The effects of 1,4-benzoquinone on c-Myb and topoisomerase II in K-562 cells.
Exposure to benzene, a ubiquitous environmental pollutant, has been linked to leukemia, although the mechanism of benzene-initiated leukemogenesis remains unclear. Benzene can be bioactivated to toxic metabolites such as 1,4 benzoquinone (BQ), which can alter signaling pathways and affect chromosomal integrity. BQ has been shown to increase the activity of c-Myb, which is an important transcription factor involved in hematopoiesis, cell proliferation, and cell differentiation. The c-Myb protein has also been shown to increase topoisomerase IIalpha (Topo IIalpha) promoter activity specifically in cell lines with hematopoietic origin. Topo IIalpha is a critical nuclear enzyme that removes torsional strain by cleaving, untangling and religating double-stranded DNA. Since Topo IIalpha mediates DNA strand breaks, aberrant Topo IIalpha activity or increased protein levels may increase the formation of DNA strand breaks, leaving the cell susceptible to mutational events. We hypothesized that BQ can increase c-Myb activity, which in turn increases Topo IIalpha promoter activity resulting in increased DNA strand breaks. Using luciferase reporter assays in K-562 cells we demonstrated that BQ (25 and 37microM) exposure caused an increase in c-Myb activity after 24h. Contradictory to previous findings, overexpression of exogenous c-Myb or a polypeptide consisting of c-Myb's DNA binding domain (DBD), which competitively inhibits the binding of endogenous c-Myb to DNA, did not affect Topo IIalpha promoter activity. However, BQ (37microM for 24h) exposure caused a significant increase in Topo IIalpha promoter activity, which could be blocked by the overexpression of the DBD polypeptide, suggesting that BQ exposure increases Topo IIalpha promoter activity through the c-Myb signaling pathway.
Singh
Roopam
R
Department of Pharmacology and Toxicology, Queen's University, Kingston, Ontario, Canada.
Winn
Louise M
LM
D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism*; D016227:Benzoquinones / Q000633:toxicity*; D053960:DNA Breaks / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004785:Environmental Pollutants / Q000633:toxicity; D017930:Genes, Reporter; D020570:Genes, myb / Q000187:drug effects; D006801:Humans; D020014:K562 Cells; D008156:Luciferases / Q000235:genetics; D009153:Mutagens / Q000633:toxicity; D011401:Promoter Regions, Genetic / Q000187:drug effects; D020598:Proto-Oncogene Proteins c-myb / Q000378:metabolism*; D014162:Transfection
D000951:Antigens, Neoplasm; D016227:Benzoquinones; D004268:DNA-Binding Proteins; D004785:Environmental Pollutants; D009153:Mutagens; D020598:Proto-Oncogene Proteins c-myb; C004532:quinone; D008156:Luciferases; D004250:DNA Topoisomerases, Type II