Elevated expression of DNA topoisomerase II in camptothecin-resistant human tumor cell lines

Yoshikazu Sugimoto, Satomi Tsukahara, Tomoko Oh-hara, Leroy F. Liu, Takashi Tsuruo

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133 Citations (Scopus)


In a previous study, we established camptothecin (CPT)-resistant cell lines, A549/CPT and HT-29/CPT, from human lung cancer A549 and human colon cancer HT-29. A549/CPT was shown to express similar amounts of DNA topoisomerase I (topo I) as the parental line, and HT-29/CPT was shown to express lower amounts of topo I than its parental line. DNA topoisomerases I and II are known to be functionally related. In the present study, the possible alterations in topo II expression were examined in these human CPT-resistant lines. In A549/CPT and HT-29/ CPT, the cellular contents of topo II and its mRNA were elevated over that seen in each parental line. Nuclear extracts from A549/CPT and HT-29/CPT showed higher topo II activity than those from the corresponding parental lines when the same amounts of nuclear protein were used. Topo II was partially purified from HT-29 and HT-29/CPT by hydroxylapatite column chromatography, and the enzyme activities were compared. HT-29/CPT showed higher topo II activity in the hydroxylapatite column-eluted fractions than HT-29. These results indicate the possible activation of topo II expression in the CPT-resistant cell lines.

Original languageEnglish
Pages (from-to)7962-7965
Number of pages4
JournalCancer Research
Issue number24
Publication statusPublished - Dec 15 1990
Externally publishedYes

ASJC Scopus subject areas

  • Cancer Research
  • Oncology


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