Effects of wild-type p53 expression on the quantity and activity of topoisomerase IIα and β in various human cancer cell lines

✍ Scribed by Daniel Hochhauser; Nikola I. Valkov; Jana L. Gump; Irene Wei; Carolyn O'Hare; John Hartley; Jianguo Fan; Joseph R. Bertino; Debabrata Banerjee; Daniel M. Sullivan

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 455 KB
• Volume: 75
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/(sici)1097-4644(19991101)75:2<245::aid-jcb7>3.0.co;2-g

✦ Synopsis

The p53 null HL-60 cell line was transfected with plasmids coding for either the wild-type p53 or mutant p53 gene. The stable expression of wild-type p53 resulted in a significant increase in sensitivity to the topoisomerase II poisons etoposide and doxorubicin, but not to the topoisomerase II inhibitors razoxane and ADR-529. HL-60 cells expressing wild-type p53 demonstrated 8-to 10-fold more VP-16 induced DNA breaks by the alkaline elution assay. The effect of inducible expression of wild-type p53 was also studied in the p53 null erythroblastoid cell line K562 and in the human squamous carcinoma cell line SqCC. The inducible expression of wild-type p53 in the K562 cell line resulted in a 3-fold increase in sensitivity to VP-16. The quantity of topoisomerase II␣ was not altered by the transfection as determined by immunoblotting, while the amount of the ␤ isoform was increased 2.5-fold in HL-60 cells. The topo II catalytic activity present in nuclear extracts was measured as the decatenation of kinetoplast DNA, and found to be unaltered by p53 expression. Immunostaining for topoisomerase II␣ was substantially diminished in both stable and inducible wild-type p53 expressing cells when three different antibodies were used (two polyclonal and one monoclonal). However, the addition of VP-16 resulted in a rapid appearance of nuclear fluorescence for topoisomerase II␣. No changes in topoisomerase II␤ immunostaining were observed. These results suggest that an epitope for topoisomerase II␣ is concealed in cells expressing wild-type p53 and that a complex between topoisomerase II␣ and p53 may be disrupted by the addition of antitumor drugs.