Browne Gillian, Dragon Julie A, Hong Deli, Messier Terri L, Gordon Jonathan A R, Farina Nicholas H, Boyd Joseph R, VanOudenhove Jennifer J, Perez Andrew W, Zaidi Sayyed K, Stein Janet L, Stein Gary S, Lian Jane B
Department of Biochemistry & University of Vermont Cancer Center, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT, 05405, USA.
Department of Microbiology and Molecular Genetics, University of Vermont, 95 Carrigan Avenue, Burlington, VT, 05405, USA.
Tumour Biol. 2016 Jul;37(7):8825-39. doi: 10.1007/s13277-015-4710-6. Epub 2016 Jan 9.
The Runx1 transcription factor, known for its essential role in normal hematopoiesis, was reported in limited studies to be mutated or associated with human breast tumor tissues. Runx1 increases concomitantly with disease progression in the MMTV-PyMT transgenic mouse model of breast cancer. Compelling questions relate to mechanisms that regulate Runx1 expression in breast cancer. Here, we tested the hypothesis that dysregulation of Runx1-targeting microRNAs (miRNAs) allows for pathologic increase of Runx1 during breast cancer progression. Microarray profiling of the MMTV-PyMT model revealed significant downregulation of numerous miRNAs predicted to target Runx1. One of these, miR-378, was inversely correlated with Runx1 expression during breast cancer progression in mice and in human breast cancer cell lines MCF7 and triple-negative MDA-MB-231 that represent early- and late-stage diseases, respectively. MiR-378 is nearly absent in MDA-MB-231 cells. Luciferase reporter assays revealed that miR-378 binds the Runx1 3' untranslated region (3'UTR) and inhibits Runx1 expression. Functionally, we demonstrated that ectopic expression of miR-378 in MDA-MB-231 cells inhibited Runx1 and suppressed migration and invasion, while inhibition of miR-378 in MCF7 cells increased Runx1 levels and cell migration. Depletion of Runx1 in late-stage breast cancer cells resulted in increased expression of both the miR-378 host gene PPARGC1B and pre-miR-378, suggesting a feedback loop. Taken together, our study identifies a novel and clinically relevant mechanism for regulation of Runx1 in breast cancer that is mediated by a PPARGC1B-miR-378-Runx1 regulatory pathway. Our results highlight the translational potential of miRNA replacement therapy for inhibiting Runx1 in breast cancer.
Runx1转录因子在正常造血过程中发挥着重要作用，有限的研究报道其在人类乳腺肿瘤组织中发生突变或与之相关。在MMTV-PyMT乳腺癌转基因小鼠模型中，Runx1随着疾病进展而同步增加。与乳腺癌中调控Runx1表达的机制相关的问题备受关注。在此，我们验证了一个假说，即靶向Runx1的微小RNA（miRNA）失调会导致乳腺癌进展过程中Runx1病理性增加。对MMTV-PyMT模型进行微阵列分析，结果显示众多预测靶向Runx1的miRNA显著下调。其中之一，即miR-378，在小鼠乳腺癌进展过程以及分别代表早期和晚期疾病的人乳腺癌细胞系MCF7和三阴性MDA-MB-231中，与Runx1表达呈负相关。MDA-MB-231细胞中几乎不存在miR-378。荧光素酶报告基因检测显示，miR-378与Runx1的3'非翻译区（3'UTR）结合并抑制Runx1表达。在功能方面，我们证明在MDA-MB-231细胞中异位表达miR-378可抑制Runx1，并抑制细胞迁移和侵袭，而在MCF7细胞中抑制miR-378则会增加Runx1水平和细胞迁移。晚期乳腺癌细胞中Runx1的缺失导致miR-378宿主基因PPARGC1B和前体miR-378的表达均增加，提示存在一个反馈环。综上所述，我们的研究确定了一种由PPARGC1B-miR-378-Runx1调控通路介导的、在乳腺癌中调控Runx1的新的临床相关机制。我们的结果凸显了miRNA替代疗法在抑制乳腺癌中Runx1表达方面的转化潜力。
