Abstract

BACKGROUND: Breast cancer is a complex, heterogeneous disease and one of the most common malignancies in women worldwide. The efficacy of chemotherapy as an important breast cancer treatment option has been severely limited because of the inherent or acquired resistance of cancer cells. The molecular chaperone heat shock protein 90 (HSP90) upregulated in response to cellular stress is required for functions such as conformational maturation, activation and stability in more than 200 client proteins, mostly of the signaling type. In this study, the expression of HSP90 isoforms including HSP90alpha and HSP90beta in breast cancer cell lines before and after treatment with doxorubicin (DOX) was assessed. MATERIAL AND METHODS: The cell cytotoxicity of DOX in MDA-MB-231 and MCF-7 cell lines was determined using the MTT assay. Immunofluorescence and western blotting techniques were used to determine the expression of HSP90beta in the cell lines before and after DOX treatment. Immunofluorescence was also conducted to ascertain the expression of HSP90alpha. RESULTS: The MTT assay results showed that the MDA-MB- 231 cells (IC(50)=14.521 muM) were more sensitive than the MCF-7 cells (IC(50)=16.3315 muM) to DOX. The immunofluorescence results indicated that the expression of HSP90alpha in both cell lines decreased after exposure to DOX. The western blot and immunofluorescence analyses showed that HSP90beta expression decreased in the MCF-7 cells but increased in the MDA-MB- 231 cells after DOX treatment. Conclusion: The obtained results suggested that HSP90alpha and HSP90beta expression levels were reduced in the MCF-7 cells after exposure to DOX. In the MDA-MB-231 cells, HSP90alpha expression was reduced while HSP90beta was found to be overexpressed following DOX treatment.