A Membrane-Type-1 Matrix Metalloproteinase (MT1-MMP) – Discoidin Domain Receptor 1 Axis Regulates Collagen-Induced Apoptosis in Breast Cancer Cells

During tumour dissemination, invading breast carcinoma cells become confronted with a reactive stroma, a type I collagen-rich environment endowed with anti-proliferative and pro-apoptotic properties. To develop metastatic capabilities, tumour cells must acquire the capacity to cope with this novel microenvironment. How cells interact with and respond to their microenvironment during cancer dissemination remains poorly understood. To address the impact of type I collagen on the fate of tumour cells, human breast carcinoma MCF-7 cells were cultured within three-dimensional type I collagen gels (3D COL1). Using this experimental model, we have previously demonstrated that membrane type-1 matrix metalloproteinase (MT1-MMP), a proteinase overexpressed in many aggressive tumours, promotes tumour progression by circumventing the collagen-induced up-regulation of BIK, a pro-apoptotic tumour suppressor, and hence apoptosis. Here we performed a transcriptomic analysis to decipher the molecular mechanisms regulating 3D COL1-induced apoptosis in human breast cancer cells. Control and MT1-MMP expressing MCF-7 cells were cultured on two-dimensional plastic plates or within 3D COL1 and a global transcriptional time-course analysis was performed. Shifting the cells from plastic plates to 3D COL1 activated a complex reprogramming of genes implicated in various biological processes. Bioinformatic analysis revealed a 3D COL1-mediated alteration of key cellular functions including apoptosis, cell proliferation, RNA processing and cytoskeleton remodelling. By using a panel of pharmacological inhibitors, we identified discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase specifically activated by collagen, as the initiator of 3D COL1-induced apoptosis. Our data support the concept that MT1-MMP contributes to the inactivation of the DDR1-BIK signalling axis through the cleavage of collagen fibres and/or the alteration of DDR1 receptor signalling unit, without triggering a drastic remodelling of the transcriptome of MCF-7 cells.肿瘤播散过程中，侵袭性乳腺癌细胞会遭遇反应性基质——一种富含I型胶原蛋白的微环境，兼具抗增殖与促凋亡特性。肿瘤细胞若要获得转移能力，必须具备适应这种新型微环境的能力。目前，学界对肿瘤播散过程中细胞如何与微环境相互作用并作出应答仍知之甚少。为探究I型胶原蛋白对肿瘤细胞命运的影响，本研究将人乳腺癌MCF-7细胞培养于三维I型胶原蛋白凝胶（three-dimensional type I collagen gels，3D COL1）中。利用该实验模型，我们此前已证实：膜型1基质金属蛋白酶（membrane type-1 matrix metalloproteinase，MT1-MMP）作为一种在多种侵袭性肿瘤中高表达的蛋白酶，可通过阻断胶原蛋白诱导的促凋亡肿瘤抑制因子BIK的上调，进而抑制细胞凋亡，最终促进肿瘤进展。本研究通过转录组分析，解析人乳腺癌细胞中3D COL1诱导凋亡的分子调控机制。我们将对照组及过表达MT1-MMP的MCF-7细胞分别培养于二维塑料培养板与3D COL1中，并开展了全转录组时间序列分析。将细胞从塑料培养板转移至3D COL1环境中，可激活涉及多种生物学过程的复杂基因重编程程序。生物信息学分析显示，3D COL1可介导多种关键细胞功能的改变，包括凋亡、细胞增殖、RNA加工及细胞骨架重塑。我们通过一组药理学抑制剂实验，证实盘状结构域受体1（discoidin domain receptor 1，DDR1）——一种可被胶原蛋白特异性激活的受体酪氨酸激酶——是3D COL1诱导凋亡的起始调控因子。本研究数据支持以下观点：MT1-MMP可通过切割胶原蛋白纤维或/和改变DDR1受体信号复合物，介导DDR1-BIK信号轴的失活，且不会引发MCF-7细胞转录组的显著重编程。