Glucocorticoids and protein kinase C regulate neutral endopeptidase 24.11 in human vascular smooth muscle cells

Neutral endopeptidase 24.11 (NEP) degrades vasoactive peptides, including natriuretic peptides, kinins, angiotensins, and endothelins. It contributes to the regulation of vascular tone and body fluid homeostasis. In the present study the expression of NEP was investigated in cultured human smooth muscle cells derived from umbilical veins (HSMC) and human coronary arteries (HCSMC). A constitutive NEP expression was found in growing and starved smooth muscle cells and was about 4 fold higher than in endothelial cells derived from umbilical veins. Treatment of smooth muscle cells with dexamethasone (0.01-0.1 microM Dex) and with the protein kinase C activator, phorbol myristate acetate (0.1 microM PMA), increased NEP mRNA by 3-4 fold and two fold, respectively. Dexamethasone (0.1 microM) and prednisolone (0.1 microM) increased protein concentrations of NEP and NEP-activity after 3 days and continued to increase at 5 days, whereas PMA induced maximal increase of NEP concentrations after 48 hours. The effect of dexamethasone was concentration-dependent and was completely abolished by cycloheximide (10 microM), a protein synthesis inhibitor. The effect of PMA on NEP protein was completely blocked by protein kinase C inhibitors, calphostin C and H7 (both 10 microM). NEP 24.11 is constitutively expressed in human smooth muscle cells from umbilical veins and coronary arteries and is upregulated by glucocorticoids and by protein kinase C activation in these cells.