The hematotoxicity of
benzene, a human leukemogen, has been postulated to be mediated by reactive metabolites and involve cell damage caused by
reactive oxygen species. Because expression of the
transcription factors AP-1 and
NF-kappaB is sensitive to the redox state in eukaryotic cells, the
DNA binding activity of
AP-1 and
NF-kappaB was examined in HL-60 promyeloid
leukemia cells exposed to trans,trans-
muconaldehyde, a microsomal hematotoxic metabolite of
benzene. There was little
AP-1 binding activity in nuclear extracts from control HL-60 cells based on electrophoretic mobility shift assays. Exposure to 0.1 microM MUC for 4 h resulted in significantly increased levels of
nuclear protein with high sequence specificity for the consensus
AP-1 sequence. In addition, electrophoretic mobility shift assays showed a strong increase in the binding of
a factor to the
NF-kappaB site. The latter was highest in nuclear extracts from HL-60 cells treated with 1.0 microM
muconaldehyde and cultured for 4 h. Exposure of HL-60 cells to
muconaldehyde resulted in an increase in c-fos and c-jun
mRNA levels. Western blot analysis showed that the
protein levels of c-jun increased in HL-60 cells treated with 1 microM
muconaldehyde and cultured for 4-6 h and subsequently decreased gradually. Increased
AP-1 binding was observed in bone marrow cells from B6C3F1 mice 2 h after administration of 440 mg/kg
benzene. We suggest that increased gene expression of
NF-kappaB and
AP-1 binding activity and up-regulation of c-fos and c-jun may play a role in the mechanism of
benzene leukemogenesis.