TRIM21 blocks DDX3X-driven stress granule formation during Mycobacterium tuberculosis infection via a non-canonical E3 ligase mechanism.

Tripartite motif-containing 21 (TRIM21) is an E3 ubiquitin ligase that binds viral and host proteins to mediate antiviral defense. Its role in Mycobacterium tuberculosis (Mtb) infection, however, is unclear. Here, our analysis of human TB transcriptomic datasets showed that TRIM21 expression levels correlate with TB progression in human patients. We further demonstrated that TRIM21 deficiency suppresses Mtb growth in both macrophages and a murine model of tuberculosis (TB). Mechanistically, TRIM21 limits host resistance to Mtb through a non-canonical pathway distinct with its E3 ligase activity. It physically interacts with the RNA helicase DEAD-box helicase family member DDX3X and disrupts phase separation dynamics required for stress granule (SG) assembly. Impaired SG formation compromises innate immune responses, thereby facilitating intracellular bacterial growth and creating a permissive cellular environment for Mtb growth. Consistent with these genetic findings, pharmacological inhibition of TRIM21 restricted Mtb growth in experimental macrophage and murine models. Together, these findings uncover a non-canonical role of TRIM21 in Mtb infection and highlight its potential as a therapeutic target for host-directed therapy against TB.