CXCL10 Acts as a Bifunctional Antimicrobial Molecule against Bacillus anthracis

Abstract

Bacillus anthracis is killed by the interferon-inducible, ELR(−) CXC chemokine CXCL10. Previous studies showed that disruption of the gene encoding FtsX, a conserved membrane component of the ATP-binding cassette transporter-like complex FtsE/X, resulted in resistance to CXCL10. FtsX exhibits some sequence similarity to the mammalian CXCL10 receptor, CXCR3, suggesting that the CXCL10 N-terminal region that interacts with CXCR3 may also interact with FtsX. A C-terminal truncated CXCL10 was tested to determine if the FtsX-dependent antimicrobial activity is associated with the CXCR3-interacting N terminus. The truncated CXCL10 exhibited antimicrobial activity against the B. anthracis parent strain but not the ΔftsX mutant, which supports a key role for the CXCL10 N terminus. Mutations in FtsE, the conserved ATP-binding protein of the FtsE/X complex, resulted in resistance to both CXCL10 and truncated CXCL10, indicating that both FtsX and FtsE are important. Higher concentrations of CXCL10 overcame the resistance of the ΔftsX mutant to CXCL10, suggesting an FtsX-independent killing mechanism, likely involving its C-terminal α-helix, which resembles a cationic antimicrobial peptide. Membrane depolarization studies revealed that CXCL10 disrupted membranes of the B. anthracis parent strain and the ΔftsX mutant, but only the parent strain underwent depolarization with truncated CXCL10. These findings suggest that CXCL10 is a bifunctional molecule that kills B. anthracis by two mechanisms. FtsE/X-dependent killing is mediated through an N-terminal portion of CXCL10 and is not reliant upon the C-terminal α-helix. The FtsE/X-independent mechanism involves membrane depolarization by CXCL10, likely because of its α-helix. These findings present a new paradigm for understanding mechanisms by which CXCL10 and related chemokines kill bacteria.

Bacillus anthracis Peptidoglycan Integrity Is Disrupted by the Chemokine CXCL10 through the FtsE/X Complex

“…Like Δ ftsX , the B. anthracis ftsE(K123A/D481N) mutant strain was also found to be less susceptible to CXCL10 and completely resistant to CTTC (Margulieux et al, 2016). Dual labeling of untreated B. anthracis ftsE(K123A/D481N) yielded similar results for EDA and TDL incorporation ( Figure 4A ) as observed with B. anthracis Δ ftsX ( Figure 3A ).…”

Mycobacterium tuberculosis-triggered Hippo pathway orchestrates CXCL1/2 expression to modulate host immune responses

“…However, amassing evidences suggest that they may also arm such immune cells with anti-microbial capacities to further enhance their efficacy to contain the immune insult5253. In this regard, it was intriguing to explore the capacity of mycobacteria-induced CXCL1 and CXCL2 in armoring neighboring macrophages with innate immune defenses like anti-microbial peptides (AMPs) such as beta-defensins (Defb) and inflammatory mediators including TNF-α, IL-1β, IL-12p40, iNOS (inducible nitric oxide synthase), NOX (NADPH oxidase) and LYZ (Lysozyme).…”

Transcriptional analysis defines TCR and cytokine-stimulated MAIT cells as rapid polyfunctional effector T cells that can coordinate the immune response

“…MAIT cells may also exercise direct killing of extracellular bacteria through the release of antibacterial peptides such as IL-26 (Meller et al, 2015) and antimicrobial chemokines such as CXCL9 and CXCL10 (Margulieux, Fox, Nakamoto, & Hughes, 2016; Reid-Yu, Tuinema, Small, Xing, & Coombes, 2015). This makes MAIT cells one of many cell populations contributing to the pool of antimicrobial peptides at the site of infection/inflammation.…”