Host Pore-Forming Protein Complex Neutralizes the Acidification of Endocytic Organelles to Counteract Intracellular Pathogens

Abstract

Many intracellular pathogens invade cells via endocytic organelles and have adapted to the drop in pH along the endocytic pathway. However, the strategy by which the host cell counteracts this pathogen adaptation remains unclear. βγ-CAT is an aerolysin-like pore-forming protein and trefoil factor complex in the frog Bombina maxima. We report here that βγ-CAT, as a host-secreted factor with an intrinsic channel-forming property, is the first example of a molecule that actively neutralizes the acidification of endocytic organelles to counteract Listeria monocytogenes infection. Immunodepletion of endogenous βγ-CAT largely impaired the control of L. monocytogenes by frog cells. βγ-CAT elevates the pH of L. monocytogenes-containing vacuoles to limit the vacuole escape of L. monocytogenes to cytosol. Furthermore, βγ-CAT promotes intracellular L. monocytogenes clearance via autophagy and by that the nonlytic expulsion of the bacteria from host cells. Finally, βγ-CAT attenuated the dissemination of L. monocytogenes in vivo. These findings reveal a novel host strategy and effectors that combat pathogen adaptation to acidic conditions along the endocytic pathway.

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 .…”

A secreted pore‐forming protein modulates cellular endolysosomes to augment antigen presentation

“…24 Previous studies have illustrated its roles in frog innate immunity and tissue repair. [24][25][26][27] βγ-CAT exerts its cellular effects by targeting the acidic glycosphingolipids in lipid rafts of the cell plasma membrane via a double-receptor binding model to initiate the endocytosis of its α-subunit BmALP1, 28 and the subsequent oligomerization and pore formation of BmALP1 on cellular endolysosomes through endocytic pathways, 24,27 which is negatively regulated by paralog of βγ-CAT in a redox-dependent manner. 29 This process modulates the content and biochemical properties of these intracellular vesicles, leading to various cellular responses and outcomes depending on different cell contexts.…”

“…29 This process modulates the content and biochemical properties of these intracellular vesicles, leading to various cellular responses and outcomes depending on different cell contexts. 26,27 βγ-CAT is able to activate inflammasomes to initiate effective innate antimicrobial responses. 26 In addition, it neutralizes endocytic organelle acidification to counteract intracellular pathogen invasion.…”

“…26 In addition, it neutralizes endocytic organelle acidification to counteract intracellular pathogen invasion. 27 Though the effect of this vertebrate PFP βγ-CAT on host innate immunity has been uncovered, whether βγ-CAT directly affects the adaptive immune response is unknown. Here, we intended to investigate the effects of βγ-CAT on DCs and subsequent adaptive immune responses.…”

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

“…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). To date, we know of no research on the function of bg-CAT in wound healing.…”