Department of Surgical Oncology, MD Anderson Cancer Center, Houston, TX 77030, USA.
Oncogene. 2010 Jul 8;29(27):3896-907. doi: 10.1038/onc.2010.151. Epub 2010 May 10.
HER2/neu (HER2) and cyclin E are important prognostic indicators in breast cancer. As both are involved in cell cycle regulation we analyzed whether there was a direct interaction between the two. HER2 and cyclin E expression levels were determined in 395 breast cancer patients. Patients with HER2-overexpression and high levels of cyclin E had decreased 5-year disease-specific survival compared with low levels of cyclin E (14% versus 89%, P<0.0001). In vitro studies were performed in which HER2-mediated activity in HER2-overexpressing breast cancer cell lines was downregulated by transfection with HER2 small interfering RNA or treatment with trastuzumab. Cyclin E expression levels were determined by western blot analysis, and functional effects analyzed using kinase assays, MTT assays were used to assess cell viability as a marker of proliferation and fluorescence-activated cell sorting analysis was used to determine cell cycle profiles. Decreased HER2-mediated signaling resulted in decreased expression of cyclin E, particularly the low molecular weight (LMW) isoforms. Decreased HER2 and LMW cyclin E expression had functional consequences, including decreased cyclin E-associated kinase activity and decreased proliferation, because of increased apoptosis and an increased accumulation of cells in the G1 phase. In vivo studies performed in a HER2-overexpressing breast cancer xenograft model confirmed the effects of trastuzumab on cyclin E expression. Given the relationship between HER2 and cyclin E, in vitro clonogenic assays were performed to assess combination therapy targeting both proteins. Isobologram analysis showed a synergistic interaction between the two agents (trastuzumab targeting HER2 and roscovitine targeting cyclin E). Taken together, these studies show that HER2-mediated signaling effects LMW cyclin E expression, which in turn deregulates the cell cycle. LMW cyclin E has prognostic and predictive roles in HER2-overexpressing breast cancer, warranting further study of its potential as a therapeutic target.
HER2/neu（HER2）和细胞周期蛋白 E 是乳腺癌的重要预后指标。由于两者都参与细胞周期调控，我们分析了它们之间是否存在直接相互作用。在 395 例乳腺癌患者中测定了 HER2 和细胞周期蛋白 E 的表达水平。与细胞周期蛋白 E 低水平的患者相比，HER2 过表达和高水平细胞周期蛋白 E 的患者 5 年疾病特异性生存率降低（14%比 89%，P<0.0001）。在体外研究中，通过用 HER2 小干扰 RNA 转染或用曲妥珠单抗处理，下调 HER2 过表达乳腺癌细胞系中的 HER2 介导的活性，测定细胞周期蛋白 E 的表达水平，并通过激酶测定分析功能效应，用 MTT 测定法评估细胞活力作为增殖的标志物，用荧光激活细胞分选分析确定细胞周期谱。HER2 介导的信号转导减少导致细胞周期蛋白 E 的表达减少，特别是低分子量（LMW）同工型。HER2 和 LMW 细胞周期蛋白 E 表达的减少具有功能后果，包括细胞周期蛋白 E 相关激酶活性降低和增殖减少，因为凋亡增加和 G1 期细胞积累增加。在 HER2 过表达的乳腺癌异种移植模型中进行的体内研究证实了曲妥珠单抗对细胞周期蛋白 E 表达的影响。鉴于 HER2 和细胞周期蛋白 E 之间的关系，进行了体外集落形成测定以评估针对这两种蛋白质的联合治疗。等效应线分析表明两种药物（针对 HER2 的曲妥珠单抗和针对细胞周期蛋白 E 的罗昔司汀）之间存在协同相互作用。总之，这些研究表明，HER2 介导的信号转导影响 LMW 细胞周期蛋白 E 的表达，从而使细胞周期失调。LMW 细胞周期蛋白 E 在 HER2 过表达的乳腺癌中具有预后和预测作用，值得进一步研究其作为治疗靶点的潜力。
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