Host-derived, pore-forming toxin–like protein and trefoil factor complex protects the host against microbial infection

Abstract

Aerolysins are virulence factors belonging to the bacterial β-poreforming toxin superfamily. Surprisingly, numerous aerolysin-like proteins exist in vertebrates, but their biological functions are unknown. βγ-CAT, a complex of an aerolysin-like protein subunit (two βγ-crystallin domains followed by an aerolysin pore-forming domain) and two trefoil factor subunits, has been identified in frogs (Bombina maxima) skin secretions. Here, we report the rich expression of this protein, in the frog blood and immune-related tissues, and the induction of its presence in peritoneal lavage by bacterial challenge. This phenomena raises the possibility of its involvement in antimicrobial infection. When βγ-CAT was administrated in a peritoneal infection model, it greatly accelerated bacterial clearance and increased the survival rate of both frogs and mice. Meanwhile, accelerated Interleukin-1β release and enhanced local leukocyte recruitments were determined, which may partially explain the robust and effective antimicrobial responses observed. The release of interleukin-1β was potently triggered by βγ-CAT from the frog peritoneal cells and murine macrophages in vitro. βγ-CAT was rapidly endocytosed and translocated to lysosomes, where it formed high molecular mass SDS-stable oligomers (>170 kDa). Lysosomal destabilization and cathepsin B release were detected, which may explain the activation of caspase-1 inflammasome and subsequent interleukin-1β maturation and release. To our knowledge, these results provide the first functional evidence of the ability of a host-derived aerolysin-like protein to counter microbial infection by eliciting rapid and effective host innate immune responses. The findings will also largely help to elucidate the possible involvement and action mechanisms of aerolysin-like proteins and/or trefoil factors widely existing in vertebrates in the host defense against pathogens.innate immunity | infectious disease | interleukin-1beta

Overexpression of Porcine Beta-Defensin 2 Enhances Resistance to Actinobacillus pleuropneumoniae Infection in Pigs

“…1B). Culture supernatant of the pcCAG-PBD2-transfected cells showed obvious antibacterial effects by disk zone inhibition assay, whereas the cell lysates displayed the same killing activities against A. pleuropneumoniae as the mock-treated con-cell types (18). The TG founders then were crossed with WT Large White sows to generate TG pigs (F1).…”

Lysosomal membrane permeabilization and cell death

“…Molecules that induce pore formation in membranes can also induce LDCD . Examples include certain bacterial agents as well as endogenous toxin‐like molecules, such as aerolysins, which induce cell death and thus counteract bacterial infection by attenuating the acidification of endocytic organelles . Studies have demonstrated that the translocation of Bax and Bak to lysosomal membranes result in LMP and cell death .…”

Pore‐forming toxin‐like protein complex expressed by frog promotes tissue repair

“…A bg-crystallin fused aerolysin-like protein (a-subunit) and trefoil factor (b-subunit) complex (bg-CAT) was previously isolated and purified from the skin secretions of Bombina maxima. The a-subunit of bg-CAT is a bg-crystallin-fused ALP (15). The b-subunit of bg-CAT is a 3-domain trefoil factor (19), which is widely distributed in the gastrointestinal tract and is present in virtually all mucous membranes in mammals (20).…”

“…Unlike several pore-forming toxins that are produced by pathogenic bacteria that can directly oligomerize and form pores in host-cell membranes for invasion (10,11), the most characteristic biologic pathway of bg-CAT is targeting endocytic organelles after endocytosis to regulate intracellular vesicles (15,19,21). bg-CAT is endocytosed and modulated lysosomal stabilization, then Caspase-1 is activated through the inflammasome and leads to the recruitment of innate immune cells that will eventually clear the extracellular bacteria (15). This protein complex also actively neutralizes the acidification of endocytic organelles to counteract intracellular bacterial infection (21).…”