Abstract
Topoisomerase IIα (170 kDa) expressed in human HL-60 cells is heterogeneous in charge. By two-dimensional electrophoresis and chromatofocussing two major subforms with pi of 6.5 and 6.7 can be resolved. By preparative anion-exchange chromatography we separated the known topoisomerase II isoenzymes (170/180 kDa) and in addition a late-eluting 170 kDa form, which has not been described before. The catalytic optimum of this late-eluting form is shifted to pH 9.4. It is more than 100-fold resistant to orthovanadate, amsacrine or etoposide, and has an increased salt stability. SDS-treatment induces covalent attachment of this enzyme fraction to calf thymus DNA in the absence of drug. The latter observations indicate an increase in DNA-binding. In the tightly DNA-bound state the late-eluting enzyme is not targeted by cleavable complex forming drugs. Accordingly, cells may become drug-resistant by expressing this form predominantly.
| Original language | English |
|---|---|
| Journal | Acta Oncologica |
| Volume | 33 |
| Issue number | 7 |
| Pages (from-to) | 799-806 |
| Number of pages | 8 |
| ISSN | 0284-186X |
| DOIs | |
| Publication status | Published - 1994 |
Funding
We would like to thank Dr. Frank Cieseler for making available to us the resistant cell line HL-60/R. characterized in his laboratory. Excellent technical assistance by Michaela Miiller and Michael Clark is gratefully acknowledged. This work was sup- ported by Wilhelm Sander-Stiftung, grant No. 90.038.02 and Deutsche Forschungsgemeinschaft, SFB 172, C9.
