DNA topoisomerase
II alpha

EC Number: EC 5.99.1.3.
TOP2A (gene locus)

Gene: TOP2A maps to 17q21-q22, close to ERBB2.
mRNA: size: kb
Protein: DNA topoisomerases are enzymes that control and alter the topologic states of DNA in both prokaryotes and eukaryotes. Topoisomerase II from eukaryotic cells catalyzes the relaxation of supercoiled DNA molecules, catenation, decatenation, knotting and unknotting of circular DNA (Watt P.M. and Hickson I.D., 1994). It appears likely that the reaction catalyzed by topoisomerase II involves the crossingover of 2 DNA segments. Topoisomerase II has been correlated with the proliferative state of cells (Heck M.M. and Earnshaw W.C., 1986).

Cell lines:
- MCF-7 BCC selected in Adriamycin in the presence of verapamil developed a multidrug resistant phenotype, which was characterized by as much as 100,000-fold resistance to mitoxantrone, 667-fold resistance to daunorubicin, and 600-fold resistance to doxorubicin. Immunoblot and PCR analyses demonstrated no increase in MDR-1 or MRP expression in resistant cells, relative to parental cells. This phenotype is similar to one previously described in mitoxantrone-selected cells. The cells, designated MCF-7 AdVp, displayed a slower growth rate without alteration in topoisomerase II alpha level or activity (Lee J.S. et al., 1997).

- In MCF-7 BCC transfected with c-erb-B2 showed markedly increased sensitivity to doxorubicin and etoposide. Topo II alpha mRNA and protein (total protein and enzymatic decatenating activity) were found to be up-regulated in c-erb-B2-transfected cells. Moreover, topo II alpha promoter activity was also modestly increased in c-erb-B2-transfected cells. Because up-regulation of topo II alpha in vitro and in clinical specimens is associated with increased response to doxorubicin (presumptively by an increase in drug substrate), this may be the mechanism of the increased sensitivity to doxorubicin seen in c-erb-B2-transfected cells (Harris L.N. et al., 1998).

- Reduced expression of topoisomerase II alpha in tumors has been implicated as a mechanism of resistance of tumor cells to topoisomerase II alpha inhibitors such as doxorubicin, m-amsacrine, and the epipodophyllotoxins. However, in a study of 11 MCF-7, ZR-75-B, or T-47D sublines selected on the basis of their resistance to doxorubicin, only 2 sublines were found to express a lower topoisomerase II alpha mRNA level (Wosikowski K. et al., 1997).

Tumors:
- In a study of 50 breast tumors, the topoisomerase II alpha locus was co-amplified in 3 cases out of 6 with erbB2 amplification (Keith W.N. et al., 1993).

- In 117 primary breast cancers, 25 were found to be amplified for erbB2. Three of these cases showed co-amplification of topo II alpha. Topo II beta was not amplified (Smith K. et al., 1993).
- Cryostat sections from 63 primary invasive ductal breast carcinomas were stained immunohistochemically for topoisomerase II-alpha. Topoisomerase II-alpha nuclear immunoreactivity (median 14% of nuclei; range 2-62%) was detected in all tumours with highly variable intertumour and intratumour nuclear reactivity. Higher levels of topoisomerase II-alpha expression were strongly related to higher tumour grade, larger tumour size, nodal status, and the presence of distant metastases at diagnosis. No correlation was found with menopausal status, steroid hormone receptor status, disease free survival, or overall survival (Hellemans P. et al., 1995).

- In a series of 56 primary breast tumour samples, there was no relationship between any of the commonly used pathological variables [tumour size, lymph node status, S-phase fraction (SPF)] and the level of expression of topoisomerase II beta mRNA. However, high topoisomerase II alpha gene expression was significantly associated with a high SPF (sign-rank test; P = 0.01). Moreover, the ratio of mRNA levels for topoisomerase II alpha and beta showed a stronger relationship to SPF (median raito 0.62 for tumours with SPF < 10, and 1.64 for SPF > 10; P = 0.0021, sign-rank test). As expected from previous studies, an SPF > 10 was associated with poor overall survival (P = 0.01). Immunohistochemical analysis revealed that topoisomerase II beta was widely distributed ( > 90% positive tumour cells), but that topoisomerase II alpha expression was less widely expressed, with a pattern of expression similar to that of the proliferation-dependent antigen recognised by Ki67 (Sandri M.I. et al., 1996).

