蛋白质异构化酶PIMT1在乳腺癌三苯氧胺耐药中的作用机制研究

Tamoxifen (Tam) is the most often prescribed antiestogen for breast cancers, while Tam resistance (TR) remains one of the most critical obstacle for breast cancer management. Our preliminary data showed that the Protein L-isoaspartyl Methyltransferase I (PIMT1) is a binding protein of Hsp27 which is related to breast cancer sensitivity to chemotherapeutic drugs, then we discovered that lower expression of PIMT1 is correlated with TR in both human breast tumors and cell lines, and knockdown of PIMT1 renders breast cancer cells TR. Therefore we hypothesized that lower expression of PIMT1 might be causal for breast cancer TR. In this proposal, we will extend our preliminary studies to define the mechanisms underlying PIMT1 related TR, determine whether Hsp27 is a putative substrate for PIMT1 and involved in PIMT1 related TR. The Specific Aims are:.1.To determine whether lower expression of PIMT1 could confer breast cancer cells TR..We have demonstrated that knockdown of PIMT1 renders MCF-7 cells TR, we will extend to study knockdown PIMT1 in T47D and MDA-MB-361 or overexpressing PIMT1 in MCF-7TR (PIMT1 low) cells could alter their sensitivity to Tam in both cell culture and xenografts, we will also identify TR related PIMT1 substrates using proteomic approaches..2.To examine whether PIMT1 could affect ERα and other TR related factors..We will use different approaches to study the effect of PIMT1 on the expression and activity of ERα, the expression of ERα regulated genes, as well as the expression and activation of other effectors including Her 2, AKT and MAPK..3.To determine whether Hsp27 is involved in PIMT1 related TR and uncover the potential mechanism(s)..We have generated Hsp27-konckdown MCF-7 and –overexpressing MDA-MB-361 cells, as well as MCF-7TR and PIMT1 knckdown MCF-7 cells. We will further modify the expression of Hsp27 and PIMT1 in these cell lines to observe their cross-regulation and the impact on breast cancer cells response to Tam, in both cell culture and xenografts.

三苯氧胺（Tam）是应用最广的抗雌激素药物，其耐药（TR）的发生是乳腺癌临床中最重要的问题之一。我们首先发现与乳腺癌耐药有关的Hsp27可结合蛋白质天冬氨酸甲基转移酶PIMT1，继而发现PIMT1在TR的乳腺肿瘤标本和细胞株中均呈显著的低表达，且可以独立的指示乳腺癌患者TR；在敲减PIMT1后，MCF-7细胞在软琼脂中的生长不再对Tam敏感，提示PIMT1的缺失或降低可导致TR的发生。本研究将阐明PIMT1在乳腺癌TR发生中的作用机制，并将探讨Hsp27是否是一个新的PIMT1底物以及是否涉及到PIMT1低表达所导致的TR和具体的机制。本研究将确定PIMT1和Hsp27的结合能否成为可预测乳腺癌TR的更可靠的生物标志和治疗靶点。

三苯氧胺是临床上应用最为广泛的抗雌激素药物，因其耐药现象很严重，因而发现新的耐药标志物以在临床早期选择合适的治疗是非常必要的。本项目主要研究一个蛋白质甲基化酶PIMT1 在三苯氧胺耐药发生中的作用和指导意义。.1， 我们已经通过免疫组化在100多例乳腺癌标本中检测了PIMT1的表达，发现其低表达与三苯氧胺的不良预后显著相关；.2， 与此同时，我们还发现另外一种蛋白质甲基化酶同时又是 DNA甲基转移酶 N6A MT1 的低表达也会导致三苯氧胺耐药，可能与对PI3KCA 表达的活化有关；.3， 我们还通过对DNA甲基化大数据的分析，发现HOXA9 的低表达与三苯氧胺耐药有关。