The Drosophila Ubiquitin-Specific Protease dUSP36/Scny Targets IMD to Prevent Constitutive Immune Signaling

Abstract

Ubiquitin proteases remove ubiquitin monomers or polymers to modify the stability or activity of proteins and thereby serve as key regulators of signal transduction. Here, we describe the function of the Drosophila ubiquitin-specific protease 36 (dUSP36) in negative regulation of the immune deficiency (IMD) pathway controlled by the IMD protein. Overexpression of catalytically active dUSP36 ubiquitin protease suppresses fly immunity against Gram-negative pathogens. Conversely, silencing dUsp36 provokes IMD-dependent constitutive activation of IMD-downstream Jun kinase and NF-kappaB signaling pathways but not of the Toll pathway. This deregulation is lost in axenic flies, indicating that dUSP36 prevents constitutive immune signal activation by commensal bacteria. dUSP36 interacts with IMD and prevents K63-polyubiquitinated IMD accumulation while promoting IMD degradation in vivo. Blocking the proteasome in dUsp36-expressing S2 cells increases K48-polyubiquitinated IMD and prevents its degradation. Our findings identify dUSP36 as a repressor whose IMD deubiquitination activity prevents nonspecific activation of innate immune signaling.

The deubiquitinating enzyme USP36 controls selective autophagy activation by ubiquitinated proteins

“…Co-expression of the dUsp36-IR transgene and of an imd-IR transgene, which had been previously shown to efficiently inhibit imd gene expression, 23 did not significantly modify the level of autophagy induction (Fig. 3G) or the cell size reduction (Fig.…”

“…Our previous work identified dUSP36 as a negative regulator of the IMD pathway. 23 We showed that dUSP36 interacts with and deubiquitinates the IMD protein. dUsp36 silencing results in the constitutive activation of this NFkB dependent signaling pathway and consequently of the connected JNK pathway.…”

“…We previously reported that dUsp36 null mutants are lethal at larval stages. 23 To examine the cause of this lethality, larvae homozygous for a null dUsp36 mutation 23 were collected. Compared with wild-type larvae (Fig.…”

The Drosophila Imd Signaling Pathway

“…In addition, a number of ubiquitinating and deubiquitinating enzymes have been implicated in the negative regulation of the signaling pathway. The ubiquitin-specific protease dUSP36/Scny prevents the accumulation of the activated, K63-ubiquitinated Imd and promotes its K48-linked ubiquitination and subsequent degradation (72). faf is a deubiquitinating enzyme that also was proposed to regulate the ubiquitination state of Imd (73).…”

The multilayered innate immune defense of the gut

“…Additional negative regulators of the IMD pathway have been identified, mainly acting via ubiquitylation and the degradation of intracellular components of the cascade. [17,[95][96][97][98][99][100][101][102] Altogether, these regulatory components downregulate the IMD cascade following immune stimuli, allowing a balanced AMP response to be re-established once the infection is cleared. [103,104] Another layer of control is provided by the functional compartmentalization of the Drosophila gut.…”