TRIMming down Mycobacterium tuberculosis replication: TRIM32 is required for bacterial ubiquitination and autophagy induction in macrophages

Mycobacterium tuberculosis (Mtb) promotes its intracellular persistence by subverting defense mechanisms, such as autophagy. Remarkably, enhancing autophagy is sufficient to trigger intracellular Mtb killing and effective immune response, making this process a valid target of host-directed therapies. However, several aspects of autophagy regulation during Mtb infection remain unsolved. Tripartite motif (TRIM) proteins are a large family of ubiquitin ligases primarily involved in innate immunity by regulating inflammation and autophagy. By combining transcriptomic and infectivity screens, we recently identified a set of TRIMs that modulate Mtb replication. In detail, overexpression of TRIM22 and TRIM32 reduces Mtb growth in THP1 macrophages, while that of TRIM36 and TRIM56 promotes Mtb replication. Analysis of the molecular mechanisms underlying inhibition of Mtb replication by TRIM32 showed that its overexpression promote xenophagy, a selective autophagy of pathogens, by increasing Mtb ubiquitination and the recruitment of CALCOCO2/NDP52 (calcium binding and coiled-coil domain 2) and MAP1LC3B (microtubule-associated protein 1 light chain 3B) to intracellular bacteria. Consistently, TRIM32 downregulation reduces the xenophagic response, resulting in increased Mtb replication. Altogether, we characterized a novel role for TRIM32 in the host response to pathogen infections and identify TRIM36 and TRIM56 as possible host factors required for Mtb infection.