Up-regulation of heme-binding protein 23 (HBP23) gene expression by lipopolysaccharide is mediated via a nitric oxide-dependent signaling pathway in rat Kupffer cells

Heme-binding protein 23 (HBP23) is a cytosolic protein that binds the proox idant heme with high affinity and has been implicated in the cellular prote ction against reactive oxygen species (ROS). Because lipopolysaccharide (LP S) stimulates macrophages to produce large amounts of ROS the gene expressi on of HBP23 was analyzed during treatment with LPS in cultured rat Kupffer cells (KC), HBP23 was constitutively expressed in KC and up-regulated on th e protein and messenger RNA (mRNA) level by LPS with a time response distin ct from that of TNF alpha, but in coordination with that of heme oxygenase- 1 (HO-1), which is the inducible isoform of the rate-limiting enzyme of hem e degradation. A parallel up-regulation of HBP23 and HO-1 mRNA by LPS was a lso observed in cultured peritoneal macrophages and peripheral blood monocy tes. HBP23 mRNA induction by LPS occurred on the transcriptional level as i ndicated by blocking with actinomycin D. The induction of HBP23 mRNA expres sion by LPS was preceded by that of the inducible nitric oxide synthase (iN OS) and the production of nitrite in KC, Treatment with the NOS inhibitor N -G-monomethyl L-arginine prevented HBP23 mRNA induction by LPS, which was r eversed by an excess of L-arginine. Both the nitric oxide (NO)-donor S-nitr oso-N-acetylpenicillamine and the peroxynitrite donor SIN-1 increased HBP23 mRNA expression. HBP23 mRNA induction by LPS was down-regulated by interle ukin 10 and transforming growth factor beta(1) with a NO-independent mechan ism. LPS-stimulated KC exhibited marked protection against the cytotoxicity mediated by H2O2 The data suggest that NO and peroxynitrite art major medi ators of the LPS-dependent up-regulation of HBP23 in KC.