TOPOISOMERASE II EXPRESSION IN DRUG RESISTANCE

II型DNA拓扑异构酶(TopII)是一种必需的酶，也是 临床上最有效的细胞内靶点数目 抗肿瘤药物。TOP II的细胞内水平是一种重要的 细胞对TOP II靶向敏感性的决定因素 药物和TOP II表达减少是最常观察到的TOP II-介导的耐药性。在两个顶级II亚型中，170 kD 形式(Top IIpha)是调节top II功能的主要形式 并且对顶级II靶向制剂高度敏感。转染法和 通过负反馈机制过表达top IIpha基因， 对于严格调节细胞顶级IIAlpha水平很重要 也可能有助于减少药物中Top IIpha的表达 抵抗。此外，一个顺式元件及其各自的结合 在中国仓鼠TOP IIAlpha启动子和 它与c-erbB2中的一种新的抑制元件相似。 推动者。TOPⅡα和c-erbB2基因的扩增和过表达 基因与乳腺癌预后不良有关。因此， 对TOP IIAlpha调控机制的研究已经 显著的生物学和临床相关性。 在这一建议中，控制自动调节的分子机制 过表达CHO的EMT6细胞内源性TOP IIpha的表达 两种药物耐药患者的Top IIpha及其表达降低 将对中国仓鼠细胞系进行调查和比较。这个 然后，结果将用于调制TOP IIAlpha的研究 耐药细胞株中的表达及其对药物的敏感性 将对细胞进行化验。基于CHO与人类的高度同源性 到IIpha启动子和保守的调控元件及结合 因素，本研究的结果对TOP II的研究是相关的 在人类癌症中的表达及其克服策略的发展 TOP II介导的肿瘤化疗耐药。澄清 调节TIP Iipha表达的机制也是重要的 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.