Abstract
ABSTRACT
Mycobacterial infection induces dynamic transcriptional changes in both the host and pathogen. In slow-growing mycobacteria, the ESX-5 secretion system plays a crucial role in virulence by exporting Pro–Glu (PE) and Pro–Pro–Glu (PPE) proteins, which modulate host immune responses and contribute to pathogenesis. Previous studies demonstrated that
ppe27
overexpression in
Mycobacterium smegmatis
enhances bacterial survival and promotes host cell death, suggesting that PPE27 plays an important role in resistance to macrophage-induced cytotoxicity. However, its function during host–pathogen interactions remains poorly defined. To elucidate the function of PPE27, we generated a
ppe27
deletion mutant of
Mycobacterium bovis
Bacillus Calmette–Guérin (BCG∆
ppe27
) and performed RNA-seq to simultaneously profile host and bacterial transcriptional responses during macrophage infection. Host transcriptome analysis revealed that
ppe27
deletion led to upregulated pro-inflammatory responses, including enhancement of the TNF-α, IFN-α, and IL-6 signaling pathways. In parallel, bacterial transcriptome analysis identified downregulation of
JTY_3006
in BCG∆
ppe27
during infection compared with its expression in wild-type BCG. Amino acid sequence analysis indicated that
JTY_3006
shares 100% identity to a S-adenosylmethionine (SAM)-dependent methyltransferase conserved among mycobacterial species. Taken together, these findings suggest that PPE27 may contribute to the negative modulation of host inflammatory responses and suggest that manipulation of PPE27 might reshape pathogenicity and inform future vaccine strategies.
IMPORTANCE
Tuberculosis remains the leading cause of death from a single infectious agent worldwide. Understanding the mechanisms that allow
Mycobacterium tuberculosis
to evade host defenses is essential for developing better vaccines, therapeutics, and prevention strategies. This study focuses on PPE27, a member of the PE/PPE protein family secreted through the ESX-5 secretion system. Although PE/PPE proteins are known to trigger strong immune responses, their precise role in pathogenesis has been unclear. Our study reveals that
ppe27
deletion is associated with enhanced macrophage inflammatory responses. Understanding this mechanism provides valuable insight into host–pathogen interactions and offers new directions for tuberculosis vaccine and therapeutic development.