Heme oxygenase catalyzes the first and rate-controlling step of
heme catabolism. Induction of
heme oxygenase-1 can be caused by numerous factors, including
heme, other
metalloporphyrins, transition
metal ions, heat shock, ultraviolet light,
phorbol esters,
sodium arsenite, and
phenylarsine oxide (PAO). Induction of this
enzyme may protect cells from oxidative damage. Using
heme oxygenase-1 promoter/reporter gene constructs, we have previously reported that the
sodium arsenite-mediated induction of
heme oxygenase-1 in chick embryo liver cells and chicken
hepatoma (LMH) cells involves an
AP-1 element. We have now investigated whether the PAO-mediated induction of
heme oxygenase-1 also involves an
AP-1 element. Primary cultures of chick embryo liver cells were transiently transfected with
heme oxygenase-1 promoter/reporter gene constructs, treated with PAO, and reporter gene activities were measured. We found that the PAO-mediated increase in reporter gene activity was dose- and time-dependent. This activity was decreased by prior treatment with
N-acetylcysteine. Studies with mutated constructs showed that both an
AP-1 element and a
metal responsive
element are involved in the PAO-mediated induction of the
heme oxygenase-1 reporter construct. Electrophoretic mobility shift assays showed that
nuclear proteins from PAO-treated cells had increased binding to an
AP-1 probe, and that this increase was abrogated by
N-acetylcysteine. These findings support the hypothesis that the PAO-mediated induction of
heme oxygenase-1 is caused by activation of
AP-1 and MRE/cMyc elements and may involve
nuclear proteins whose states of phosphorylation determine binding to regulatory elements, and thus the level of expression of
heme oxygenase-1.