Tissue kallikrein mK13 is a candidate processing enzyme for the precursor of interleukin-1β in the submandibular gland of mice

Abstract

By using Western blot analysis, high levels of 17.5- and 20-kDa interleukin-1β (IL-1β) proteins were detected in the submandibular gland (SMG) of mice. Despite this fact, the amount of pro-IL-1β protein, a precursor of IL-1β, with a molecular size of 35 kDa in this tissue was below the detectable level, although strong expression of pro-IL-1β mRNA was observed. A large amount of 17.5-kDa IL-1β also appeared in the saliva of mice injected with lipopolysaccharide, suggesting that this IL-1β is a secretory form produced by the SMG. The protein for IL-1β-converting enzyme, a processing enzyme for pro-IL-1β, was expressed only at a low level in the SMG as compared with its level in various epithelial tissues or lipopolysaccharide-stimulated macrophages. On the other hand, mK1, mK9, mK13, and mK22, members of the kallikrein family, were detected strongly in the SMG but not in other tissues. By incubation with mK13, but not with mK1, mK9, or mK22, the 35-kDa pro-IL-1β was cleaved into two major products with molecular masses of 17.5 and 22 kDa, and production was inhibited by phenylmethylsulfonyl fluoride, a serine protease inhibitor, but not by IL-1β-converting enzyme inhibitors. A peptide segment corresponding to amino acid residues 107-121 of mouse pro-IL-1β ( 107WDDDDNLLVCDVPIR) was cleaved by incubation with mK13, generating two peptides, 107WDDDDNL and 114LVCDVPIR. Therefore, kallikrein mK13 would appear to hydrolyze pro-IL-1β between its Leu 113 and Leu114 residues. The results of immunohistochemistry and an autonomic therapy experiment showed that IL-1β and kallikrein mK13 were co-localized in the secretory granules of granular convoluted tubular cells. Our present results thus suggest kallikrein mK13 is a plausible candidate for the processing enzyme for pro-IL-1β in the SMG of mice. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.