Function and mechanism of the gasdermin family

Abstract

Inflammasomes are signaling structures of the innate immune system that activate caspase-1 and other inflammatory caspases (caspase-4 and -5 in humans and -11 in mice) in response to pathological challenges and endogenous, sterile damage. Inflammatory caspases cleave gasdermin (GSDM) D (GSDMD) in the cytosol of innate immune cells to release the functional, pore-forming N-terminal fragment (NT) of GSDMD from its auto-inhibitory C-terminal fragment (CT). GSDMD-NT translocates to the plasma membrane and possibly other types of membranes and then oligomerizes to form transmembrane pores. GSDMD pores regulate the release of alarmins including interleukin (IL)-1 family cytokines, including IL-1β and IL-18, from living cells and can also drive pyroptosis, a highly inflammatory form of programmed cell death that features cell swelling, membrane lysis, and leakage of cytosolic contents. In other cellular contexts, GSDMD can be proteolytically activated by enzymes beyond inflammatory caspases, including caspase-8, neutrophil elastase, and cathepsin G. The released alarmins serve to recruit immune cells to the site of perceived infection or damage. GSDMD is the prototypical member of the GSDM family, which in addition to GSDMD comprises five other GSDMs in humans (GSDMA, GSDMB, GSDMC, GSDME also known as (aka.) DFNA5, and GSDMF aka. PJVK aka. DFNB59) and nine in mice (GSDMA1-3, GSDMC1-4, GSDME, GSDMF). All these mammalian GSDMs except for GSDMF feature the NT-CT two-domain auto-inhibited architecture. They are cleaved by a variety of enzymes downstream of different activation pathways to mediate pore formation, cell death, and cytokine release in many cell types. Consistent with their diverse biological functions, GSDMs are associated with a multitude of diseases including inflammatory disorders and cancer and represent promising therapeutic targets. Through a combination of structural biology, biochemistry, and cell biology experiments, we (the GSDM team whose composition is detailed in the first sections of Chapters 2-6) discovered key mechanisms of proteolytic activation, membrane association, oligomerization, and insertion of the GSDM family. These insights led us to a mechanistic model of IL-1 release through the GSDMD pore. We also identified a GSDMD-targeting therapeutic and a critical role of GSDME in anti-tumor immunity. In this dissertation, we will provide readers with an up-to-date review on GSDMs, summarize our experimental findings, and discuss the prospects and therapeutic values of GSDM research.