Effects of serine protease inhibitor, tame, on IL-1β in LPS-stimulated human monocytes: Relationship between synthesis and release of a 33-kDa precursor and the 17-kDa biologically active species

LPS stimulation of human monocytes in vitro induced release of the 17-kDa mature IL-1β (mIL-1β) but did not result in release of precursor IL-1β (pIL-1β). In contrast, the presence of a serine protease inhibitor, Nα-(p-toluene sulfonyl)-L-arginine methyl ester (TAME; 10 mM) for 6 or 18 h was associated with the LPS-stimulated release of the 33-kDa pIL-1β as well. These effects were initially discerned from observations that the fraction of the total IL-1β produced (as detected by ELISA) that was released from monocytes increased in the presence of TAME, and immunoblot assays confirmed that this fraction was predominantly 33-kDa IL-1β. A global decrease in monocyte protein synthesis was also observed after prolonged (18-h) exposure to TAME and was associated with a decrease in IL-1β synthesis, predominantly affecting 31-kDa pIL-1β, and a dose-dependent inhibition of TNF-α production. Parallel examination of lactate dehydrogenase (LDH) release indicated thatpIL-1β release was unrelated to cell lysis. These results demonstrate that TAME-inhibitable serine proteases are probably involved in the production and eventual proteolysis of the 33-kDa pIL-1β in situ but are probably not mechanistically related to either maturation of the IL-1β molecule or signaling of IL-1β release. IL-1β release appears to be dependent on the amount of total IL-1β synthesized. Serine proteolysis may constitute a degradative pathway for excess precursor, which, if interfered with, could result in release of the higher-molecular-weight forms of IL-1β.