Interleukin‐1β posttranslational processing—exploration of P2X 7 receptor involvement

Cultured monocytes and macrophages stimulated with LPS produce large quantities of prointerleukin (IL)‐1β, but release little mature cytokine to the medium. The efficiency at which the procytokine is converted to its active 17 kDa species and released extracellularly is enhanced by treating cytokine‐producing cells with a secretion stimulus such as ATP or nigericin. Alterations to the composition of the intracellular ionic environment, including a necessary K + efflux, accompany the stimulus‐induced secretory process. Cell death also accompanies stimulus‐induced IL‐1 posttranslational processing and human monocytes treated with ATP generate and release mature caspase‐1. ATP‐treated monocytes achieve a swollen morphology and do not produce mature caspase‐3; these traits are uncharacteristic of an apoptotic mechanism. Stimulus‐induced secretion of IL‐1β is disrupted by substitution of medium Cl ‐ with chaotropic anions such as I ‐ and by numerous anion transport inhibitors. These pharmacological agents block processing independently of the nature of the secretion stimulus, suggesting that a common downstream mechanism is engaged. Although sufficient to activate, the P2X 7 receptor (P2X 7 R) is not a necessary element of the secretory mechanism. KN‐62, an antagonist of P2X 7 R function, inhibits ATP‐induced IL‐1β posttranslational processing but does not inhibit processing induced by nigericin. Likewise, LPS‐activated peritoneal macrophages isolated from P2X 7 R‐deficient mice respond to nigericin and produce mature 17 kDa IL‐1β. On the other hand, the receptor‐deficient macrophages, in contrast to their wild‐type counterparts, do not respond to ATP. These findings highlight the unusual secretory requirements of IL‐1 and demonstrate that P2X 7 R activation represents one mechanism by which cytokine posttranslational processing can be initiated. Drug Dev. Res. 53:83–90, 2001. © 2001 Wiley‐Liss, Inc.