CLONING, SEQUENCE-ANALYSIS, AND DISTRIBUTION OF RAT METALLOCARBOXYPEPTIDASE-Z

A cDNA encoding human carboxypeptidase Z (CPZ), a novel metallocarboxy peptidase, was recently cloned (Song and Fricker, J. Biol. Chem., 272, 1054, 1997). In the present study, a cDNA encoding the rat homolog of CPZ was identified, As with the human form, rat CPZ contains an N-ter minal domain of 120 amino acids that has 20% to 30% amino acid identit y with the ''frizzled'' domain found on proteins that interact with Wn t, a protein involved in tissue polarity in early embryogenesis, Seque nce analysis showed rat and human CPZ to be highly conserved within th e frizzled domain (77% amino acid identity), the carboxypeptidase doma in (91%), and the C-terminal 28 residues (78%), The entire rat CPZ pro tein has high sequence similarity with human CPZ (81% amino acid ident ity), moderate sequence similarity to human carboxypeptidase N (45%), human carboxypeptidase E (41%), and human carboxypeptidase M (33%), an d less sequence similarity with other metallocarboxypeptidases. Northe rn blot analysis showed rat CPZ mRNA to be abundant in the placenta, w ith low to moderate levels in the brain, lung, thymus, and kidney. The BRL3A rat liver cell line and the PC12 rat adrenal cell line express high levels of CPZ mRNA, In situ hybridization analysis indicated that CPZ is expressed only in specific cell types. For example, in the bra in, CPZ mRNA is present in leptomeningeal cells, but not in the majori ty od other cell types. This distribution in leptomeningeal cells is s hared by AEBP1, a recently reported member of the metallocarboxypeptid ase gene family. However, the distribution of CPZ and AEBP1 differ in pituitary and thyroid. Taken together, these studies suggest that CPZ functions in a range of cell types.