- In a immunohistochemical study of 356 paraffin-embedded node-negative infiltrating ductal carcinomas (the patients were followed for a median duration of 99 months), both p53 and c-erbB-2 were significantly associated with high tumour grade, large tumour size, DNA aneuploidy, lack of steroid hormone receptors, young age, and increased topoisomerase II alpha and Ki-67 expression levels. Topoisomerase II alpha and Ki-67 scores closely paralleled each other, indicating that both reflect the proliferative activity of tumour cells. A univariate analysis of overall (OS), specific (SS), and disease-free survival (DFS) revealed all the above-mentioned parameters to be statistically significant except patient age, which was relevant only to overall survival. Multivariate analysis with inclusion of all covariates selected tumour size and proliferation (topoisomerase II alpha and Ki-67) indices as independent predictors of survival (Rudolph P. et al., 1999).

- Topo II alpha was studied by immunohistochemistry in formalin-fixed, paraffin-embedded primary breast cancers from 184 women (mean age, 60 years). On univariate analysis, increased topo II expression correlated with decreased patient survival, advanced tumor stage, lymph node metastasis, and HER-2 amplification. Topo II expression did not correlate with tumor size, grade, estrogen receptor/progesterone receptor status, or disease recurrence. On multivariate analysis, stage, lymph node metastasis, and tumor grade all independently predicted disease-related death (Depowski P.L. et al., 2000).

Depowski P.L. et al. (2000) Topoisomerase IIalpha expression in breast cancer: correlation with outcome variables. Mod. Pathol. 13, 542-547.
Harris L.N. et al. (1998) Induction of sensitivity to doxorubicin and etoposide by transfection of MCF-7 breast cancer cells with heregulin beta-2. Clin. Cancer Res. 4, 1005-1012.
Heck M.M. and Earnshaw W.C. (1986) Topoisomerase II: a specific marker for cell proliferation. J. Cell Biol. 103, 2569-2581.
Hellemans P. et al. (1995) Immunohistochemical study of topoisomerase II-alpha expression in primary ductal carcinoma of the breast. J. Clin. Pathol. 48, 147-150.
Keith W.N. et al. (1993) Co-amplification of erbB2, topoisomerase II alpha and retinoic acid receptor alpha genes in breast cancer and allelic loss at topoisomerase I on chromosome 20. Eur. J. Cancer 29A, 1469-1475.
Lee J.S. et al. (1997) Reduced drug accumulation and multidrug resistance in human breast cancer cells without associated P-glycoprotein or MRP overexpression. J. Cell. Biochem. 65, 513-526.
Sandri M.I. et al. (1996) Differential expression of the topoisomerase II alpha and beta genes in human breast cancers. Br. J. Cancer 73, 1518-1524.
Smith K. et al. (1993) Topoisomerase II alpha co-amplification with erbB2 in human primary breast cancer and breast cancer cell lines: relationship to m-AMSA and mitoxantrone sensitivity. Oncogene 8, 933-938.
Tsai-Pflugfelder M. et al. (1988) Cloning and sequencing of cDNA encoding human DNA topoisomerase II and localization of the gene to chromosome region 17q21-22. Proc. Natl. Acad. Sci. USA 85, 7177-7181.
Tan K.B. et al. (1992) Topoisomerase II-alpha and topoisomerase II-beta genes: characterization and mapping to human chromosomes 17 and 3, respectively. Cancer Res. 52, 231-234.
Keith W.N. et al. (1992) Amplification of the topoisomeraseII alpha gene in a non-small cell lung cancer cell line and characterisation of polymorphisms at the human topoisomerase II alpha and beta lociin normal tissue. Genes Chromosomes Cancer 4, 169-175.
Rudolph P. et al. (1999) Correlation between p53, c-erbB-2, and topoisomerase II alpha expression, DNA ploidy, hormonal receptor status and proliferation in 356 node-negative breast carcinomas: prognostic implications. J. Pathol. 187, 207-216.
Watt P.M. and Hickson I.D. (1994) Structure and function of type II DNA topoisomerases. Biochem. J. 303, 681-695 (Review).
Wosikowski K. et al. (1997) Altered gene expression in drug-resistant human breast cancer cells. Clin. Cancer Res. 3, 2405-2414.

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