Innate immunity mediated by Toll signalling has been extensively studied, but how Toll signalling is precisely controlled in balancing innate immune responses remains poorly understood. It was reported that the plasma membrane localization of Drosophila MyD88 is necessary for the recruitment of cytosolic adaptor Tube to the cell surface, thus contributing to Toll signalling transduction. Here we demonstrate that Drosophila Pellino functions as a negative regulator in Toll-mediated signalling. We show that Pellino accumulates at the plasma membrane upon the activation of Toll signalling in a MyD88-dependent manner. Moreover, we find that Pellino is associated with MyD88 via its CTE domain, which is necessary and sufficient to promote Pellino accumulation at the plasma membrane where it targets MyD88 for ubiquitination and degradation. Collectively, our study uncovers a mechanism by which a feedback regulatory loop involving MyD88 and Pellino controls Toll-mediated signalling, thereby maintaining homeostasis of host innate immunity.

Significance: Previous studies have demonstrated that Bam protein plays a critical role promoting early germ-line cell differentiation in the Drosophila ovary. Although its regulation and genetic functions have been extensively investigated over the last 20 years, the biochemical nature of Bam has still remained elusive. Here, we show that Bam functions as an ubiquitin-associated protein and regulates the stability of CycA. Our study uncovers a mechanism by which Bam functions as an ubiquitin-associated protein, and cooperates with Otu to deubiquitinate and stabilize CycA, thereby balancing GSC self-renewal and differentiation.

Significance: Inhibitory Smads (I-Smads) play important roles to negatively regulate TGF-β/BMP (bone morphogenetic protein) signaling, thus controlling numerous cellular and developmental processes. Recent studies have suggested that Smad7, a member of I-Smads, is overexpressed in numerous cancer types and its abundance is positively correlated to the malignancy. However, the molecular mechanism underlying action of I-Smads in cells remains poorly understood. Here we show that the Drosophila I-Smad, Dad, accesses the membrane via palmitoylation to target the BMP type I receptor for ubiquitination. Importantly, we show that the palmitoyltransferase dHIP14 catalyzes Dad palmitoylation and antagonizes BMP/Dpp signaling. Our findings uncover a mechanism by which I-Smad controls TGF-β/BMP signaling.

The intestine, a high-turnover tissue, plays a critical role in regulating aging and health in both vertebrates and invertebrates. Maintaining the epithelial barrier function of the intestine by preserving innate immune homeostasis significantly delays aging and prevents mortality. In an effort to explore effective chemicals and materials that can improve intestinal integrity, we performed a nonbiased screen utilizing Drosophila as an animal model. We showed that long-term uptake of aspirin markedly prevented age-onset gut leakage, the over-proliferation of intestinal stem cells, and the dysbiosis of commensal microbiota in fruit flies. Mechanistically, aspirin efficiently downregulated chronic activation of intestinal immune deficiency signaling during aging. Furthermore, our in vivo and in vitro biochemical analyses indicated that aspirin is a negative modulator in control of the K63-linked ubiquitination of Imd. Our findings uncover a novel regulatory mechanism by which aspirin positively modulates intestinal homeostasis, thus delaying aging, in Drosophila.