Characterization of GSDME in amphioxus provides insights into the functional evolution of GSDM-mediated pyroptosis

Abstract

Members of the gasdermin (GSDM) family are pore-forming effectors that cause membrane permeabilization and pyroptosis, a lytic proinflammatory type of cell death. To reveal the functional evolution of GSDM-mediated pyroptosis at the transition from invertebrates to vertebrates, we conducted functional characterization of amphioxus GSDME (BbGSDME) and found that it can be cleaved by distinct caspase homologs, yielding the N253 and N304 termini with distinct functions. The N253 fragment binds to cell membrane, triggers pyroptosis, and inhibits bacterial growth, while the N304 performs negative regulation of N253-mediated cell death. Moreover, BbGSDME is associated with bacteria-induced tissue necrosis and transcriptionally regulated by BbIRF1/8 in amphioxus. Interestingly, several amino acids that are evolutionarily conserved were found to be important for the function of both BbGSDME and HsGSDME, shedding new lights on the functional regulation of GSDM-mediated inflammation.

An ancient defense mechanism: Conservation of gasdermin-mediated pyroptosis

“…Previous studies on gasdermins mostly focused on their functional roles in the immune response, and their origin and evolution have not been well studied. In this issue of PLOS Biology , Wang and colleagues investigated the evolutionary history of GSDM genes across metazoan species using bioinformatic methods [ 8 ]. Consistent with another recent study [ 9 ], Wang and colleagues found that GSDME is the most ancient GSDM gene and that the evolution of gasdermins can be divided into 2 clades: the gasdermin A/B/C/D clade, which is specific to jawed vertebrates, and the gasdermin E/pejvakin clade, which is widely distributed from cnidaria to mammals [ 8 ].…”

“…In this issue of PLOS Biology , Wang and colleagues investigated the evolutionary history of GSDM genes across metazoan species using bioinformatic methods [ 8 ]. Consistent with another recent study [ 9 ], Wang and colleagues found that GSDME is the most ancient GSDM gene and that the evolution of gasdermins can be divided into 2 clades: the gasdermin A/B/C/D clade, which is specific to jawed vertebrates, and the gasdermin E/pejvakin clade, which is widely distributed from cnidaria to mammals [ 8 ]. Within the gasdermin E/pejvakin clade, PJVK was a duplication from GSDME but lost the last 3 exons that encode the C-terminal autoinhibitory domain in early vertebrates.…”

“…In their study, Wang and colleagues focused on the invertebrate amphioxus and found that amphioxus gasdermin E ( Bb GSDME) induced significant pyroptosis in HeLa cells stimulated with TNFα and cycloheximide for the activation of caspase-3, and identified 3 caspase homologs ( Bb CASP1/2/3-like) as the upstream enzymes of Bb GSDME [ 8 ]. Interestingly, Bb GSDME contains 2 caspase cleavage sites (at D253 and D304) responsible for generating a p30 or a p40 N-terminal fragment of Bb GSDME, respectively, upon cleavage by caspases.…”

“…Wang and colleagues then generated an atomic model of Bb GSDME in the pore conformation based on the structure of human gasdermin D [ 8 ]. The simulated model, combined with their biochemical studies, revealed highly conserved lipid-binding and oligomerization interfaces in Bb GSDME.…”

“…Overall, the new study provides insights into the origin and evolution of the gasdermin family across metazoans [ 8 ]. The functional analysis of Bb GSDME in amphioxus highlighted its ancient role in innate immune response and revealed a novel negative feedback regulation of gasdermin-mediated pyroptosis.…”