Mechanisms of Paclitaxel-Induced Apoptosis in an Ovarian Cancer Cell Line and Its Paclitaxel-Resistant Clone

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Abstract
Background: To understand the complicated network of paclitaxel (PTX)-induced apoptosis pathways and to elucidate mechanisms of drug resistance in ovarian cancer, we looked at PTX-induced apoptosis by using cDNA microarray. We also quantitated the changes in apoptosis-related proteins in the process of apoptosis. Methods: An ovarian cancer cell line KF, and its PTX-resistant clone KFTX, were treated with PTX or carboplatin (CBDCA). After exposure to PTX or CBDCA, the induction of apoptosis was examined by internucleosomal DNA fragmentation. Changes in mRNA expression after 12 h of exposure to PTX were studied using cDNA microarray and RT-PCR. Changes in P53 and Bcl-2 levels were also measured over 24 h by ELISA. Results: With increased doses of PTX or CBDCA, an increase in apoptosis was noted in both cell lines. cDNA microarray revealed that PTX treatment upregulated expression of caspase 1, 2, 3, 4, 6, 9, 10, their activator apaf-1, and stress reaction-related genes, gadd34, gadd153 in KF, although most of them were unchanged or downregulated in KFTX. bag-1 and hsc70 were markedly upregulated in KFTX. p53 and bcl-2 were not upregulated in either cell line. Results from protein studies also supported the cDNA microarray data. Conclusion:p53-independent mitochondrial pathways and stress-reaction-induced pathways play critical roles in PTX-induced apoptosis in ovarian cancer cells. Suppression of those pathways and upregulation of bag-1 and hsp-70 played an important role in acquiring resistance to PTX.