Anticancer Drug Resistance by Bcl-2 Oncogene Expression

描述(申请人提供)：本研究项目的目标一直是，并将继续确定肿瘤细胞对癌症化疗药物耐药的机制。BCL-2是一个蛋白质家族的原型成员，其主要功能似乎是调节细胞凋亡。BCL-2在多种人类肿瘤中高表达，并通过阻断肿瘤进展过程中的细胞凋亡为肿瘤提供生长优势。然而，这种阻断也使这些肿瘤细胞对抗癌治疗产生抗药性，包括大多数依赖于细胞凋亡作为主要细胞杀伤模式的癌症化疗药物。事实上，Bcl-2的表达产生了多药耐药(MDR)表型。目前尚不清楚Bcl2调控细胞凋亡的机制。我们先前已经证明，表达Bcl-2的细胞内有更高水平的谷胱甘肽(GSH)。正如我们在这一应用中所证明的那样，表达Bcl-2的细胞的线粒体也具有更高的GSH水平，并增强了将GSH从胞浆主动运输到线粒体的能力。这些新发现与Bcl2抑制线粒体细胞凋亡的能力完全一致，我们认为Bcl2表达引起的多药耐药可以通过抑制或逆转Bcl2‘S对线粒体谷胱甘肽水平的上调而逆转。因此，在这一应用中，特定的目标1和2旨在表征Bcl-2对线粒体GSH转运的影响，并验证线粒体GSH水平直接调节线粒体凋亡的假说。在目标3中，我们建议对一种新的线索进行跟踪，并研究在细胞接收到凋亡信号后，Bcl-2蛋白是否重新分布到质膜上。最后，在特定的目标4中，我们建议通过使用能够使GSH从细胞或线粒体外流的药物来研究克服Bcl2介导的多药耐药的策略。这个项目的意义与癌症治疗中的多药耐药问题有关。我们的中心假设是，了解Bcl2‘S阻断抗癌药物诱导的细胞凋亡的生化和分子基础将有助于制定逆转这种耐药性和提高治疗效果的策略。

DESCRIPTION (provided by applicant): The goal of this research project has been and remains to define the mechanism responsible for the resistance of tumor cells with abnormal expression of the Bcl-2 oncogene to cancer chemotherapy agents. Bcl-2 is the prototypic member of a family of proteins, whose main function appears to be the regulation of apoptosis. Bcl-2 is highly expressed in a variety of human cancers and provides a growth advantage to tumors by blocking apoptosis during tumor progression. However, this block also renders such tumor cells resistant to anticancer therapies including most cancer chemotherapy drugs that rely on apoptosis as their primary mode of cell killing. Indeed, Bcl-2 expression produces a multi-drug resistance (MDR) phenotype. The mechanism by which Bcl-2 regulates apoptosis is not understood. We have previously shown that Bcl-2 expressing cells have higher intracellular levels of glutathione (GSH). As we demonstrate in this application, the mitochondria from Bcl-2 expressing cells also have higher GSH levels and have enhanced capacity to actively transport GSH from the cytosol into mitochondria. These are novel findings that are entirely consistent with the ability of Bcl-2 to suppress mitochondrial apoptosis; it is our contention that MDR due to Bcl-2 expression could be reversed by inhibiting or reversing Bcl-2's enhancement of mitochondrial GSH levels. Therefore, in this application, Specific Aims 1 and 2 are directed at characterizing this effect of Bcl-2 on mitochondrial GSH transport and testing the hypothesis that the level of mitochondrial GSH directly regulates mitochondrial apoptosis. In Aim 3, we propose to follow up on a new lead and investigate whether Bcl-2 protein is redistributed to the plasma membrane after cells receive an apoptotic signal. Finally, we propose in Specific Aim 4 to investigate strategies for overcoming Bcl-2 mediated MDR through the use of drugs that enable GSH efflux from cells or mitochondria. The significance of this project relates to the problem of MDR in cancer therapeutics. It is our central hypothesis that understanding the biochemical and molecular basis for Bcl-2's ability to block anticancer-drug induced apoptosis will lead to the development of strategies for reversing this drug resistance and enhancing therapeutic effects.