Cytotoxic Cells Kill Intracellular Bacteria through Granulysin-Mediated Delivery of Granzymes

Abstract

Summary When killer lymphocytes recognize infected cells, perforin delivers cytotoxic proteases (granzymes) into the target cell to trigger apoptosis. What happens to intracellular bacteria during this process is unclear. Human, but not rodent, cytotoxic granules also contain granulysin, an antimicrobial peptide. Here we show that granulysin delivers granzymes into bacteria to kill diverse bacterial strains. In E. coli, granzymes cleave electron transport chain complex I and oxidative stress defense proteins, generating ROS that rapidly kill bacteria. ROS scavengers and bacterial antioxidant protein overexpression inhibit bacterial death. Bacteria overexpressing a GzmB-uncleavable mutant of the complex I subunit nuoF or strains that lack complex I still die, but more slowly, suggesting that granzymes disrupt multiple vital bacterial pathways. Mice expressing transgenic granulysin are better able to clear L. monocytogenes. Thus killer cells play an unexpected role in bacterial defense.

Amplifying renal immunity: the role of antimicrobial peptides in pyelonephritis

“…Net cationic charge, as indicated by a high isoelectric point (pI), permits AMPs to bind negatively charged microbial cell surface components. 48,49 Amphipathicity, which refers to the tendency of an AMP to remain in solution in both hydrophilic and hydrophobic environments, is a key requisite for AMPs to disrupt lipid bilayers. Secondary structure motifs such as α-helices and β-sheets stabilize AMP pore formation in microbial lipid bilayers, whereas disulphide bridges between cysteine residues maintain AMP structural integrity.…”

“…56 In addition, AMPs interact with host cells to modulate antimicrobial responses and activate host innate and adaptive immune effector cells ( Figure 5). 48,49 The following sections describe the published literature on the function(s) and cellular sources of urinary tract AMPs and other innate immune proteins.…”

Granzyme B Disrupts Central Metabolism and Protein Synthesis in Bacteria to Promote an Immune Cell Death Program

“…The cytotoxic granule pore-forming protein, perforin (PFN), delivers the death-inducing granzyme (Gzm) serine proteases into the target cell, where they cleave multiple substrates to kill the target cell. These cytotoxic cells also kill intracellular bacteria and protozoa (Dotiwala et al, 2016; Walch et al, 2014). Granulysin (GNLY), another pore-forming protein in the cytotoxic granules of killer cells of most mammals, but not rodents, selectively permeabilizes microbial membranes (Stenger et al, 1998) and delivers the Gzms into intracellular microbes to cause rapid microbial death before the host cell is killed.…”

Inhalation of recombinant adenovirus expressing granulysin protects mice infected with Mycobacterium tuberculosis

“…4 Granulysin is also able to generate pores on the surface of bacteria, promoting infiltration of the granzymes into the bacterial cytosol and killing various bacteria via the generation of radical oxygen species (ROS). 7 In particular, synthetic peptides based on granulysin also exhibit better inhibition activity to single drug-resistant and even MDR-TB strains in vitro, 8 and in transgenic mice that constitutively express human granulysin, there is significantly inhibition of the growth of M. tuberculosis in infected mice. 9 However, to kill intracellular M. tuberculosis, granulysin depends on the effect of perforin to cross the cell membrane of host cells.…”