| Summary: | 碩士 === 國立臺灣大學 === 生化科學研究所 === 99 === Chaperonin containing t-complex polypeptide 1 subunit β (CCT-β) is a molecular chaperone that facilitates protein folding in eukaryotic cytosol, and the expression is elevated in a variety of drug-resistant tumor types (Lin et al., 2009). In this thesis, I first identified the expression of CCT-β was up-regulated in two drug-resistant cancer cells compared to their parental cancer cells. Besides, transfecting CCT-β in cancer cells increased the resistance to paclitaxel. In contrast, transient knockdown of CCT-β by siRNA restored the sensitivity to paclitaxel in drug-resistant cancer cells. Furthermore, promoter analysis revealed that Sp1 and Elk1 are critical for activation of the CCT-β promoter, which were reported deregulation in cancer cells and related with cancer initiation or progression. After mutating these transcription factor binding sites, luciferase reporter assay using MES-SA/Dx-5 and 7-TR showed down-regulated expression, demonstrating that transcription of the gene encoding the β subunit of CCT is regulated by Sp1 and Elk1 in drug-resistant cancer cells. Moreover, previous studies have reported phosphorylation of Elk1 increased DNA-binding ability and promoted the transcription of specific genes. Elk1 has been proved to be a substrate of MAPK. There are three subfamily of MAPK: ERK, JNK, and p38. Treatment of different inhibitors, respectively, revealed that only inhibition of the p38 signaling pathway by SB 203580 was sufficient to reduce phosphorylation of Elk1, further affecting the expression of CCT-β in time- or dose-dependent manner. Otherwise, MDR1, which is thought to be the major reason for drug resistance, was also down-regulated by inhibition of p38 pathway. Therefore, blocking p38 pathway not only down-regulates the expression of CCT-β but also MDR1.
Overall, these studies elucidate the possible mechanisms underlying the up-regulation of CCT-β in drug-resistant cancer cells, transcription of the CCT-β regulated by phosphorylation of Elk1 under the control of p38 signaling pathway, and simultaneous regulation of MDR1 expression. More studies are needed to find out an unknown factor that induces this pathway to mediate the transcription of CCT-β and MDR1, and the correlation between CCT-β and MDR1. These may serve as the therapeutic targets to develop drugs for treating multidrug-resistant cancers.
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