Hyd ubiquitinates the NF-κB co-factor Akirin to operate an effective immune response in Drosophila

Abstract

The Immune Deficiency (IMD) pathway in Drosophila melanogaster is activated upon microbial challenge with Gram-negative bacteria to trigger the innate immune response. In order to decipher this nuclear factor κB (NF-κB) signaling pathway, we undertook an in vitro RNAi screen targeting E3 ubiquitin ligases specifically and identified the HECT-type E3 ubiquitin ligase Hyperplastic discs (Hyd) as a new actor in the IMD pathway. Hyd mediated Lys 63 (K63)-linked polyubiquitination of the NF-κB cofactor Akirin was required for efficient binding of Akirin to the NF-κB transcription factor Relish. We showed that this Hyd-dependent interaction was required for the transcription of immunity-related genes that are activated by both Relish and Akirin but was dispensable for the transcription of genes that depend solely on Relish. Therefore Hyd is key in NF-κB transcriptional selectivity downstream of the IMD pathway. Drosophila depleted of Akirin or Hyd failed to express the full set of genes encoding immune-induced anti-microbial peptides and succumbed to immune challenges. We showed further that UBR5, the mammalian homolog of Hyd, was also required downstream of the NF-κB pathway for the activation of Interleukin 6 (IL6) transcription by LPS or IL-1β in cultured human cells. Our findings link the action of an E3 ubiquitin ligase to the activation of immune effector genes, deepening our understanding of the involvement of ubiquitination in inflammation and identifying a potential target for the control of inflammatory diseases.

The UBR box E3 ligases Poe and Hyd are required for efficient Pericentrin degradation

“…Multiple regions of the protein appear to contain sequences that regulate its degradation and multiple ubiquitin ligase components appear to be involved. Moreover, our screen identified Rad6 (E2) (Dohmen, 1991), UbcD1 (E2) (Treier, 1992), Poe (E3) (Ashton-Beaucage, 2016;Kim, 2018) and Hyd (E3) (Cammarata-Mouchtouris, 2020;Dorogova, 2020;Kinsella, 2016) as regulators of PLP . Poe (E3) (human UBR4) and Hyd (E3) (human UBR5) are N-recognins, members of a family of UBR box containing E3 ligases known to recognize the substrates of N-end rule ubiquitination system (Kim, 2018;Tasaki, 2009).…”

“…Interestingly, Rad6 (E2) is known to function with Poe (E3) in its N-end rule regulation of proteins involved in vesicular trafficking and the lysosomal pathway (Hong, 2015). Hyd (E3) has been studied in context of the N-end rule in regulating Hedgehog signaling, oogenesis, and immune response in Drosophila (Cammarata-Mouchtouris, 2020;Dorogova, 2020;Moncrieff, 2015), while its human ortholog UBR5 was studied in ovarian cancer signaling, tissue homeostasis, and miRNA mediated translational control (Cho, 2017;Hughes, 2021;Mellis, 2021;Tasaki, 2012). Finally, while UbcD1 (E2) has not been linked to the N-end rule, it does show high similarity to UBC4 (Treier, 1992), which is an E2 known to function with 13 Hyd (E3) /UBR5 in yeast (Stoll, 2011).…”

Metarhizium anisopliae is a valuable grist for biocontrol in beta‐cypermethrin‐resistant Blattella germanica (L.)

“…These data have allowed for the reconstruction of significant aspects of the host's immune pathways and the nature of the response to M. anisopliae . For example, the Akirin gene plays a primary role in immune defense in the epidermis of insects following natural fungal infection, linking the transcription factor NFκB in the IMD pathway 73,74 …”

Verloren negatively regulates the expression of IMD pathway dependent antimicrobial peptides in Drosophila

“…Taken together, our data indicated that Velo is a new negative regulator of the IMD pathway both in vitro and in vivo systems. We suspect that due to some technical limitations, we cannot address some critical questions yet, like what are the targets of Velos in the nucleus and/or the cytoplasm, what if nuclear Velo affects chromatin remodeling or probably modulates Akirin-mediated NF-κB signaling 58 , 70 , 75 , 76 , how Velo contributes to SUMOylation status of the IMD pathway, etc. Further analyses will be required to understand the Velo-mediated negative regulation mechanism in the IMD pathway.…”