The histone variant macroH2A modulates inflammatory response in cancer [UMI-4C]

MacroH2A histone variants have a major role in nuclear organization and large-scale 3D chromatin architecture. How these alterations impinge on the behaviour of cancer cells is not known. Here, we describe the analysis of the total macroH2A loss of function phenotype in a model of hepatoblastoma, the main childhood liver cancer. Performing transcriptomic analyses in xenografts and cell cultures, we find that macroH2A modulated the response of cancer cells to paracrine inflammatory signalling. Specifically, ablation of macroH2A ablation neutralized the induction of a large subset of genes by TNFα and led to the hyperactivation of another subset of genes. Among the top macroH2A-sensitive genes we find the cancer-related gene DKK1 . Depletion of macroH2A rendered the DKK1 gene hypersensitive to TNFα signalling boosting the secretion of DKK1 protein. On the gene regulation level, this was mediated by an alteration of the local chromatin structure and facilitated activation of distal enhancer elements. The study of human samples of hepatoblastoma showed that DKK1 is strongly upregulated in tumors and associated with poor patient outcome. Taken together our results suggest that the regulation of 3D chromatin architecture by macroH2A histone variants has a central role in the response and regulation of paracrine signalling that might be relevant for the interaction of cancers with immune cells and other cells in their microenvironment. UMI-4C assays performed in HepG2 cell lines stably expressing either control shRNAs (CTL) or shRNAs targeting macroH2A1 and macroH2A2 (DKD)

MacroH2A组蛋白变体（MacroH2A histone variants）在细胞核组织与大规模三维染色质架构中发挥核心调控作用。目前学界尚未明确这类组蛋白变体的改变如何影响癌细胞的生物学行为。本研究以儿童原发性肝癌——肝母细胞瘤的模型为对象，开展了完全性MacroH2A功能丧失表型的分析。通过对异种移植瘤与细胞培养样本进行转录组学分析，我们发现MacroH2A可调控癌细胞对旁分泌炎症信号的响应。具体而言，敲除MacroH2A可中和肿瘤坏死因子α（TNFα）对大量基因子集的诱导效应，并触发另一部分基因子集的过度激活。在MacroH2A敏感的核心基因中，我们鉴定出癌相关基因DKK1。敲除MacroH2A会使DKK1基因对TNFα信号的响应性显著增强，进而促进DKK1蛋白的分泌。在基因调控层面，该过程通过改变局部染色质结构介导，并促进了远端增强子元件的激活。对肝母细胞瘤患者临床样本的分析显示，DKK1在肿瘤组织中显著上调，且与患者不良预后密切相关。综合以上结果，我们认为MacroH2A组蛋白变体对三维染色质架构的调控，在旁分泌信号的响应与调控中扮演核心角色，这一机制可能与癌细胞及其微环境中免疫细胞和其他细胞的相互作用密切相关。本研究在稳定表达对照短发夹RNA（CTL）或靶向MacroH2A1与MacroH2A2的短发夹RNA（DKD）的HepG2细胞系中开展了UMI-4C实验。