The transcriptional factor Bach1 forms a heterodimer with small Maf family, and functions as a repressor of the Maf recognition
element (MARE) in vivo. To investigate the involvement of Bach1 in the
heme-dependent regulation of the expression of the
alpha-globin gene, human
erythroleukemia K562 cells were cultured with
succinylacetone (SA), a
heme biosynthetic inhibitor, and the level of
alpha-globin mRNA was examined. A decrease of
alpha-globin mRNA was observed in SA-treated cells, which was restored by the addition of
hemin. The
heme-dependent expression of
alpha-globin occurred at the transcriptional level since the expression of human
alpha-globin gene promoter-reporter gene containing hypersensitive site-40 (HS-40) was decreased when K562 cells were cultured with SA.
Hemin treatment restored the decrease of the promoter activity by SA. The regulation of the HS-40 activity by
heme was dependent on the NF-E2/AP-1 (NA) site, which is similar to MARE. The NA site-binding activity of Bach1 in K562 increased upon SA-treatment, and the increase was diminished by the addition of
hemin. The transient expression of Bach1 and mutated Bach1 lacking CP motifs suppressed the HS-40 activity, and cancellation of the repressor activity by
hemin was observed when wild-type Bach1 was expressed. The expression of NF-E2 strengthened the restoration of the Bach1-effect by
hemin. Interestingly, nuclear localization of Bach1 increased when cells were treated with SA, while
hemin induced the nuclear export of Bach1. These results indicated that
heme plays an important role in the induction of
alpha-globin gene expression through disrupting the interaction of Bach1 and the NA site in HS-40 enhancer in erythroid cells.