An immunocytochemical study on distinct intracellular localization of cathepsin E and cathepsin D in human gastric cells and various rat cells.

Immunocytochemical localization of two distinct intracellular aspartic proteinases, cathepsins E and D, in human gastric mucosal cells and various rat cells was investigated by immunogold technique using discriminative antibodies specific for each enzyme. Cathepsin D was exclusively confined to primary or secondary lysosomes in almost all the cell types tested, whereas cathepsin E was not detected in the lysosomal system. The localization of cathepsin E varied with different cell types. Microvillous localization of cathepsin E was found in the intracellular canaliculi of human and rat gastric parietal cells, rat renal proximal tubule cells, and the bile canaliculi of rat hepatic cells. The immunolocalization of each enzyme in gastric cells were essentially the same in humans and rats. In the gastric feveolar epithelial cells and parietal cells, definite immunolabeling for cathepsin E was observed in the cytoplasmic matrix, the cisternae of the rough endoplasmic reticulum, and the dilated perinuclear envelope. In rat kidney, cathepsin E was detected only in the proximal tubule cells, while cathepsin D was found mainly in the lysosomes of the distal tubule cells but not in those of the proximal tubule cells. These results clearly indicate the distinct intracytoplasmic localization of cathepsins E and D and suggest the possible involvement of cathepsin E in extralysosomal proteolysis that is related to specialized functions of each cell type.