Proteasome α6 Subunit Negatively Regulates the JAK/STAT Pathway and Blood Cell Activation in Drosophila melanogaster

JAK/STAT signaling regulates central biological functions such as development, cell differentiation and immune responses. In Drosophila, misregulated JAK/STAT signaling in blood cells (hemocytes) induces their aberrant activation. Using mass spectrometry to analyze proteins associated with a negative regulator of the JAK/STAT pathway, and by performing a genome-wide RNAi screen, we identified several components of the proteasome complex as negative regulators of JAK/STAT signaling in Drosophila. A selected proteasome component, Prosα6, was studied further. In S2 cells, Prosα6 silencing decreased the amount of the known negative regulator of the pathway, ET, leading to enhanced expression of a JAK/STAT pathway reporter gene. Silencing of Prosα6 in vivo resulted in activation of the JAK/STAT pathway, leading to the formation of lamellocytes, a specific hemocyte type indicative of hemocyte activation. This hemocyte phenotype could be partially rescued by simultaneous knockdown of either the Drosophila STAT transcription factor, or MAPKK in the JNK-pathway. Our results suggest a role for the proteasome complex components in the JAK/STAT pathway in Drosophila blood cells both in vitro and in vivo.

Osa-Containing Brahma Complex Regulates Innate Immunity and the Expression of Metabolic Genes in Drosophila

Negative regulation of innate immunity is essential to avoid autoinflammation. In Drosophila melanogaster, NF-κB signaling-mediated immune responses are negatively regulated at multiple levels. Using a Drosophila RNA interference in vitro screen, we identified a set of genes inhibiting immune activation. Four of these genes encode members of the chromatin remodeling Osa-containing Brahma (BAP) complex. Silencing additional two genes of the BAP complex was shown to have the same phenotype, confirming its role in immune regulation in vitro. In vivo, the knockdown of osa and brahma was shown to enhance the expression of the Toll pathway-mediated antimicrobial peptides when the flies were challenged with Gram-positive bacteria Micrococcus luteus In this setting, osa knockdown had a particularly strong effect on immune effectors that are predominantly activated by the Imd pathway. Accordingly, Drosophila NF-κB Relish expression was increased by osa silencing. These transcriptional changes were associated with enhanced survival from M. luteus + E. faecalis infection. Besides regulating the expression of immune effector genes, osa RNA interference decreased the expression of a large group of genes involved in metabolism, particularly proteolysis. Of note, the expression of the recently characterized, immune-inducible gene Induced by Infection (IBIN) was diminished in osa knockdown flies. Although IBIN has been shown to modulate metabolism upon infection, the expression of selected Osa-regulated metabolism genes was not rescued by overexpressing IBIN. We conclude that the BAP complex regulates expression of genes involved in metabolism at least partially independent or downstream of IBIN Moreover, Osa affects the NF-κB-mediated immune response by regulating Drosophila NF-κB factor Relish expression.

Correction: Immune-inducible non-coding RNA molecule lincRNA-IBIN connects immunity and metabolism in Drosophila melanogaster

[This corrects the article DOI: 10.1371/journal.ppat.1007504.].

Immune-inducible non-coding RNA molecule lincRNA-IBIN connects immunity and metabolism in Drosophila melanogaster

Non-coding RNAs have important roles in regulating physiology, including immunity. Here, we performed transcriptome profiling of immune-responsive genes in Drosophila melanogaster during a Gram-positive bacterial infection, concentrating on long non-coding RNA (lncRNA) genes. The gene most highly induced by a Micrococcus luteus infection was CR44404, named Induced by Infection (lincRNA-IBIN). lincRNA-IBIN is induced by both Gram-positive and Gram-negative bacteria in Drosophila adults and parasitoid wasp Leptopilina boulardi in Drosophila larvae, as well as by the activation of the Toll or the Imd pathway in unchallenged flies. We show that upon infection, lincRNA-IBIN is expressed in the fat body, in hemocytes and in the gut, and its expression is regulated by NF-κB signaling and the chromatin modeling brahma complex. In the fat body, overexpression of lincRNA-IBIN affected the expression of Toll pathway -mediated genes. Notably, overexpression of lincRNA-IBIN in unchallenged flies elevated sugar levels in the hemolymph by enhancing the expression of genes important for glucose retrieval. These data show that lncRNA genes play a role in Drosophila immunity and indicate that lincRNA-IBIN acts as a link between innate immune responses and metabolism.