MOLECULAR-CLONING AND EXPRESSION OF SERUM CALCIUM-DECREASING FACTOR (CALDECRIN)

We previously reported on the purification of a serum calcium decreasi ng factor, referred to as caldecrin, from porcine pancreas, that is th ought to be a serine protease (Tomomura, A., Fukushige, T., Noda, T., Noikura, T., and Saheki, T. (1992) FEBS Lett. 301, 277-281). In the pr esent study, we purified caldecrin from rat pancreas and determined it s primary structure by cDNA cloning, The predicted caldecrin protein i s presumed to be synthesized as a preproenzyme of 268 amino acids with a signal peptide of 16 amino acids and an activation peptide of 13 am ino acids, and is, with the exception of a central region, almost iden tical to the reported rat pancreatic elastase IV sequence. The caldecr in gene is selectively expressed in the pancreas, as judged by Norther n blot analysis. After expression in BMT-10 cells, immunoreactive cald ecrin was found in the culture supernatant, and it inhibited the parat hyroid hormone-stimulated Ca-45 release from cultured fetal long bones , Catalytic site mutants were synthesized in a baculovirus system, and recombinant mutants also decreased the serum calcium level of mice. T hese data implicate caldecrin, a protease closely related to elastase IV, in the regulation of blood calcium levels.