Ras stimulates DNA topoisomerase II alpha through MEK: a link between oncogenic signaling and a therapeutic target.
Topoisomerase II alpha (topo II alpha) is a major target of antitumor treatments. In an effort to determine why this protein might be a better target in tumor cells than in normal cells, we attempted to determine if the altered proliferative signaling in a tumor cell might effect the levels of expression of the topo II alpha gene. In support of this idea, it was found that topo II alpha was elevated following microinjection of oncogenic Ras protein. Oncogenic ras was further shown to stimulate the topo II alpha promoter. Stimulation by ras was independent of the normal cell cycle regulation of this promoter. Transactivation of topo II alpha by ras required both the MEK/ERK pathway, and the stress-associated protein kinase (SAPK) signaling pathway. As a direct confirmation that both ERK and SAPK were involved in topo II alpha regulation, a constitutively active MEKK that stimulates these two kinases simultaneously was shown to strongly induce topo II alpha promoter activity. Activation of either pathway alone, on the other hand, only slightly stimulated the topo II alpha promoter. Deletion analyses showed that elements near both the 5' and 3' ends of the promoter were responsible for the ras stimulation. Site-directed mutagenesis further demonstrated that an Ets-like binding site near the 5' end (-480 to -475) was one of the responsive elements. Taken together, these studies demonstrate the direct role of Ras signaling in stimulation of topo II alpha expression, and thereby establish a link between the action of a common tumor mutation and the target of multiple anti-tumor reagents.
Chen
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Department of Molecular Biology, Cleveland Clinic Foundation, OH 44195, USA.
Templeton
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D
Suttle
D P
DP
Stacey
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DW
D016475:3T3 Cells; D000818:Animals; D000906:Antibodies / Q000008:administration & dosage; D000951:Antigens, Neoplasm; D001665:Binding Sites; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D051379:Mice; D008845:Microinjections; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D050783:Proto-Oncogene Proteins c-ets; D016283:Proto-Oncogene Proteins p21(ras) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation
D000906:Antibodies; D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D014157:Transcription Factors; D017346:Protein Serine-Threonine Kinases; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; C482578:Map3k1 protein, mouse; D016283:Proto-Oncogene Proteins p21(ras); D004250:DNA Topoisomerases, Type II