Cytokine-Stimulated GTP Cyclohydrolase I Expression in Endothelial Cells Requires Coordinated Activation of Nuclear Factor-κB and Stat1/Stat3

Endothelial production of nitric oxide (NO) is dependent on adequate cellular levels of tetrahydrobiopterin (BH4), an important cofactor for the nitric oxide synthases. Vascular diseases are often characterized by vessel wall inflammation and cytokine treatment of endothelial cells increases BH4 levels, in part through the induction of GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme for BH4 biosynthesis. However, the molecular mechanisms of cytokine-mediated GTPCH I induction in the endothelium are not entirely clear. We sought to investigate the signaling pathways whereby cytokines induce GTPCH I expression in human umbilical vein endothelial cells (HUVECs). Interferon-γ (IFN-γ) induced endothelial cell GTPCH I protein and BH4 modestly, whereas high-level induction required combinations of IFN-γ and tumor necrosis factor-α (TNF-α). In the presence of IFN-γ, TNF-α increased GTPCH I mRNA in a manner dependent on nuclear factor-κB (NF-κB), as this effect was abrogated by overexpression of a dominan...