Transcriptional regulation of the GTP cyclohydrolase I gene via the NF-κB pathway by bacterial and viral immune stimulants.

Tetrahydrobiopterin (BH4) is an essential cofactor for biosynthesis of monoamines and nitric oxide. An excess of BH4 in infiltrated macrophages was reported to cause pain, while a certain level of BH4 is essential for cell survival and proliferation. GTP cyclohydrolase I (GCH) is a rate-limiting enzyme for the de novo synthesis of BH4. Our previous study showed that GCH expression was elevated by an enhancer region containing the C/EBP and Ets binding motifs in macrophage-like RAW264.7 cells when stimulated with lipopolysaccharide (LPS). In this study, we showed that poly(I:C) and R848, Toll-like receptors ligands for RNA viruses, increased GCH expression and BH4 levels in RAW264.7 cells as well as bacterial LPS. We examined the intracellular signaling pathway for the induction of the Gch gene, and found that inhibitors for the NF-κB pathway suppressed the GCH expression by these stimuli. We for the first time identified the region required for LPS-induced GCH expression to be the 5'-untranslted region of exon 1 consisting of 149 bp using a reporter experiment. We also demonstrated that the expression of GCH with LPS was strongly suppressed by an inhibitor of NF-κB in mouse intraperitoneal macrophages in vivo.