Pygo2在乳腺癌多药耐药中的作用及其上下游分子机制

Multidrug resistance plays a prominent role in treatment failure and recurrence of breast cancer. It has been demonstrated that the expression of MDR1 is the major cause for multidrug resistance of cancer; however, the factors which activate the MDR1 expression remain largely unknown. Our previous experiments of this proposal showed that Pygo2 is overexpressed in chemoresistant MCF7/MDR breast cancer cells and directly upregulats MDR1 expression.Further study indicated that Pygo2 may bind to a novel TCF site on MDR1 promoter, which suggests that Pygo2 probablly participates in chemoresistance signal transduction via Wnt signaling in upstream. Moreover, Pygo2 was found to associate with PCAF, a histone acetyltransferase in MCF7/MDR cells, which suggests that Pygo2 probablly activates MDR1 expression by epigenetic mechanism in downstream. Our previous experiments also showed that loss of function of Pygo2 could recover the sensitivity of MCF7/MDR cells to chemotherapy， suggestive of its role in mediating multidrug resistance of cancer. Furthrmore, Pygo2 was found to expand the size of breast cancer stem cells and this ability is dependent on the MDR1. In this proposal, we will systematically study the mechanism and function of Pygo2 in mediating the formation of multidrug resistance of breast cancer, in molecular, cellular, gene modified mouse tumor model and clinical tumor sample levels. Our study will reveal a possibality that Pygo2 may act as a nonel target for diagnosis and treatment of chemoresistance of breast cancer.

多药耐药是乳腺癌治疗失败与复发的主要原因，以往研究证明MDR1表达是引起多药耐药的主要原因，但引起其表达增高的因素仍所知甚少。我们前期研究发现，Pygo2在乳腺癌耐药细胞系中表达明显增高，并且能直接调控MDR1的表达；进一步研究证明，Pygo2结合于MDR1启动子一个新的TCF位点，表明Pygo2在上游可能通过Wnt信号参与了耐药信号转导。我们还发现Pygo2在耐药细胞株中可以与乙酰基转移酶PCAF结合，表明Pygo2在下游可能通过表观调控染色质促进耐药基因表达。我们前期研究还显示，Pygo2的失活能恢复耐药细胞株的敏感性，提示Pygo2在肿瘤多药耐药的形成中发挥重要作用。此外，Pygo2还能增加乳腺癌细胞的干细胞群，并且依赖于MDR1。本课题将在分子、细胞、基因修饰小鼠以及临床标本水平系统研究Pygo2在乳腺癌多药耐药形成中的作用以及机制，探讨Pygo2作为乳腺癌耐药诊断治疗靶点的可能。

多药耐药是乳腺癌治疗失败与复发的主要原因，以往研究证明MDR1表达是引起多药耐药的主要原因，但引起其表达增高的因素仍所知甚少，本研究鉴定出调节这一过程的关键分子。我们的研究发现，Wnt/β-catenin信号通路在化疗耐药细胞株中被激活，利用Wnt信号通路特异性PCR array筛选出Pygo2为在耐药细胞中上调表达最明显的基因，并且能直接调控MDR1的表达；进一步研究证明，Pygo2结合于MDR1启动子一个新的TCF位点，证明Pygo2在上游通过Wnt信号参与了耐药信号转导。我们研究还显示，Pygo2的失活能恢复耐药细胞株的敏感性，表明Pygo2在肿瘤多药耐药的形成中发挥重要作用。此外，Pygo2还能增加乳腺癌细胞的干细胞群，并且依赖于MDR1。最后，为了研究Pygo2与临床化疗的乳腺癌患者的关联，我们对配对经穿刺活检确诊或手术局部晚期乳腺癌后获得的新辅助化疗6个疗程的64例患者的队列肿瘤样本（LABC; IIB期和III）进行了分析。发现化疗后产生耐药的病例中Pygo2与MDR1表达同步上升，关联性显著。本课题在分子、细胞、基因修饰小鼠以及临床标本水平系统研究了Pygo2在乳腺癌多药耐药形成中的作用以及机制，提示Pygo2作为乳腺癌耐药诊断治疗靶点的可能性。

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