The topoisomerase II–Hsp90 complex: A new chemotherapeutic target?

Abstract

The modulation of DNA topology by topoisomerase II plays a crucial role during chromosome condensation and segregation in mitosis and has thus become a highly attractive target for chemotherapeutic drugs. However, these drugs are highly toxic, and so new approaches are required. One such strategy is to target topoisomerase II-interacting proteins. Here we report the identification of potential topoisomerase II-associated proteins using immunoprecipitation, followed by 1-D and 2-D gel electrophoresis and MALDI-TOF mass spectrometry. A total of 23 proteins were identified and, of these, 17 were further validated as topoisomerase IIa-associated proteins by coimmunoprecipitation and Western blot. Six of the interacting proteins were cellular chaperones, including 3 members of the heat shock protein-90 (Hsp90) family, and so the effect of Hsp90 modulation on the antitumor activity of topoisomerase II drugs was tested using the sulforhodamine B assay, clonogenic assays and a xenograft model. The Hsp90 inhibitors geldanamycin, 17-AAG (17-allylamino-17-demethoxygeldanamycin) and radicicol significantly enhanced the activity of the topoisomerase II poisons etoposide and mitoxantrone in vitro and in vivo. Thus, our method of identifying topoisomerase II-interacting proteins appears to be effective, and at least 1 novel topoisomerase IIa-associated protein, Hsp90, may represent a valid drug target in the context of topoisomerase II-directed chemotherapy. ' 2005 Wiley-Liss, Inc.Key words: topoisomerase II; Hsp90; protein-protein interactions; chemotherapy Topoisomerase II is an essential nuclear enzyme that modulates DNA topology by generating double stranded breaks, allowing the passage of 1 double strand of DNA through another via an ATPdependent mechanism.1,2 This enzyme is a component of DNA transcription and replication machinery, required for chromosomal segregation and maintenance of the nuclear scaffold.2 Recently, topoisomerase II has also been shown to be required for RNA polymerase II transcription.3 In humans, 2 topoisomerase II isoforms have been identified, topoisomerase IIa 4 and b. 5 The 2 isoforms differ in their cell cycle expression, nuclear localization and tissue specific expression. 6 As type II topoisomerases play such an important role within dividing cells, they are highly attractive targets for chemotherapeutic agents, especially in human cancers.Topoisomerase II can be inhibited via one of two mechanisms: Topoisomerase II poisons act by enhancing DNA cleavage and inhibiting DNA ligation, thus increasing the level of stabilized enzyme-DNA cleavage intermediate complexes. Poisons take advantage of the catalytic mechanism by changing the enzymatic conformation and converting it to a cellular toxin.7 Examples are etoposide (VP16) and mitoxantrone. Catalytic inhibitors, however, target other stages of the topoisomerase II catalytic cycle. The bisdioxopiperazines, e.g. ICRF-159, ''lock'' the ATP-operated clamp of the enzyme, causing death by deprivation of the essential activity of topoisomerase II rath...

miR-181a and miR-630 Regulate Cisplatin-Induced Cancer Cell Death

“…3). The profiles of miRNAmediated cell death sensitization/protection that were most closely related to each other were those of etoposide and mitoxantrone, in line with the notion that these compounds (at least partially) operate as topoisomerase II inhibitors (30,31). Altogether, these results indicate that miRNAs can affect the apoptotic response of the same cell type to different cell death inducer in a stimulus-dependent fashion.…”

Inhibition of p38 MAPK-Dependent Excision Repair Cross-Complementing 1 Expression Decreases the DNA Repair Capacity to Sensitize Lung Cancer Cells to Etoposide

“…In addition, 17-AAG significantly enhanced the activity of etoposide in human colon cancer HCT116 cells (21). Thus, we proposed that 17-AAG could enhance etoposide-induced cytotoxic effect through the downregulation of p38 MAPK-mediated ERCC1 expression in NSCLC cells.…”

“…17-AAG significantly enhances the activity of etoposide in human colon cancer HCT116 cells (21). The molecular mechanism of 17-AAG enhancement of the etoposideinduced cytotoxic effect through modulation of p38 MAPK signaling in NSCLC has yet to be defined.…”

Ratio of proliferation markers and HSP90 gene expression as a predictor of pathological complete response in breast cancer neoadjuvant chemotherapy

“…Nevertheless, also in triple negative patients or luminal B subtype there was also a trend for worse prognosis related to higher HSP90 expression. TOPO2-HSP90 complex has also been indicated by Barker et al as a potential valuable chemotherapeutic target [30].…”