Induction of the heme oxygenase-1 gene by metalloporphyrins

Induction of expression of heme oxygenase-1 (HO-1) has been studied in prim ary cultures of chick embryo liver cells and in the LMH line of avian hepat oma cells. Cells were transiently transfected with selected constructs cont aining portions of the 5'-untranslated (promoter) region of the HO-1 gene l inked to luciferase as reporter gene. LMH cells that had been stably transf ected with selected wild type or mutant constructs were also studied. Metal loporphyrins, especially Fe protoporphyrin (heme) and Co protoporphyrin str ongly induced luciferase expression in both types of transfected cells. Low concentrations of Zn mesoporphyrin, an inhibitor of HO activity, exerted a synergistic effect on heme-, but not Co protoporphyrin-dependent induction . The antioxidant and -SH donor N-acetyl cysteine had little effect on the metalloporphyrin-dependent inductions of HO-1, in contrast to its marked in hibitory effect on the sodium arsenite dependent induction of the HO-1 gene . Deletional analysis showed that the key element(s) required for the metal loporphyrin-dependent induction of HO-1 is located between -3.6 and -5.6 kb upstream of the transcription starting point. Data from electrophoretic mo bility shift and site-directed mutagenesis experiments excluded a role for consensus AP-1 binding elements at -1576, -3647, or -4578 in the inductions produced by heme or Co protoporphyrin, (C) 2000 Academic Press.