| Summary: | 碩士 === 國立嘉義大學 === 生化科技學系研究所 === 98 === Lung cancer is one of the most common malignant tumor in the world. Erlotinib (Tarceva®) is a selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor in the treatment of human non-small cell lung cancer (NSCLC). Emodin, acting like a tyrosine kinase inhibitor, is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants. Emodin exhibits anticancer effects against a variety of cancer cells, including lung cancer cells. Rad51 and ERCC1proteins are essential for homologous recombination repair (HRR) and nucleotide excision repair (NER), respectively for DNA damage. In addition, overexpression of Rad51 or ERCC1 is associated with resistance to chemotherapy in tumor cells and correlates with poor prognosis. In this thesis, we investigated the roles of ERK1/2 and AKT signaling pathways in regulating Rad51 and ERCC1 expression and cytotoxic effects induced by erlotinib or emodin in different NSCLC cell lines. These results demonstrate that erlotinib decreased cellular levels of phospho-ERK1/2, phospho-AKT, Rad51 protein and mRNA in erlotinib-sensitive H1650 and A549 cells, leading to cell death via apoptosis, and enhanced Rad51 mRNA and protein instability, but these results were not seen in erlotinib-resistant H520 and H1703 cells. Interestingly, both ERCC1 and Rad51 protein levels as well as mRNA levels were decreased in four different NSCLC cell lines after exposure to emodin. Moreover, knocking down endogenous Rad51 expression by si-Rad51 RNA transfection significantly enhanced erlotinib- or emodin-induced cytotoxicity. Moreover, transient transfection of human NSCLC cells with si-ERCC1 RNA or cotreatment with U0126 could enhance emodin-induced cytotoxicity. Therefore, the MKK1/2-ERK1/2 pathway is the upstream signal to maintain the expressions of ERCC1 and Rad51, which are suppressed by emodin to induce cytotoxicity in NSCLC cells. Finally, blocking the activations of ERK1/2 and AKT by MKK1/2 inhibitor (U0126) and phosphatidyl-inositol 3-kinase (PI3K) inhibitor (wortmannin) suppress the expression of Rad51 and enhance the erlotinib-induced cell death in erlotinib-resistant cells. In conclusion, these results demonstrate that suppression of Rad51 or ERCC1 may be a novel therapeutic modality in overcoming drug resistance of erlotinib in human NSCLC in the future.
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