Molecular characterization of three rat liver serine‐protease inhibitors affected by inflammation and hypophysectomy

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Abstract
Rat hepatocytes have the potential to secrete three similar acidic glycoproteins, serine protease inhibitors 1, 2 and 3 (SPI‐1, SPI‐2, SPI‐3), recognized by the same antibodies. They were synthesized as precursors of comparable sizes (45 kDa), which were post‐translationally modified by N‐glycosylation at three (SPI‐3) or four (SPI‐1 and SPI‐2) sites. This appeared to account for the size difference of mature proteins. The mRNA sequences, derived from cDNA clones, displayed a high degree of similarity (70–90%), except the sequence of the antiprotease‐reactive centers which were completely divergent. SPI‐1 and SPI‐2 mRNAs were of similar sizes (1.8 kb), and were smaller than that of SPI‐3 (2.2 kb); the difference corresponded to a longer, 3′‐end untranslated sequence. Production of SPI‐1 and SPI‐2, which was constitutive in the normal animal, could be abolished by hypophysectomy and was strongly decreased during acute inflammation. In contrast, production of SPI‐3, which was barely detectable in normal rats, was transiently induced during inflammation.