The phosphate exporter XPR1 promotes gasdermin D-independent mature IL-1β secretion

Interleukin (IL)-1β is a leaderless inflammatory cytokine that is not secreted via the classical endoplasmic reticulum-Golgi pathway. Instead, m(ature) IL-1β secretion is classically associated with pyroptosis, a caspase-dependent inflammatory cell death mediated by gasdermin D (GSDMD) pore formation at the plasma membrane. However, human monocytes can secrete mIL-1β in the absence of cell death, and the contribution of GSDMD in this secretory pathway remains poorly defined. Here, we distinguished two pathways for mIL-1β secretion in living human monocytic cells : a rapid, GSDMD-dependent pathway and a slower, GSDMD-independent pathway. Using a genome-wide CRISPR-Cas9 screen, we identified XPR1 (Xenotropic and Polytropic retrovirus Receptor 1) as a regulator of the GSDMD-independent pathway. XPR1, the only phosphate exporter identified in metazoans, has not previously been implicated in cytokine secretion. Genetic invalidation of XPR1 in GSDMD-deficient monocytic cells markedly reduced IL-1β secretion. We further showed that this regulatory function requires XPR1 surface expression and phosphate export activity. These findings reveal an unexpected link between phosphate homeostasis and non-lytic mIL-1β secretion, opening new opportunities to modulate IL-1β-driven inflammatory diseases.