Dong Yiyu, Van Tine Brian A, Oyama Toshinao, Wang Patricia I, Cheng Emily H, Hsieh James J
Human Oncology & Pathogenesis Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
Department of Internal Medicine, Washington University, St Louis, MO 63110, USA.
Cell Res. 2014 Nov;24(11):1354-66. doi: 10.1038/cr.2014.129. Epub 2014 Sep 30.
Taspase1, a highly conserved threonine protease, cleaves nuclear transcriptional regulators mixed-lineage leukemia (MLL, MLL1), MLL2, TFIIA, and ALF to orchestrate a wide variety of biological processes. In vitro studies thus far demonstrated that Taspase1 plays important roles in the proliferation of various cancer cell lines, including HER2-positive breast cancer cells. To investigate the role of Taspase1 in breast tumorigenesis in vivo, we deleted Taspase1 from mouse mammary glands by generating MMTV-neu;MMTV-cre;Tasp1(F/-) mice. We demonstrate that initiation of MMTV-neu- but not MMTV-wnt-driven breast cancer is blocked in the absence of Taspase1. Importantly, Taspase1 loss alone neither impacts normal development nor pregnancy physiology of the mammary gland. In mammary glands Taspase1 deficiency abrogates MMTV-neu-induced cyclins E and A expression, thereby preventing tumorigenesis. The mechanisms were explored in HER2-positive breast cancer cell line BT474 and HER2-transformed MCF10A cells and validated using knockdown-resistant Taspase1. As Taspase1 was shown to cleave MLL which forms complexes with E2F transcription factors to regulate Cyclins E, A, and B expression in mouse embryonic fibroblasts (MEFs), we investigated whether the cleavage of MLL by Taspase1 constitutes an essential in vivo axis for HER2/neu-induced mammary tumorigenesis. To this end, we generated MMTV-neu;MLL(nc/nc) transgenic mice that carry homozygous non-cleavable MLL alleles. Remarkably, these mice are also protected from HER2/neu-driven breast tumorigenesis. Hence, MLL is the primary Taspase1 substrate whose cleavage is required for MMTV-neu-induced tumor formation. As Taspase1 plays critical roles in breast cancer pathology, it may serve as a therapeutic target for HER2-positive human breast cancer.
Taspase1是一种高度保守的苏氨酸蛋白酶，可切割核转录调节因子混合谱系白血病（MLL，MLL1）、MLL2、TFIIA和ALF，以协调多种生物学过程。迄今为止的体外研究表明，Taspase1在包括HER2阳性乳腺癌细胞在内的各种癌细胞系的增殖中发挥重要作用。为了研究Taspase1在体内乳腺肿瘤发生中的作用，我们通过构建MMTV-neu;MMTV-cre;Tasp1(F/-)小鼠，从小鼠乳腺中删除了Taspase1。我们证明，在没有Taspase1的情况下，MMTV-neu驱动而非MMTV-wnt驱动的乳腺癌起始受到阻断。重要的是，单独缺失Taspase1既不影响乳腺的正常发育，也不影响妊娠生理。在乳腺中，Taspase1缺乏会消除MMTV-neu诱导的细胞周期蛋白E和A的表达，从而预防肿瘤发生。我们在HER2阳性乳腺癌细胞系BT474和HER2转化的MCF10A细胞中探索了其机制，并使用抗敲低的Taspase1进行了验证。由于Taspase1已被证明可切割MLL，MLL与E2F转录因子形成复合物以调节小鼠胚胎成纤维细胞（MEF）中的细胞周期蛋白E、A和B的表达，我们研究了Taspase1对MLL的切割是否构成HER2/neu诱导的乳腺肿瘤发生的体内关键轴。为此，我们构建了携带纯合不可切割MLL等位基因的MMTV-neu;MLL(nc/nc)转基因小鼠。值得注意的是，这些小鼠也受到保护，免受HER2/neu驱动的乳腺肿瘤发生。因此，MLL是Taspase1的主要底物，其切割是MMTV-neu诱导的肿瘤形成所必需的。由于Taspase1在乳腺癌病理中起关键作用，它可能成为HER2阳性人类乳腺癌的治疗靶点。
