Evidence for repressional role of an inverted CCAAT box in cell cycle-dependent transcription of the human DNA topoisomerase IIalpha gene.
Expression of DNA topoisomerase IIalpha (topo IIalpha) is cell cycle-regulated at both the transcriptional and the post-transcriptional levels. In order to identify cis-acting elements responsible for transcriptional regulation during the cell cycle, we investigated NIH/3T3 cells stably transfected with luciferase reporter plasmids containing various lengths of the human topo IIalpha gene promoter. Serum-deprived cells expressed low levels of luciferase, and following serum-induced cell cycle re-entry luciferase levels were gradually elevated 2-fold. During S phase, a steep 3-fold increase in luciferase activity was seen, reaching its maximum approximately 22 h after serum addition. This pattern was observed with both a full-length (nucleotides (nt) -295 to +90] and a deletion (nt -90 to +90) promoter construct. In contrast, when testing a deletion construct (nt -51 to +90) lacking the first inverted CCAAT box (ICB1) the S phase-specific induction was absent. Mutation of ICB1 revealed that it had a repressive character, since luciferase levels rose rapidly to maximal levels immediately following serum addition. Furthermore, electrophoretic mobility shift assays demonstrated a marked decrease in ICB1 binding activity following serum addition. Together, this suggests a role of ICB1 in cell cycle-dependent repression of topo IIalpha transcription.
Falck
J
J
Department of Pathology, Laboratory Center, Rigshospitalet, DK-2100 Copenhagen, Denmark.
Jensen
P B
PB
Sehested
M
M
D016475:3T3 Cells; D000818:Animals; D000951:Antigens, Neoplasm; D022762:CCAAT-Enhancer-Binding Proteins; D002453:Cell Cycle; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000235:genetics*; D051379:Mice; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism*; D016196:S Phase; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
D000951:Antigens, Neoplasm; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D012097:Repressor Proteins; D014157:Transcription Factors; D004250:DNA Topoisomerases, Type II