Regulation of p130Cas/BCAR1 Expression in Tamoxifen-Sensitive and Tamoxifen-Resistant Breast Cancer Cells by EGR1 and NAB2
Regulation of p130Cas/BCAR1 Expression in Tamoxifen-Sensitive and Tamoxifen-Resistant Breast Cancer Cells by EGR1 and NAB2
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DOI：
10.1593/neo.111760
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发表时间：
2012-02-01
期刊：
影响因子：
4.8
通讯作者：
Kirsch, Kathrin H.
中科院分区：
文献类型：
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作者：
Kumbrink, Joerg;Kirsch, Kathrin H.
在侵袭性乳腺肿瘤中发现p130(Cas)/BCAR1(Crk相关底物/乳腺癌抗雌激素耐药1)水平升高，并与乳腺癌的他莫昔芬耐药有关。P130(Cas)促进多种信号转导通路中蛋白复合体的整合，这些信号转导通路在乳腺癌中经常失控。为了阐明乳腺癌中p130(Cas)表达上调以及获得性三苯氧胺耐药的机制，我们研究了p130(Cas)/BCAR1的调节。由于在BCAR1的5‘端发现了可诱导转录因子Egr1的多个可能的结合基序，因此我们研究了Egr1及其辅助调节因子NAB2对p130(Cas)/BCAR1的调控。过表达或短干扰RNA(SiRNA)介导的Egr1或NAB2的下调以及染色质免疫沉淀表明Egr1和NAB2协同作用正向调节乳腺癌细胞中p130(Cas)/BCAR1的表达。对p130(Cas)的siRNA去除表明，在对他莫昔芬敏感的MCF-7细胞中，p130(Cas)调节Egr1和NAB_2的表达，而在对他莫昔芬耐药的-R细胞中，仅NAB_2水平受到影响。佛波酯上调BCAR1RNA和p130(Cas)蛋白的表达遵循MCF-7细胞晚期反应基因的动力学规律，而对-R细胞则无此作用。因此，在MCF-7细胞中，我们发现了一个正反馈环，其中p130(Cas)正向调节Egr1和NAB2，进而诱导p130(Cas)的表达。重要的是，与MCF-7相比，-R中NAB2的表达增强和Egr1与BCAR15‘端结合增加可能导致-R细胞中p130(Cas)/BCAR1的结构性升高。MCF-7和-R细胞中EGR1/NAB2/p130(Cas)网络中未发现的差异也可能是获得性他莫昔芬耐药过程中p130(Cas)上调的原因之一。
Elevated levels of p130(Cas)/BCAR1 (Crk-associated substrate/breast cancer antiestrogen resistance 1) are found in aggressive breast tumors and are associated with tamoxifen resistance of mammary cancers. p130(Cas) promotes the integration of protein complexes involved in multiple signaling pathways frequently deregulated in breast cancer. To elucidate mechanisms leading to p130(Cas) up-regulation in mammary carcinomas and during acquired tamoxifen resistance, the regulation of p130(Cas)/BCAR1 was studied. Because multiple putative binding motifs for the inducible transcription factor EGR1 were identified in the 5' region of BCAR1, the p130(Cas)/BCAR1 regulation by EGR1 and its coregulator NAB2 was investigated. Overexpression or short interfering RNA (siRNA)-mediated down-regulation of EGR1 or NAB2, and chromatin immunoprecipitations indicated that EGR1 and NAB2 act in concert to positively regulate p130(Cas)/BCAR1 expression in breast cancer cells. p130(Cas) depletion using siRNA showed that, in tamoxifen-sensitive MCF-7 cells, p130(Cas) regulates EGR1 and NAB2 expression, whereas in the derivative tamoxifen-resistant TAM-R cells, only NAB2 levels were influenced. BCAR1 messenger RNA and p130(Cas) protein were upregulated by phorbol esters following the kinetics of late response genes in MCF-7 but not in TAM-R cells. Thus, in MCF-7 cells, we identified a positive feedback loop where p130(Cas) positively regulates EGR1 and NAB2, which in turn induce p130(Cas) expression. Importantly, compared with MCF-7, enhanced NAB2 expression and increased EGR1 binding to the BCAR1 5' region observed in TAM-R may lead to the constitutively increased p130(Cas)/BCAR1 levels in TAM-R cells. The uncovered differences in this EGR1/NAB2/p130(Cas) network in MCF-7 versus TAM-R cells may also contribute to p130(Cas) up-regulation during acquired tamoxifen resistance.