Pore formation at the lytic synapse triggers the canonical pyroptotic cell death pathway

Prokaryotic pore-forming toxins drive inflammasome activation and pyroptosis through K+-dependent activation of the canonical NLRP3/caspase-1/gasdermin D signaling axis. In this study, we hypothesized that perforin, a eukaryotic pore-forming protein released into the lytic synapse by antigen-specific cytotoxic T lymphocytes (CTLs) upon cognate antigen recognition, mimics the pro-pyroptotic activity of ancestral pore-forming toxins, complementing its role as a conduit for granzymes. Utilizing imaging and molecular approaches, we demonstrate that perforation of target cells upon CTL attack elicits swift K+ efflux followed by NLRP3-dependent activation of proinflammatory caspase-1 and its major substrate, the pyroptotic executioner gasdermin D (GSDMD). Acute target cell death upon CTL attack is gasdermin-dependent and demonstrates morphological and molecular features of pyroptosis, including pyroptotic body formation, cell bloating, plasma membrane rupture, and release of intracellular contents. Perforation of target cells by soluble perforin is sufficient to trigger rapid K+ efflux, caspase-1 activation, and pyroptosis. By contrast, sustained interaction with CTLs unmasks a delayed apoptotic phenotype in the remaining target cells. Interestingly, exposure of target cells to exogenous supramolecular attack particles (SMAPs) recapitulates this apoptotic phenotype, suggesting that soluble perforin and SMAPs play dichotomous roles in target cell death. Our results reveal a novel mechanism for engagement of pyroptotic machinery upon CTL attack, in which perforin itself can autonomously engage programmed cell death (PCD), highlighting the complexity and diversity of the CTL lytic arsenal.