imd-dependent signalling in vivo, USP34 shows differential requirement depending on NF-κB target genes, in response to fly infection by either Gram-positive or Gram-negative bacteria. We further show that USP2 prevents the constitutive activation of signalling by promoting Imd proteasomal degradation. Indeed, the homeostasis of the Imd scaffolding molecule is tightly regulated by the linkage of lysine 48-linked ubiquitin chains (K48) acting as a tag for its proteasomal degradation. This process is necessary to prevent constitutive activation of Imd pathway in vivo and is inhibited in response to infection. The control of Imd homeostasis by USP2 is associated with the hydrolysis of Imd linked K48-ubiquitin chains and the synergistic binding of USP2 and Imd to the proteasome, as evidenced by both mass-spectrometry analysis of USP2 partners and by co-immunoprecipitation experiments. CONCLUSION: Our work identified one known (USP36) and two new (USP2, USP34) ubiquitin specific proteases regulating Imd or Toll dependent immune signalling in Drosophila. It further highlights the ubiquitin dependent control of Imd homeostasis and shows a new activity for USP2 at the proteasome allowing for Imd degradation. This study provides original information for the better understanding of the strong implication of USP2 in pathological processes in humans, including cancerogenesis

Distinct roles of Hoxa2 and Krox20 in the development of rhythmic neural networks controlling inspiratory depth, respiratory frequency, and jaw opening

<p>Abstract</p> <p>Background</p> <p>Little is known about the involvement of molecular determinants of segmental patterning of rhombomeres (r) in the development of rhythmic neural networks in the mouse hindbrain. Here, we compare the phenotypes of mice carrying targeted inactivations of <it>Hoxa2</it>, the only <it>Hox </it>gene expressed up to r2, and of <it>Krox20</it>, expressed in r3 and r5. We investigated the impact of such mutations on the neural circuits controlling jaw opening and breathing in newborn mice, compatible with Hoxa2-dependent trigeminal defects and direct regulation of <it>Hoxa2 </it>by Krox20 in r3.</p> <p>Results</p> <p>We found that <it>Hoxa2 </it>mutants displayed an impaired oro-buccal reflex, similarly to <it>Krox20 </it>mutants. In contrast, while <it>Krox20 </it>is required for the development of the rhythm-promoting parafacial respiratory group (pFRG) modulating respiratory frequency,<it> Hoxa2 </it>inactivation did not affect neonatal breathing frequency. Instead, we found that <it>Hoxa2</it>^-/-but not <it>Krox20</it>^-/-mutation leads to the elimination of a transient control of the inspiratory amplitude normally occurring during the first hours following birth. Tracing of r2-specific progenies of <it>Hoxa2 </it>expressing cells indicated that the control of inspiratory activity resides in rostral pontine areas and required an intact r2-derived territory.</p> <p>Conclusion</p> <p>Thus, inspiratory shaping and respiratory frequency are under the control of distinct <it>Hox</it>-dependent segmental cues in the mammalian brain. Moreover, these data point to the importance of rhombomere-specific genetic control in the development of modular neural networks in the mammalian hindbrain.</p

A functional endosomal pathway is necessary for lysosome biogenesis in Drosophila

BACKGROUND: Lysosomes are the major catabolic compartment within eukaryotic cells, and their biogenesis requires the integration of the biosynthetic and endosomal pathways. Endocytosis and autophagy are the primary inputs of the lysosomal degradation pathway. Endocytosis is specifically needed for the degradation of membrane proteins whereas autophagy is responsible for the degradation of cytoplasmic components. We previously identified the deubiquitinating enzyme UBPY/USP8 as being necessary for lysosomal biogenesis and productive autophagy in Drosophila. Because UBPY/USP8 has been widely described for its function in the endosomal system, we hypothesized that disrupting the endosomal pathway itself may affect the biogenesis of the lysosomes. RESULTS: In the present study, we blocked the progression of the endosomal pathway at different levels of maturation of the endosomes by expressing in fat body cells either dsRNAs or dominant negative mutants targeting components of the endosomal machinery: Shibire, Rab4, Rab5, Chmp1 and Rab7. We observed that inhibition of endosomal trafficking at different steps in vivo is systematically associated with defects in lysosome biogenesis, resulting in autophagy flux blockade. CONCLUSION: Our results show that the integrity of the endosomal system is required for lysosome biogenesis and productive autophagy in vivo

The <b><i>Drosophila</i></b> Deubiquitinating Enzyme dUSP36 Acts in the Hemocytes for Tolerance to <b><i>Listeria monocytogenes</i></b> Infections

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Deubiquitinating Enzymes Related to Autophagy: New Therapeutic Opportunities?

