ABSTRACT The mycobacterial ESX-1 (Type VII) secretion system is essential for virulence and induces the NLRP3 inflammasome activation. However, the specific bacterial effectors involved in this process, beyond the well-characterized EsxA (ESAT-6), remain largely unidentified. Through systematic screening of ESX-1 effectors, we identified EspF as a potent and evolutionarily conserved activator of the NLRP3 inflammasome across pathogenic mycobacterial species, including Mycobacterium tuberculosis, M. bovis, and M. marinum. Our results demonstrate that EspF significantly augments the mature IL-1β and IL-18 release, ASC speck formation, caspase-1 activation, and gasdermin D (GSDMD)-mediated pyroptosis in THP-1 cells. Notably, infection with M. smegmatis or M. bovis BCG strain overexpressing EspF significantly enhanced NLRP3 inflammasome activation and pyroptosis, which were completely abolished in NLRP3-deficient cells. Mechanistically, EspF directly interacts with the NACHT and LRR domains of NLRP3. Furthermore, unbiased proteomic screening identified the host E3 ubiquitin ligase TRIM25 as an indispensable binding partner. In THP-1 cells, we confirmed the endogenous interaction and colocalization of the EspF–TRIM25–NLRP3 complex, demonstrating that EspF functions as a molecular scaffold that bridges TRIM25 to NLRP3. This proximity interaction, further validated in situ during mycobacterial infection, facilitates TRIM25-mediated K63-linked ubiquitination of NLRP3. In vivo, mice infected with M. bovis BCG strains overexpressing EspF exhibited exacerbated lung lesions, increased inflammatory cell infiltration, and higher bacterial burdens. Collectively, these findings reveal EspF-TRIM25-NLRP3 axis is a novel mechanism of mycobacterial pathogenesis that drives hyperinflammation to facilitate bacterial survival and dissemination.
Yang Yang, Yi-Xin Han, Long-Jian Wu et al.· Virulence· 0 citations
ABSTRACT The high genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) poses a significant challenge to effective vaccination and infection prevention. Recently, NADC30-like PRRSV has become dominant in China. In this study, we characterized a PRRSV isolate XJ2020 from a vaccinated pig. The isolate exhibited moderate pathogenicity in piglets and clustered within the same sub-lineage as NADC30. Sequence analysis identified a unique deletion of the serine residue at position 32 (S32) in the GP5 protein. This deletion was introduced into a highly pathogenic PRRSV (HP-PRRSV) strain, JX2015, to generate the mutant JX2015-ΔS32 using a reverse genetic approach. We found that JX2015-△S32 showed reduced propagation in Marc-145 cells and decreased sensitivity to neutralization by MLV-derived anti-PRRSV positive serum, but exhibited enhance replication in primary porcine alveolar macrophages (PAMs) compared to its parental strain JX2015. Interestingly, the viral load in lung and ileum samples from JX2015-△S32-infected piglets was higher, but the lung injury was milder than in JX2015-infected piglets. Overall, this study highlights the S32 site in the PRRSV GP5 protein as an important factor influencing virus propagation, neutralization, cell tropism and pathogenicity in piglets, and suggests that targeting this residue could lead to the development of more effective PRRSV vaccines.
Xingdong Zhou, Xiao-Hui Zhang, E. Kan et al.· Virulence· 0 citations
Transcriptional analysis revealed that compared to neutral conditions, osmotic stress-related genes were significantly upregulated in the ΔliaS strain under acidic conditions, indicating that LiaS modulates acid tolerance through transcriptional regulation.
Yong-Shu Wu, Jiali Xu, Yifan Wang et al.· Virulence· 0 citations
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