Formation of active IL-1β from pro-IL-1β catalyzed by stratum corneum chymotryptic enzyme in vitro

Abstract

Interleukin 1β (IL-1β) is produced as a biologically inactive 31 kD precursor, which is converted to the active 18 kD form by proteolytic processing. Keratinocytes express IL-1β but not the active form of the specific IL-1β converting enzyme (ICE). We have recently presented evidence that IL-1β activation in human epidermis occurs via an alternative mechanism involving hitherto unknown proteases. We asked whether stratum corneum chymotryptic enzyme (SCCE), which is a serine protease specifically expressed in keratinizing squamous epithelia, can act as an IL-1β activator in vitro. Recombinant human pro-IL-1β was incubated with recombinant SCCE, and the reaction products were characterized as regards molecular size and ability to induce expression of E-Selectin in human umbilical cord endothelial cells. SCCE caused degradation of pro-IL-1β and the accumulation of a component with electrophoretic mobility slightly lower than recombinant mature IL-1β. Whereas incubation mixtures with pro-IL-1β, which had been incubated in the absence of SCCE, or with SCCE, which had been incubated in the absence of pro-IL-1β, did not induce expression above baseline levels of E-Selectin, pro-IL-1β which had been incubated with SCCE induced a significant increase in E-Selectin expression. This effect could be abolished by neutralizing antibodies to IL-β, but not by antibodies to IL-1β. In addition to IL-1β activation, SCCE also appeared to be able to catalyze a further degradation of IL-1β, leading to a loss of biological activity. We conclude that SCCE is a potential candidate for being responsible for IL-1β activation in human epidermis.