Interleukin-1β Maturation Triggers Its Relocation to the Plasma Membrane for Gasdermin-D-Dependent and -Independent Secretion

TLDR

IL‑1β must be cleaved by caspase‑1 to become active, and its secretion from inflammasome‑activated macrophages depends on caspase‑1‑mediated GSDMD cleavage, but how IL‑1β is released by pyroptotic versus non‑pyroptotic cells remains unclear. We demonstrate that IL‑1β maturation drives its trafficking to PIP2‑rich plasma membrane ruffles via a polybasic motif, enabling both GSDMD‑dependent rapid release and a slower, GSDMD‑independent secretion that persists in non‑pyroptotic cells.

Abstract

IL-1β requires processing by caspase-1 to generate the active, pro-inflammatory cytokine. Acute IL-1β secretion from inflammasome-activated macrophages requires caspase-1-dependent GSDMD cleavage, which also induces pyroptosis. Mechanisms of IL-1β secretion by pyroptotic and non-pyroptotic cells, and the precise functions of caspase-1 and GSDMD therein, are unresolved. Here, we show that, while efficient early secretion of endogenous IL-1β from primary non-pyroptotic myeloid cells in vitro requires GSDMD, later IL-1β release in vitro and in vivo proceeds independently of GSDMD. IL-1β maturation is sufficient for slow, caspase-1/GSDMD-independent secretion of ectopic IL-1β from resting, non-pyroptotic macrophages, but the speed of IL-1β release is boosted by inflammasome activation, via caspase-1 and GSDMD. IL-1β cleavage induces IL-1β enrichment at PIP2-enriched plasma membrane ruffles, and this is a prerequisite for IL-1β secretion and is mediated by a polybasic motif within the cytokine. We thus reveal a mechanism in which maturation-induced IL-1β trafficking facilitates its unconventional secretion.