Production and mechanism of secretion of interleukin-1β from the marine fish gilthead seabream

Abstract

Mammalian interleukin-1β (IL-1β) is a secretory cytokine lacking a signal peptide, which does not follow the classical endoplasmic reticulum to Golgi pathway of secretion. Its post-translational processing by IL-1β-converting enzyme (ICE) and subsequent release from activated macrophages requires ATP acting on P2X 7 receptors. Little information is available on the production and release of fish IL-1β, but the IL-1β gene sequences reported to date lack a conserved ICE recognition site. We show for the first time that lipopolysaccharide (LPS)/macrophage-activating factor/bacterial DNA (VaDNA)-primed immune cells of the marine fish gilthead seabream ( Sparus aurata) accumulate intracellular IL-1β as a ∼30 kDa polypeptide (proIL-1β). The combination of LPS and VaDNA was found to be synergistic, suggesting that each ligand is recognized by a different pattern recognition receptor. More importantly, addition of extracellular ATP does not promote IL-1β secretion by immune cells and fails to induce phosphatidylserine flip. In contrast, gilthead seabream SAF-1 fibroblasts shed microvesicles containing a 22 kDa IL-1β form within 30 min of activation with ATP. Notably, the post-translational processing of IL-1β by SAF-1 cells is abrogated by a specific ICE inhibitor.