Drosophila Cul3 contributes to Diap2-mediated innate immune signaling for antimicrobial defense

The host antimicrobial immune response relies on a complex interplay of molecular mechanisms to effectively combat microbial infections. Herein, we investigate the functional role of Cullin-3 (Cul3), one critical constituent of cullin-RING ubiquitin ligases, in the Drosophila melanogaster (fruit fly) antimicrobial immune defense. We show that silencing of Cul3 leads to a decreased induction of antimicrobial peptides and high mortality in adult flies after bacterial infection. Through biochemical approaches, we demonstrate that Cul3 predominantly relies on its BTB-binding domain (BD) and neddylation domain (ND) to physically associate with death-associated inhibitor of apoptosis 2 (Diap2). Importantly, Cul3 ameliorates the Diap2-mediated ubiquitination of death-related ced-3/Nedd2-like caspase (Dredd), a process essential for robust immune deficiency (IMD) signaling upon bacterial infection. Taken together, our findings highlight a previously unrecognized regulatory axis of Cul3/Diap2/Dredd in the fly antimicrobial immune defense, providing potential insights into therapeutic strategies for combating bacterial infections in humans. • Cul3 plays an essential role in the Drosophila antimicrobial innate immune defense • Cul3 directly interacts with Diap2 in a domain-dependent manner • Cul3 regulates the Diap2-mediated ubiquitination of Dredd