Matrix stiffness induces a tumorigenic phenotype in mammary epithelium through changes in chromatin accessibility. Matrix stiffness induces a tumorigenic phenotype in mammary epithelium through changes in chromatin accessibility

In breast cancer, the increased stiffness of the extracellular matrix (ECM) is a key driver of malignancy. Yet little is known about the epigenomic changes that underlie the tumorigenic impact of ECM mechanics. Here, we show in a 3D culture model of breast cancer that stiff ECM induces a tumorigenic phenotype through changes in chromatin state. We found that increased stiffness yielded cells with more wrinkled nuclei and with increased lamina-associated chromatin, that cells cultured in stiff matrices displayed more accessible chromatin sites, which exhibited footprints of Sp1 binding, and that Sp1 acts along with histone deacetylases (HDAC) 3 and 8 to regulate the induction of stiffness-mediated tumorigenicity. Just as cell culture on soft environments or in them rather than on tissue-culture plastic better recapitulates the acinar morphology observed in mammary epithelium in vivo, mammary epithelial cells cultured on soft microenvironments or in them also more closely replicate the in vivo chromatin state. Our results emphasize the importance of culture conditions for epigenomic studies, and reveal that chromatin state is a critical mediator of mechanotransduction. Overall design: Examination of chromatin accessibility profiles of mammary epithelial cells in hydrogel culture of different stiffness

在乳腺癌中，细胞外基质（ECM）硬度升高是恶性肿瘤发生的关键驱动因素。然而，对于细胞外基质力学特性介导的致瘤效应背后的表观基因组变化，目前仍知之甚少。本研究基于乳腺癌三维培养模型，发现坚硬的细胞外基质可通过改变染色质状态诱导肿瘤发生表型。我们观察到：基质硬度升高会使细胞的细胞核褶皱更多，核纤层结合染色质水平上升；在坚硬基质中培养的细胞拥有更多开放染色质位点，且这些位点存在Sp1结合的特征足迹；同时Sp1与组蛋白去乙酰化酶（HDAC）3和8协同作用，调控硬度介导的致瘤性的诱导。正如在软质环境而非传统组织培养塑料表面进行细胞培养，能够更好地重现体内乳腺上皮的腺泡形态，在软质微环境中培养的乳腺上皮细胞，其染色质状态也更贴近体内真实情况。本研究结果凸显了培养条件在表观基因组研究中的重要性，并揭示染色质状态是机械转导的关键介导因子。总体实验设计：检测不同硬度水凝胶培养体系中乳腺上皮细胞的染色质开放谱。