UBR7 in concert with EZH2 inhibits the TGF-ß signalling leading to extracellular matrix remodelling [ChIP-seq]

The intricate interplay between resident cells and the extracellular matrix (ECM) wields a profound influence on cancer progression. In Triple Negative Breast Cancer (TNBC), ECM architecture evolves primarily due to the enrichment of lysyl oxidase, fibronectin, and collagen that eventually promote distant metastasis. Here, we have uncovered a pivotal transcription regulatory mechanism of the epigenetic regulator UBR7 in conjunction with histone methyltransferase EZH2 in regulating TGF-b/Smad signalling-axis thereby fine-tuning the ECM genes. Remarkably, UBR7 loss leads to a dramatic reduction in the facultative heterochromatin mark H3K27me3 in chromatin, leading to ECM genes firing. Apart from playing a seminal role in matrix deposition in adherent-cancer cells and spheroids, UBR7 alters the total collagen content and lysyl oxidase activity thereby directly impacting the matrix stiffness and consequently its invasive properties. These results can be further translated to TNBC-patients, where reduced RNA/protein levels of UBR7 is accompanied by heightened expression of the ECM-components and their functional-activity which is responsible for fibrosis-mediated matrix stiffness. Thus, UBR7 acts as a master regulator of TNBC matrix-stiffening thereby impacting its metastatic potential. Overall design: Chromatin immunoprecipitation DNA sequencing (ChIP seq) for histone modifications H3K27me3 in stable cells transfected with scrambled RNA and UBR7-Sh vector.

驻留细胞与细胞外基质（extracellular matrix, ECM）之间的复杂互作，对癌症进展具有深远影响。在三阴性乳腺癌（Triple Negative Breast Cancer, TNBC）中，细胞外基质架构的重塑主要源于赖氨酰氧化酶、纤连蛋白与胶原蛋白的富集，最终促进肿瘤远处转移。本研究揭示了表观遗传调控因子UBR7与组蛋白甲基转移酶EZH2协同发挥的关键转录调控机制：二者通过调控转化生长因子β/Smad（TGF-β/Smad）信号轴，进而精准调控细胞外基质相关基因的表达。值得注意的是，UBR7的缺失会导致染色质上的兼性异染色质标记H3K27me3水平显著降低，从而激活细胞外基质相关基因的转录。除了在贴壁癌细胞与细胞球体的基质沉积过程中发挥核心作用外，UBR7还可通过改变总胶原蛋白含量与赖氨酰氧化酶活性，直接影响基质刚度，进而改变肿瘤的侵袭特性。上述研究结果可进一步推广至三阴性乳腺癌患者群体：UBR7的RNA与蛋白水平降低，往往伴随细胞外基质组分的高表达及其功能活性增强，而这正是纤维化介导的基质刚度升高的诱因。因此，UBR7作为三阴性乳腺癌基质硬化的主调控因子，可直接影响肿瘤的转移潜能。实验总体设计：针对转染了阴性对照RNA与UBR7短发夹RNA载体的稳定细胞系，开展组蛋白修饰H3K27me3的染色质免疫沉淀测序（Chromatin immunoprecipitation DNA sequencing, ChIP seq）。