Heme oxygenase-1 inhibits the expression of adhesion molecules associated with endothelial cell activation via inhibition of NF-kappaB RelA phosphorylation at serine 276.
Heme oxygenase-1 (HO-1; encoded by the Hmox1 gene) catalyzes the degradation of free heme into biliverdin, via a reaction that releases iron (Fe) and carbon monoxide. We report that HO-1 down-regulates the proinflammatory phenotype associated with endothelial cell (EC) activation by reducing intracellular nonprotein-bound Fe (labile Fe). EC isolated from Hmox1(-/-) mice have higher levels of intracellular labile Fe and reactive oxygen species (ROS) as compared with EC isolated from Hmox1(+/+) mice. Basal and TNF-induced expression of VCAM-1, ICAM-1, and E-selectin were increased in Hmox1(-/-) vs Hmox1(+/+) EC, an effect reversed by Fe chelation using deferoxamine mesylate (DFO). Fe chelation inhibits TNF-driven transcription of Vcam-1, Icam-1, and E-selectin, as assessed using luciferase reporter assays. This effect is associated with inhibition of the transcription factor NF-kappaB via a mechanism that is not associated with the inhibition of IkappaBalpha phosphorylation/degradation or NF-kappaB (i.e., RelA) nuclear translocation, although it affects very modestly NF-kappaB binding to DNA kappaB consensus sequences in the Vcam-1 and E-selectin promoters. HO-1 inhibits NF-kappaB (i.e., RelA) phosphorylation at Ser(276), a phosphoacceptor that is critical to sustain TNF-driven NF-kappaB activity in EC. This effect was mimicked by Fe chelation as well as by antioxidants (N-acetylcysteine). In conclusion, we demonstrate a novel mechanism via which HO-1 down-modulates the proinflammatory phenotype of activated EC, i.e., the inhibition of RelA phosphorylation at Ser(276).
Seldon
Mark P
MP
Instituto Gulbenkian de Ciência, Apartado 14, Oeiras, Portugal.
Silva
Gabriela
G
Pejanovic
Nadja
N
Larsen
Rasmus
R
Gregoire
Isabel Pombo
IP
Filipe
Josina
J
Anrather
Josef
J
Soares
Miguel P
MP
D000818:Animals; D015815:Cell Adhesion Molecules / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D002478:Cells, Cultured; D015536:Down-Regulation / Q000276:immunology; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D005290:Ferric Compounds / Q000276:immunology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology*; D051547:Heme Oxygenase-1 / Q000172:deficiency / Q000276:immunology* / Q000494:pharmacology; D007249:Inflammation; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000276:immunology; D010766:Phosphorylation / Q000187:drug effects; D012694:Serine / Q000187:drug effects / Q000276:immunology*; D051996:Transcription Factor RelA / Q000187:drug effects / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D019010:Vascular Cell Adhesion Molecule-1 / Q000096:biosynthesis / Q000187:drug effects
D015815:Cell Adhesion Molecules; D005290:Ferric Compounds; D016328:NF-kappa B; D051996:Transcription Factor RelA; D019010:Vascular Cell Adhesion Molecule-1; D012694:Serine; D051547:Heme Oxygenase-1