Expression of cathepsin E in epithelial cells of the normal glandular stomach and small intestine, intestinal metaplasia, stomach and small intestinal tumors, was investigated in rats treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Immunohistochemically, parietal cells were found to be moderately positive while surface mucous and pyloric gland cells demonstrated marked staining. Intestinal metaplastic glands in the stomach and normal small intestinal epithelial cells did not have any cathepsin E reactivity although some regenerative small intestinal epithelium proved positive. Histochemical staining for mucin demonstrated all stomach tumors (adenomatous hyperplasias and well-differentiated adenocarcinomas) to be mainly comprised of gastric epithelial type cells (pyloric gland and surface mucous cells), with intestinal epithelial type cells (goblet and intestinal absorptive cells) being only occasional findings. Almost all of the gastric epithelial type cells showed cathepsin E reactivity in their cytoplasm while the intestinal epithelial cell type cells were mainly consisted of cathepsin E negative one like those in small intestinal cancers. Catepsin E may thus be a useful marker for cell differentiation of stomach tumors and their intestinalization. Cancers arising in the small intestine consisted of intestinal epithelial cell type cells, but no stomach tumors consisted predominantly of this type, so that there was no suggestion of any derivation from intestinal metaplasias in rats.
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