Le Guerroue, F. | Search bioRxiv

bioRxiv2023

STING induces LUBAC-mediated synthesis of linear ubiquitin chains to stimulate innate immune signaling

STING activation by cyclic dinucleotides in mammals induces IRF3- and NF{kappa}B -mediated gene expression, and the lipidation of LC3B at Golgi-related membranes. While mechanisms of the IRF3 response are well understood, the mechanisms of NF{kappa}B activation mediated by STING remain unclear. We report that STING activation induces linear/M1-linked ubiquitin chain (M1-Ub) formation and recruitment of the LUBAC E3 ligase, HOIP, to LC3B-associated Golgi membranes where ubiquitin is also localized. Loss of HOIP prevents formation of M1-Ub ubiquitin chains and reduces STING-induced NF{kappa}B and IRF3-mediated signaling in human monocytic THP1 cells and mouse bone marrow derived macrophages, without affecting STING activation. STING-induced LC3B lipidation is not required for M1-Ub chain formation or the immune-related gene expression, however the recently reported function of STING to neutralize the pH of the Golgi may be involved. Thus, LUBAC synthesis of M1 ubiquitin chains mediates STING-induced innate immune signaling.

cell biology↗

bioRxiv2022

TNIP1 inhibits Mitophagy via interaction with FIP200 and TAX1BP1

Mitophagy is a form of selective autophagy that disposes of superfluous and potentially damage-inducing organelles in a tightly controlled manner. While the machinery involved in mitophagy induction is well known, the regulation of the components is less clear. For example, it is still unknown how the ULK1 complex is dissociated prior to closing of the autophagosome. Here, using Chemically Inducible Dimerization (CID) and mitophagy assays with the fluorescent probe mtKeima, we reveal that the ubiquitin binding domain-containing protein TNIP1 is able to induce mitophagy when ectopically targeted to mitochondria. Conversely, we demonstrate that TNIP1 knock down accelerates mitophagy rates, and that ectopic TNIP1 negatively regulates the rate of mitophagy. These functions of TNIP1 depend on a previously unrecognized, evolutionarily conserved LIR motif as well as its AHD3 domain, which are required for binding to the ULK1 complex member FIP200 and the autophagy receptor TAX1BP1, respectively. Taken together, our findings identify a novel negative regulator of mitophagy that acts at the early steps of autophagosome biogenesis and provide a molecular rationale for how the ULK1 complex might be dissociated from the closing autophagosome.

cell biology↗