Thewes V, Simon R, Hlevnjak M, Schlotter M, Schroeter P, Schmidt K, Wu Y, Anzeneder T, Wang W, Windisch P, Kirchgäßner M, Melling N, Kneisel N, Büttner R, Deuschle U, Sinn H P, Schneeweiss A, Heck S, Kaulfuss S, Hess-Stumpp H, Okun J G, Sauter G, Lykkesfeldt A E, Zapatka M, Radlwimmer B, Lichter P, Tönjes M
Division of Molecular Genetics, German Cancer Consortium (DKTK), German Cancer Research Center (DKFZ), Heidelberg, Germany.
Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Oncogene. 2017 Jul 20;36(29):4124-4134. doi: 10.1038/onc.2017.32. Epub 2017 Mar 20.
Antiestrogen-resistant and triple-negative breast tumors pose a serious clinical challenge because of limited treatment options. We assessed global gene expression changes in antiestrogen-sensitive compared with antiestrogen-resistant (two tamoxifen resistant and two fulvestrant resistant) MCF-7 breast cancer cell lines. The branched-chain amino acid transaminase 1 (BCAT1), which catalyzes the first step in the breakdown of branched-chain amino acids, was among the most upregulated transcripts in antiestrogen-resistant cells. Elevated BCAT1 expression was confirmed in relapsed tamoxifen-resistant breast tumor specimens. High intratumoral BCAT1 levels were associated with a reduced relapse-free survival in adjuvant tamoxifen-treated patients and overall survival in unselected patients. On a tissue microarray (n=1421), BCAT1 expression was detectable in 58% of unselected primary breast carcinomas and linked to a higher Ki-67 proliferation index, as well as histological grade. Interestingly, BCAT1 was predominantly expressed in estrogen receptor-α-negative/human epidermal growth factor receptor-2-positive (ERα-negative/HER-2-positive) and triple-negative breast cancers in independent patient cohorts. The inverse relationship between BCAT1 and ERα was corroborated in various breast cancer cell lines and pharmacological long-term depletion of ERα induced BCAT1 expression in vitro. Mechanistically, BCAT1 indirectly controlled expression of the cell cycle inhibitor p27 thereby affecting pRB. Correspondingly, phenotypic analyses using a lentiviral-mediated BCAT1 short hairpin RNA knockdown revealed that BCAT1 sustains proliferation in addition to migration and invasion and that its overexpression enhanced the capacity of antiestrogen-sensitive cells to grow in the presence of antiestrogens. Importantly, silencing of BCAT1 in an orthotopic triple-negative xenograft model resulted in a massive reduction of tumor volume in vivo, supporting our findings that BCAT1 is necessary for the growth of hormone-independent breast tumors.
抗雌激素耐药和三阴性乳腺癌由于治疗选择有限，构成了严峻的临床挑战。我们评估了抗雌激素敏感的与抗雌激素耐药的（两种他莫昔芬耐药和两种氟维司群耐药）MCF-7乳腺癌细胞系中的全球基因表达变化。催化支链氨基酸分解第一步的支链氨基酸转氨酶1（BCAT1）是抗雌激素耐药细胞中上调最明显的转录本之一。在复发的他莫昔芬耐药乳腺肿瘤标本中证实了BCAT1表达升高。肿瘤内BCAT1水平高与接受辅助他莫昔芬治疗患者的无复发生存期缩短以及未选择患者的总生存期缩短相关。在组织微阵列（n = 1421）上，58%的未选择原发性乳腺癌中可检测到BCAT1表达，且其与较高的Ki-67增殖指数以及组织学分级相关。有趣的是，在独立患者队列中，BCAT1主要表达于雌激素受体-α阴性/人表皮生长因子受体-2阳性（ERα阴性/HER-2阳性）和三阴性乳腺癌中。BCAT1与ERα之间的负相关在多种乳腺癌细胞系中得到证实，并且ERα的药理学长期耗竭在体外诱导了BCAT1表达。从机制上讲，BCAT1间接控制细胞周期抑制剂p27的表达，从而影响pRB。相应地，使用慢病毒介导的BCAT1短发夹RNA敲低进行的表型分析表明，BCAT1除了维持迁移和侵袭外还维持增殖，并且其过表达增强了抗雌激素敏感细胞在抗雌激素存在下生长的能力。重要的是，在原位三阴性异种移植模型中沉默BCAT1导致体内肿瘤体积大幅减小，支持了我们的发现，即BCAT1是激素非依赖性乳腺肿瘤生长所必需的。
