Receptor-mediated induction of aminopeptidase A (APA) of human glomerular epithelial cells (HGEC) by glucocorticoids

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Abstract
Membrane-bound peptidases are critical regulators of peptide hormones. We therefore characterized aminopeptidase A (APA) activity in human glomerular epithelial cells (HGEC) and studied the control of its expression. APA, which splits off the N-terminal Asp from angiotensin II (AII), was present at the surface of HGECs (55% of the total enzyme). APA activity was calcium-dependent and was inhibited by amastatin. Treatment of HGECs by dexamethasone (DEX) increased ecto-APA activity in a dose- and time-dependent manner. Maximal increase of APA activity (x 2) occurred after treatment with 0.5 microM DEX for 5 days. HIgher concentrations (1-10 microM) of aldosterone (ALD) stimulated APA activity to a lesser extent (x 1.25). Actinomycin D and cycloheximide prevented and RU 38486, a glucocorticoid receptor antagonist, suppressed the DEX-induced increase in APA activity. These results indicate that AII availability at glomerular receptor sites may be reduced by DEX and suggest a role for glucocorticoids in AII-dependent changes of glomerular filtration rate.