c-Myb trans-activates the human DNA topoisomerase IIalpha gene promoter.
DNA topoisomerase IIalpha (topo IIalpha) is an essential proliferation-dependent nuclear enzyme which has been exploited as an anti-tumor drug target. Since the proliferative status of human leukemia cells is associated with expression of the c-myb proto-oncogene, c-Myb was investigated as a trans-activator of the topo IIalpha gene. Using topo IIalpha promoter-luciferase reporter plasmids, c-myb expression caused trans-activation of the topo IIalpha promoter a maximum of approximately 4.5-fold over basal levels in HL-60 human promyelocytic leukemia cells. Trans-activation was submaximal with higher levels of c-myb expression plasmid but a Myb protein lacking its negative regulatory domain resulted in approximately 19-fold trans-activation. Mutagenesis and 5'-deletion studies revealed that Myb trans-activation was mediated via a Myb-binding site at positions -16 to -11 and that this region governed the bulk of basal topo IIalpha promoter activity in human leukemia cells. Trans-activation of topo IIalpha by c-Myb was lymphoid- or myeloid-dependent. However, B-Myb, a more widely-expressed Myb family member, caused topo IIalpha trans-activation in both HL-60 cells and HeLa epithelial cervical carcinoma cells. These data provide evidence for a new Myb-responsive gene which is directly linked to and required for cellular proliferation.
Brandt
T L
TL
Department of Pharmaceutical Sciences, University of Colorado School of Pharmacy and the University of Colorado Cancer Center, Denver, Colorado 80262, USA.
Fraser
D J
DJ
Leal
S
S
Halandras
P M
PM
Kroll
A R
AR
Kroll
D J
DJ
D002455:Cell Division; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D011401:Promoter Regions, Genetic; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D020598:Proto-Oncogene Proteins c-myb; D017384:Sequence Deletion; D015534:Trans-Activators / Q000502:physiology*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D015534:Trans-Activators; D004250:DNA Topoisomerases, Type II