Gene regulation and extracellular functions of procathepsin L

Cathepsin L, a lysosomal cysteine proteinase, belongs to the papain family. This proteinase is different from the other members of the mammalian papain family cysteine proteinase in the following ways: (i) The cathepsin L gene is activated by a variety of growth factors and activated oncogenes. (ii) Procathepsin L, a precursor form of cathepsin L is secreted from various cells. (iii) The mRNA level of cathepsin L is related to the in vivo metastatic potential of the transformed cells. Thus, the regulation of the cathepsin L gene and the extracellular functions of secreted procathepsin L are tightly coupled. In this review, we describe these two points, which have recently been addressed in our laboratory.