Hydroxyurea induces the eNOS-cGMP pathway in endothelial cells

Hydroxyurea is a cell-cycle-specific drug that has been used to treat myeloproliferative diseases and sickle cell anemia. We have recently shown that hydroxyurea, like nitric oxide (NO)-donor compounds, increased cGMP levels in human erythroid cells. We show now that hydroxyurea increases endothelial-cell production of NO; this induction of NO in human umbilical vein endothelial cells (HUVECs) and human bone marrow endothelial cell line (TrHBMEC) is blocked by competitive inhibitors of NO synthase (NOS), such as N-G-nitro-L-arginine-methyl ester (L-NAME) and N-G-nitro-L-arginine. It is dependent on cAMP-dependent protein kinase (PKA) and protein kinase B (PKB/Akt) activity. We found that hydroxyurea dose- and time-dependently induced rapid and transient phosphorylation of eNOS at Ser1177 in a PKA-dependent manner; inhibitors of PKB/Akt could partially abrogate this effect. In addition, hydroxyurea induced cAMP and cGMP levels in a dose-dependent manner, as well as levels of intracellular calcium in HUVECs. These studies established an additional mechanism by which rapid and sustained effects of hydroxyurea may affect cellular NO levels and perhaps enhance the effect of NO in myeloproliferative diseases.