PURIFICATION, CDNA CLONING, AND CHARACTERIZATION OF A NEW SERPIN WITHMEGAKARYOCYTE MATURATION ACTIVITY

A new member of the serine protease inhibitor (serpin) superfamily wit h megakaryocyte maturation activity was purified, and its cDNA was clo ned and characterized, The predicted amino acid sequence consisting of 380 residues was unique and was 38% identical to the serpin plasminog en activator inhibitor type 2 (PAI-2). The recombinant factor expresse d in Chinese hamster ovary cells showed species-specific activity on t he induction of megakaryocyte maturation in vitro. When injected into mice, the factor indeed elicited an increase in the number of platelet s in plasma. The sequence alignment indicated that the factor possesse d a lysine residue at the P-1 position, suggesting that it might funct ion as an inhibitor of Lys-specific proteases. Although we could not s how any inhibitory activities toward several known Lys specific protea ses, we detected the activity toward protease activity present in the culture supernatant of COLO 201 cells. These results suggested that th e protein might influence the maturation of megakaryocytes via action as a serpin.