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

Abstract

The expression of pig small‐intestinal aminopeptidase N (EC 3.4.11.2) along the crypt‐villus axis was studied in tangential sections of [35S]‐methionine‐labelled, organ‐cultured explants. The only detectable molecular forms of aminopeptidase N along the crypt‐villus axis were polypeptides of Mr 140000 and 166000, 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 labelling periods ranging from 10 min to 3 h. These findings indicate that 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 μg/ml). During labelling periods of 3 h, dexamethasone caused an approximately threefold increase in the expression of the enzyme in the crypt cells and a moderate increase of about 20% in the villus cells. Whereas the latter can possibly be ascribed to a general protective effect of dexamethasone on villus architecture, these experiments indicate that crypt cells of mucosa from adult individuals exhibit the same sensitivity to glucocorticoids as does the intestinal epithelium during the prenatal and early postnatal phase.

Inhibitory effects of glycopyrronium, formoterol, and budesonide on coronavirus HCoV-229E replication and cytokine production by primary cultures of human nasal and tracheal epithelial cells

“…There was a reduction in the HCoV-229E titer and CD13 expression in HNE cells pretreated with cAMP at similar levels to those secreted into the supernatant when cells were treated with formoterol. The inhibitory effects of formoterol on CD13 expression were consistent with the results of a previous report by Danielsen et al, which found that CD13 expression in the intestinal mucosa was decreased by forskolin, an activator of adenylate cyclase [25], which is activated by formoterol [26]. Therefore, formoterol may decrease HCoV-229E replication partly by modulating receptor expression via cAMP production.…”

Biosynthesis of intestinal microvillar proteins. Evidence for an intracellular sorting taking place in, or shortly after, exit from the Golgi complex

“…The rather long transport time, preceding its microvillar expression (about 60 min), together with the clear separation in SDSjPAGE of its transient and mature forms, made aminopeptidase N a suitable probe for studying the intracellular sorting of a plasma membrane protein. In addition, since this enzyme constitutes about 1.5% of the total protein synthesis in the enterocyte [32], it is a mdjor component whose molecular forms of M , 166000 and 140000 are predominant and easily recognized bands in the high-M, region in SDS/ PAGE. After 30 min of labelling, the majority of newly synthesized aminopeptidase N (> 95%) was still in the transient form, i.e.…”

“…In addition, since this enzyme constitutes about 1.5% of the total protein synthesis in the enterocyte [32], it is a mdjor component whose molecular forms of M , 166000 and 140000 are predominant and easily recognized bands in the high-M, region in SDS/ PAGE. After 30 min of labelling, the majority of newly synthesized aminopeptidase N (> 95%) was still in the transient form, i.e.…”

The role of feline aminopeptidase N as a receptor for infectious bronchitis virus

“…APN is expressed on the plasma membranes of granulocytes [2,36], lymphocytes and monocytes [26,30,31,35]. It is also expressed on non-hematopoetic tissue including fibroblasts [35], synaptic membranes in the central nervous system [6], epithelial cells from the renal proximal tubules and the intestinal brush border, and endothelial and epithelial cells of the respiratory tract [8,12,34,35]. Most recently APN has been isolated from chicken embryo yolk [32] and chicken intestine [14].…”