REGULATION OF EXPRESSION OF SURFACE AMINOPEPTIDASE-N IN HUMAN GLOMERULAR MESANGIAL CELLS .2. EFFECT OF CYCLIC-NUCLEOTIDES, GROWTH-FACTORS AND MITOGENS

Aminopeptidase N of human glomerular mesangial cells is an ectoenzyme. Control of its expression by mitogens has been demonstrated. Aminopep tidase N activity was increased after 72 h of treatment with 8-bromo-c AMP and two cAMP-stimulating agents, forskolin and isobutylmethylxanth ine (IBMX). IBMX (100 mu M), a phosphodiesterase inhibitor, stimulated aminopeptidase N activity by 40%. Stimulation by cAMP and forskolin w as less marked, 25 and 28%, respectively. Phorbolmyristate acetate (PM A) treatment increased enzyme activity by 80%; however, after treatmen t with both PMA and cAMP or PMA and forskolin, aminopeptidase N activi ty increased by 178 and 190%, respectively. Bacterial lypopolysacchari de (LPS) moderately stimulated surface aminopeptidase N activity; LPS potentiated the effect of PMA on enzyme activity. Thrombin (0.1-5 U/ml ) also stimulated aminopeptidase N activity, by 27% at a concentration of 2.5 U/ml. The effects of thrombin and cAMP or forskolin were addit ive. Dexamethasone (0.1-10 mu M) treatment for up to 6 days was withou t effect on aminopeptidase N expression. A short treatment (72 h) with interferon-gamma (1-5,000 U/ml) increased enzyme activity by 26% The effect of insulin growth factor I (50 ng/ml) and endothelin (0.1-100 n M) on aminopeptidase N activity was not significant. Serum withdrawal from the culture medium was accompanied by a significant increase in e nzyme activity in the 48-hour culture. This study shows that expressio n of mesangial cell aminopeptidase N is regulated by mitogenes, cAMP a nd c-AMP-stimulating agents acting in concert.