A new intracellular serine protease inhibitor expressed in the rat pituitary gland complexes with granzyme B

We have cloned a novel serpin (raPIT5a) from a rat pituitary cDNA library w hich is structurally related to members of the ovalbumin subfamily of serin e protease inhibitors. This new cDNA encodes a 374-amino acid protein, desi gnated raPIT5a. raPIT5a was expressed in specific cells in the intermediate and anterior lobes of the pituitary. Recombinant raPIT5a was not secreted suggesting raPIT5a functions to inhibit intracellular proteases, Recombinan t raPIT5a formed an SDS-stable complex with human granzyme B, a serine prot ease which induces apoptosis by activating members of the caspase enzyme fa mily. These data suggest raPIT5a may have a role in regulating granzyme B o r related enzymes and apoptosis in the pituitary gland. (C) 1998 Federation of European Biochemical Societies.