Characterisation of the anti-apoptotic function of P-glycoprotein and transcriptional regulation of the MDR1 gene.

肿瘤细胞在化疗中存活的能力是治疗癌症患者的主要障碍。癌细胞产生多药耐药（MDR）的一个机制是它们获得了一种叫做p -糖蛋白（P-gp）的蛋白质的表达，这种蛋白质将细胞毒性药物挤出癌细胞。我们已经定义了P-gp在保护细胞免受非药物刺激引起的死亡方面的新作用，其中P-gp的外排效应将没有明显的益处。P-gp这种更广泛的生存效应可能是由于它能够调节细胞内存在的关键酶（半胱天冬酶）的活性，从而在适当的时候诱导细胞自杀。许多化疗药物激活半胱天冬酶来杀死靶细胞，由于P-gp可以抑制半胱天冬酶的激活，因此P-gp可能通过将药物从靶细胞中移除和抑制药物杀死细胞的途径来影响抗癌药物的活性。我们对P-gp进行了突变，以确定其caspase调节功能所必需的区域。我们现在正在鉴定与这个区域结合的蛋白质，这样我们就可以确定P-gp如何调节半胱天冬酶的激活。此外，我们已经定义了P-gp在正常细胞中保持低表达的方式，并在细胞暴露于化疗药物后上调表达。编码P-gp （MDR1）的基因通常是关闭的，因为它被包装在一种叫做染色质的核结构中。我们已经证明，用化疗药物治疗癌细胞系会改变染色质，从而激活MDR1基因。我们将确定参与药物介导的染色质结构调节的蛋白质和复合物，并确定这种现象是否发生在接受化疗的患者中。我们的新发现可能会为耐多药癌症患者提供新的治疗选择，并可能提供抑制表达p- gp的耐多药肿瘤形成的可能的新方法。

The ability of tumor cells to survive treatment by chemotherapy is a major obstacle in curing patients with cancer. One mechanism by which cancer cells become multidrug resistant (MDR) is their acquired expression of a protein called P-glycoprotein (P-gp) that extrudes cytotoxic drugs out of the cancer cell. We have defined a novel role for P-gp in protecting cells against death induced by non-drug stimuli, where an efflux effect of P-gp would have no obvious benefit. This broader survival effect of P-gp may be explained by its ability to regulate the activity of key enzymes (caspases) that exist within cells to induce cell suicide when appropriate. Many chemotherapeutic drugs activate caspases to kill target cells and as P-gp can inhibit caspase activation, it is therefore possible that P-gp affects the activity of anti-cancer drugs by both removing the drugs from the target cells and inhibiting the pathways through which the drugs can kill a cell. We have mutated P-gp to define the region that is necessary for its caspase regulatory function. We are now identifying the proteins that bind to this region so that we can determine how P-gp regulates caspase activation. In addition, we have defined the manner by which P-gp expression is kept low in normal cells and is upregulated following exposure of cells to chemotherapeutic drugs. The gene encoding P-gp (MDR1) is normally switched off due to the way it is packaged within a nuclear structure called chromatin. We have shown that treatment of cancer cell lines with chemotherapeutic drugs alters chromatin in such a way that the MDR1 gene is activated. We will identify the proteins and complexes involved in drug-mediated regulation of chromatin structure and determine if this phenomenon occurs within patients receiving chemotherapy. Our new findings may lead to novel treatment options for patients that have MDR cancers and may provide insight into possible new ways to inhibit the formation of P-gp-expressing MDR tumors.