Functional Aspects of Cathepsin E: Is it an Embryonic or Fetal Type of Aspartic Proteinase?

Abstract

Cathepsin E is now accepted as a unique member of mammalian aspartic proteinases, in that it is non-secretory and non-lysosomal (1). In rodents, the enzyme is distributed in the stomach, bladder, myeloid and lymphoid tissues as well as mature blood cells (2). The functional role of cathepsin E is not yet established, but recent studies have raised a possibility that the enzyme may be involved in the proteolytic processing of bioactive peptides (3,4). We found, however, that the distribution of the enzyme in mammalian blood cells is species-specific (5). Furthermore, our preliminary data showed that cathepsin E was not detectable in cultured human, bovine and rat endothelial cells. We then extended our study to specify its role in the stomach, the main distributional site of the enzyme. We demonstrate here an early appearance of cathepsin E in developing rat stomachs, as revealed by immunochemical and immunohistochemical examinations. Attention was paid for a possible functional association with the developmental differentiation of the gastric gland and for its possible role as a digestive enzyme in the fetal stomach.