Dominant CIZ1 fragments drive epigenetic instability and are expressed in early stage cancers
Dominant CIZ1 fragments drive epigenetic instability and are expressed in early stage cancers
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DOI：
10.1101/2023.09.22.558821
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发表时间：
2023-09
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通讯作者：
Gabrielle L. Turvey;Ernesto López de Alba;Emma R Stewart;Lewis Byrom;Heather Cook;Sajad Sofi;Ahmad Alalti;J. Ainscough;Andrew Mason;A. Antson;D. Coverley
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作者：
Gabrielle L. Turvey;Ernesto López de Alba;Emma R Stewart;Lewis Byrom;Heather Cook;Sajad Sofi;Ahmad Alalti;J. Ainscough;Andrew Mason;A. Antson;D. Coverley
CIZ 1是一种核基质蛋白，是在雌性细胞中的失活X染色体（Xi）处形成的大型RNA依赖性超分子组装复合物（SMAC）的一部分，并且在雄性和雌性细胞中的整个细胞核中形成较小的组装体。它通过稳定多梳抑制复合物（PRC）1和2添加的组蛋白翻译后修饰H2 AK 119 ub 1和H3 K27 me 3，在维持分化细胞的表观遗传状态和基因表达方面发挥作用。在这里，我们表明，N-末端复制域（RD）和C-末端锚结构域（AD）的人类CIZ 1转录的表达是不耦合的，与持续升高的AD在早期乳腺癌，和零星升高的AD在其他常见的实体瘤。在蛋白质水平上，CIZ 1-Xi SMAC在女性乳腺癌细胞中被破坏，并且这伴随着AD编码转录物的升高。我们模拟了AD片段在原代小鼠胚胎成纤维细胞中的作用，并观察到在G1期早期的组装过程中对CIZ 1 SMACs的显性负干扰。诱变鉴定matrin 3同源结构域对于自身相互作用以在体外形成稳定的同源二聚体是必需的，并且是其在细胞中的显性负效应的决定因素，这暗示了CIZ 1 SMAC完整性中的二聚化界面。SMAC破坏与PR依赖性H2 AK 119 ub 1从Xi染色质中的消耗一致，PR-去泛素化酶抑制剂PR 619以一种废除的方式消除，表明CIZ 1 SMAC通常通过屏蔽Xi染色质免受去泛素化酶攻击来稳定H2 AK 119 ub 1。此外，SMAC破坏伴随着几天内基因表达的变化。总之，这些数据表明，CIZ 1 AD片段的不适当表达可能通过使通常保护抑制的染色质的CIZ 1 SMAC不稳定来驱动早期乳腺癌中的表观遗传不稳定性。
CIZ1 is a nuclear matrix protein that is part of the large RNA-dependent supramolecular assembly complexes (SMACs) that form at the inactive X chromosome (Xi) in female cells, and smaller assemblies throughout the nucleus in males and females. It plays a role in maintenance of epigenetic state and gene expression in differentiated cells, via stabilisation of histone post-translational modifications H2AK119ub1 and H3K27me3, added by polycomb repressive complexes (PRC) 1 and 2. Here, we show that expression of the N-terminal replication domain (RD) and C-terminal anchor domain (AD) of human CIZ1 transcript is uncoupled, with consistently elevated AD in early stage breast cancers, and sporadically elevated AD in other common solid tumours. At the protein level CIZ1-Xi SMACs are corrupted in female breast cancers cells, and this is accompanied by elevated AD-encoding transcripts. We modelled the effect of AD fragments in primary murine embryonic fibroblasts and observed dominant-negative interference with CIZ1 SMACs during their assembly in early G1 phase. Mutagenesis identified the matrin 3 homology domain as essential for self-interaction to form stable homodimers in vitro, and as a determinant of its dominant-negative effect in cells, implicating the dimerization interface in CIZ1 SMAC integrity. SMAC disruption was coincident with depletion of PRC1-dependent H2AK119ub1 from Xi chromatin, in a manner abrogated by the PR-deubiquitinase inhibitor PR619, suggesting that CIZ1 SMACs normally stabilise H2AK119ub1 by shielding Xi chromatin from attack by deubiquitinases. Moreover, SMAC disruption was accompanied by changes in gene expression within days. Together, the data suggest that inappropriate expression of CIZ1 AD fragments could drive epigenetic instability in early stage breast cancers by destabilizing the CIZ1 SMACs that normally protect repressed chromatin.