Expression of a novel human ornithine decarboxylase-like protein in the central nervous system and testes

Ornithine decarboxylase (ODC) is the key enzyme of polyamine synthesis. The physiological activity of ODC is associated with cell proliferation, and h igh ODC activities are encountered in rapidly growing cancer cells. We have cloned a cDNA for a novel human protein that is 54% identical to ODC and 4 5% identical to antizyme inhibitor (AZI). mRNA for ODC-paralogue (ODC-p) wa s found only in the central nervous system and testes, suggesting a role in terminal differentiation rather than cell proliferation. ODC-p occurs at l east in eight alternatively spliced forms. In vitro translated ODC-p did no t decarboxylate ornithine, whereas, in vivo, one splice variant exerted mod est ODC-like activity upon expression in COS-7 cells. ODC-p has a unique mu tation in cysteine 360, where this ornithine decarboxylase reaction-directi ng residue is substituted by a valine. This substitution might lead to an e nzymatic reaction that differs from typical ODC activity. ODC-p might also function as a brain- and testis-specific AZI. (C) 2001 Academic Press.