Mycobacterium tuberculosis Serine Protease Rv3668c Can Manipulate the Host-Pathogen Interaction via Erk-NF-κB Axis-Mediated Cytokine Differential Expression

Tuberculosis caused by Mycobacterium tuberculosis (MTB) remains a serious global public health concern. About one-third of the global population has been latently infected with this pathogen. MTB proteases are important virulence factors and involve in subverting the host immunity. MTB protease Rv3668c was implicated in drug action and dormancy by Gene Expression Omnibus data. To define the role of Rv3668c in pathogen-host interaction, we constructed recombinant strain Mycobacterium smegmatis-Rv3668c (Ms-Rv3668c). The resultant strains were used to challenge the human macrophage cell line U937. The cytokine levels and the survival of recombinants and macrophages were monitored. The results showed that recombinant Ms-Rv3668c specifically upregulated the secretion of proinflammatory cytokines TNF-alpha, IL-1 beta, and IL-6 and downregulated the secretion of anti-inflammatory cytokine IL-10 by U937 cells, consistent with the upregulated transcription of TNF-alpha and IL-1 beta. Rv3668c recombinants demonstrated prolonged survival within the U937 cells and accelerated the death of the host cells. Inhibitor experiments showed that the ERK-NF-kappa B axis was involved in the Rv3668c-triggered TNF-alpha and IL-1 beta changes. These results provided evidence for the engagement of Rv3668c in the interaction between Mycobacterium and host.