Biosynthesis of intestinal microvillar proteins. Expression of aminopeptidase N along the crypt-villus axis

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Abstract
The expression of pig small-intestinal aminopeptidase N (EC 3.4.11.2) along the cryt-villus axis was studied in tangential sections of [35S]-methionine-labeled, organ-cultured explants. The only detectable molecular forms of aminopeptidase N along the crypt-villus axis were polypeptides of MW 140,000 and 166,000, representing the enzyme in a transient and mature form, respectively. The synthesis was at a very low level in the crypt region in experiments with labeling periods ranging from 10 min-3 h. Crypt cells are not fully committed to the expression of aminopeptidase N, either in its mature or in any other immunoreactive molecular form. The expression of aminopeptidase N was markedly stimulated by dexamethasone (1 .mu.g/ml). During labeling periods of 3 h, dexamethasone caused an .apprx. 3-fold increae in the expression of the enzyme in the crypt cells and a moderate increase of .apprx. 20% in the villus cells. Whereas the latter could possibly be ascribed to a general protective effect of dexamethasone on villus architecture, these experiments indicated that crypt cells of mucosa from adult individuals exhibited the same sensitivity to glucocorticoids as the intestinal epithelium did during the prenatal and early postnatal phase.