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Additional file 1: Figure S1. of A functional endosomal pathway is necessary for lysosome biogenesis in Drosophila

The FLPout system in Drosophila. (A-B) The recombination between FRT sites by the FLP recombinase under the control of a heat shock promoter (A) results in excision of the CD2- STOP cassette and expression of GAL4 (B) which in turn activates the expression of the transgenes downstream the UAS promoter, including a fluorescent reporter (GFP, or GFP-tagged protein). No recombination between the FRT leaves the CD2-STOP cassette in place, thus preventing GAL4 expression (C). (TIF 676 kb

Additional file 3: Figure S3. of A functional endosomal pathway is necessary for lysosome biogenesis in Drosophila

Validation of defects in the endosomal pathway by Texas Red-Avidin uptake. (A-B) The endocytic tracer TR-avidin fails to be internalized in clonal cells expressing either ShiK44A (A) or Rab5-IR (B). Clones were detected by the co-expression of the autophagy marker GFP-Atg8a. (C-G) Internalized TR-avidin fails to be transported to the lysosomes when late stages of the endocytic process are defective. Clonal cells were detected by the expression of the lysosomal marker GFP-LAMP1. Occasional colocalization between the endocytic tracer TR-avidin and the lysosomes are observed in control cells (D) but not in cells expressing Rab4SN (E), Chmp1-IR (F) or Rab7TN (G). Quantification of the colocalization between the TR-avidin and GFP-LAMP1 using the Pearson’s Correlation Coefficient (PCC) is shown in C. Bars denote mean ± s.d. Statistical significance was determined using one-way ANOVA: *p < 0.05, **p < 0.005, ***p < 0.0005, ****p < 0.0001. Genotypes: (A) y w hs-FLP/UAS-ShiK44A; UAS-GFP-Atg8a/+; Ac > CD2 > Gal4/ UAS-ShiK44A, (B) y w hs-FLP/+; UAS-GFP-Atg8a/+; Ac > CD2 > Gal4/UAS-Rab5-IR, (C) y w hs-FLP/+; UAS-GFP-LAMP1/+; Ac > CD2 > Gal4/+, (D) y w hs-FLP/+; UAS-GFP-LAMP1/+; Ac > CD2 > Gal4/UAS-Rab4SN, (E) y w hs-FLP/+; UAS-GFP-LAMP1/+; Ac > CD2 > Gal4/UAS-Chmp1-IR, (F) y w hs-FLP/+; UAS-GFP-LAMP1/UAS-Rab7TN; Ac > CD2 > Gal4/+. (TIF 1831 kb

A Nucleolar Isoform of the Drosophila Ubiquitin Specific Protease dUSP36 Regulates MYC-Dependent Cell Growth

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The bacterial toxin ExoU requires a host trafficking chaperone for transportation and to induce necrosis

International audienceAbstract Pseudomonas aeruginosa can cause nosocomial infections, especially in ventilated or cystic fibrosis patients. Highly pathogenic isolates express the phospholipase ExoU, an effector of the type III secretion system that acts on plasma membrane lipids, causing membrane rupture and host cell necrosis. Here, we use a genome-wide screen to discover that ExoU requires DNAJC5, a host chaperone, for its necrotic activity. DNAJC5 is known to participate in an unconventional secretory pathway for misfolded proteins involving anterograde vesicular trafficking. We show that DNAJC5-deficient human cells, or Drosophila flies knocked-down for the DNAJC5 orthologue, are largely resistant to ExoU-dependent virulence. ExoU colocalizes with DNAJC5-positive vesicles in the host cytoplasm. DNAJC5 mutations preventing vesicle trafficking (previously identified in adult neuronal ceroid lipofuscinosis, a human congenital disease) inhibit ExoU-dependent cell lysis. Our results suggest that, once injected into the host cytoplasm, ExoU docks to DNAJC5-positive secretory vesicles to reach the plasma membrane, where it can exert its phospholipase activit