Characterization of a Secretase Activity for Placental Leucine Aminopeptidase

Placental leucine aminopeptidase (P-LAP) is believed to play an important role in the inactivation of small regulatory peptides. P-LAP exists in both membrane-bound and soluble forms and cDNA cloning has demonstrated that P-LAP is a type II membrane protein, which means that its soluble form is released by a specific proteolytic cleavage. In this report, we studied this process in COS7 cells. Inhibitors of serine or aspartic proteases did not affect the secretion of P-LAP, while EDTA and 1,10-phenanthroline inhibited it. In addition, we transfected P-LAP expression vectors that have point mutations of the cleavage site or deletion of the juxtamembrane stalk. Point mutations of the cleavage site resulted in significantly lower secretion of P-LAP. On the contrary, the distance to cleavage site showed no relation to P-LAP secretion. These results suggest that P-LAP secretase has a metalloprotease activity which depends on the amino acid sequence of the cleavage site.