TOPOISOMERASE II EXPRESSION IN DRUG RESISTANCE

II型DNA拓扑异构酶（topII）是一种必需的酶，也是 细胞内靶向的临床最有效的 间谍。 细胞内的top II是一个重要的 细胞对top II靶向敏感性的决定因素 药物和减少top II表达是最常见的观察到的顶部 II介导的耐药性。 在两种最高II亚型中，170 kD 形式（top II alpha）是介导top II功能的主要形式 对II类靶向药物高度敏感。 转染和 通过负反馈机制过度表达Top II α基因， 对于严格调节细胞顶II α水平是重要的 也可能有助于降低药物中的top II α表达， 阻力 此外，一个顺式元件及其各自的结合 在中国仓鼠顶部II α启动子中鉴定了活性， 它与c-erbB 2中的一种新的抑制元件相似， 启动子 top II α和c-erbB 2的扩增和过表达 基因与乳腺癌的不良预后有关。 因此，我们认为， 对top II alpha调节机制的研究 显著的生物学和临床相关性。 在这个提议中，控制自动调节的分子机制 在过表达CHO的EMT 6细胞中内源性top II alpha表达的 top II α和两种耐药细胞中top II α表达降低， 将对中国仓鼠细胞系进行研究和比较。 的 研究结果将被用于研究如何调节顶II α， 在耐药细胞系中的表达和药物敏感性 将对细胞进行分析。 基于CHO和人之间的高度同源性， II α启动子和保守的调控元件， 因素，这项研究的结果是相关的研究顶端II 在人类癌症中的表达，并制定克服 II类介导的癌症化疗耐药性。 阐明 调节tip II α表达的机制也很重要， 研究top II在不同细胞功能中的作用。

Type II DNA topoisomerase (topII) is an essential enzyme and is also the intracellular target for the number of clinically most effective antineoplastic agents. The intracellular level of top II is an import determining factor for the cellular sensitivity to top II-targeting drugs and reduced top II expression is the most commonly observed top II-mediated drug resistance. Of the two top II isoforms, the 170 kD form (top IIalpha) is the predominant form to mediate top II functions and is highly sensitive to top II-targeting agents. Transfection and overexpression of top IIalpha gene by negative feedback mechanism, which is important for a strict regulation of the cellular top IIalpha level and may also contribute to reduced top IIalpha expression in drug resistance. In addition, one cis-element and its respective binding activity was identified in the Chinese hamster top IIalpha promoter and it bears resemblance to a novel inhibitory element in the c-erbB2 promoter. Amplification and overexpression of top IIalpha and c-erbB2 genes have been associated with poor prognosis in breast cancer. Hence, the study of mechanisms by which top IIalpha is regulated has significant biological and clinical relevance. In this proposal, the molecular mechanisms governing the autoregulation of endogenous top IIalpha expression in EMT6 cells that overexpress CHO top IIalpha and the reduced top IIalpha expression in two drug resistant Chinese hamster cell lines will be investigated and compared. The results will then be used in the study of modulating the top IIalpha expression in the resistant cell lines and the drug sensitivity of the cells will be assayed. Based on the high homology between CHO and human to IIalpha promoters and the conserved regulatory elements and binding factors, the results of this study are relevant for the study of top II expression in human cancer and for developing strategies in overcoming top II-mediated drug resistance in cancer chemotherapy. Elucidating the mechanisms of regulating tip Iialpha expression is also important in studying the roles of top II in different cell functions.