The E3 ubiquitin ligase HECTD3 controls immune colonic inflammation by restricting Myd88 activation and signaling

Ubiquitination is an important post-translational modification associated with essential cellular processes and implicated in regulation of immunity. Here we show that deletion of the E3 ubiquitin ligase Hectd3, germline or in hematopoietic compartment, including in CD11c+ cells, causes a more severe DSS-induced colitis and increased production of proinflammatory cytokines. Hectd3 mRNA levels were found reduced in colonic tissues of patients with ulcerative colitis (UC), which highlights a potential role for Hectd3 in regulating inflammatory responses in UC. We identified Myd88, a central adaptor in the TLR/IL1R signaling and inflammatory response, as a target for Hectd3 ubiquitination. We demonstrate that Hectd3 directly ubiquitinates Myd88 through K27-linked Poly-Ub chains in a nondegradative manner. Hectd3 KO GM-CSF-bone marrow derived cells treated with the TLR4 ligand lipopolysaccharide (LPS) produced more proinflammatory cytokines, show elevated phosphorylation of NF-κB and IRAK4, as well as elevated association of Myd88 with IRAK4, demonstrating that Hectd3 controls Myd88-IRAK4-NF-κB axis. Inhibition of Myd88 activity rescued colitis severity in the Hectd3 KO mice, including the elevated proinflammatory cytokine production. Thus, our results establish Myd88 as a new target for Hectd3 non-degradative polyubiquitination and restriction of immune colonic inflammation.