DNA topoisomerase II(topII) is an essential
nuclear enzyme involved in major cellular functions such as DNA
replication transcription,rrecombination,and mitosis.While an
elevated level of topo IIa is associated with cell proliferation,
wild-type p53 inhibits the expression of various growth-stimulatory
genes. To determine if p53 downregulates topoIIa gene expression,a
murine cell line,(10)1val, that expresses a temperature-sensitive p53
was utilized.The (10)1val cells had significantly lower level of topo
IIa mRNA and protein following incubation for 24 h at 32C(p53 with wt
conformation) than at 39C(p53 with mutant conformation).The effect of
p53 on the human topo IIa gene promoter was determined by using
luuciferase reporter plasmids containing varying lengths of the
topoIIa promoter transiently cotransfected into p53-deficient (10)1
cells together with wt or mutant p53 expression
plasmids.Transcription from the full-length bp-557 to +90) topo IIa
promoter was decreased 15-fold by wt p53 in a
concentration-dependent manner.wheras mutant p53 exerted much weaker
inhibition.Consecutive deletion of the five inverted CCAAT
elements(ICEs) from the topo IIa promoter reduced both the basal
promoter activity and wt p53-induced supression.Transcription of the
minimal promoter (-32 to +90),which contains no ICE,was slightly
stimulated by wt or mutant p53 expression.When point mutations were
introduced into the most proximal ICE (-68),the inhibitory effect of
wt p53 was alleviated and stimulation of topoIIa expression
resulted.Our study suggests interation with specific
ICEs.Inactivation of wt wt p53 may reduced normal regulatory
supression of topo IIa and contribute to abortive cell cycle
checkpoints,accelerated cell proliferation,and alterations in genomic
stability associated with neoplasia.
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