Abstract 1589: Unraveling the mechanisms underlying micronuclear rupture, a seminal event in cancer progression

Abstract Chromosomal instability is a hallmark of aggressive human cancers and it is often associated with metastasis, immune evasion, and therapeutic resistance. Chromosomally unstable tumors often contain rupture-prone micronuclei, which harbor mis-segregated chromosomes. Rupture of micronuclear envelopes represents a critical event in the evolution of chromosomally unstable tumors given its ability to catalyze the formation of genomic rearrangements known as chromothripsis, and to trigger the cytosolic DNA-sensing cGAS-STING inflammatory pathway, whose aberrant and chronic activation was found to promote metastatic progression [1]. Despite its central role in tumor progression, how micronuclear membranes collapse and why membrane repair mechanisms, which are functional at the primary nucleus, fail to restore micronuclear integrity, remains poorly understood. Here we show that the answer to these fundamental questions lays in mitochondria proximity to micronuclei: by means of advanced microscopy and cellular and molecular biology techniques, our results demonstrate that ruptured micronuclei are more heavily embedded in the mitochondrial matrix than the intact ones, and that ROS are the main cause of micronuclear rupture. We used a combination of ROS-inducing drugs on a variety of cell lines to show an increase in collapsed micronuclei, while using ROS-scavengers we reduced the physiological basal amount of micronuclear rupture. Nuclear membrane catastrophe has recently been identified as the main outcome of unrestrained activity of the ESCRT-III nuclear membrane repair complex, of which CHMP7 is the scaffolding protein [2]. We showed that cells under oxidative stress display an increase in CHMP7 content in micronuclei whose membrane is not yet collapsed, implicating a causative role of CHMP7 in micronuclear envelope rupture. Furthermore, by means of genetic manipulation we demonstrate a central role for CHMP7 in ROS-induced rupture, with evidences pointing towards a non-canonical role for CHMP7 in this process. We thus provide a mechanistic insight into a fundamental hub in advanced cancers metastatic onset: by understanding the players involved into micronuclear collapse, this work can bring to light new untapped drug targets that are specific for those cells that will undergo metastatic transformation. In conclusion, our study has the potential to develop new and more effective therapies for the treatment of aggressive chromosomally unstable cancers. 1. Bakhoum, S.F., et al., Chromosomal instability drives metastasis through a cytosolic DNA response. Nature, 2018. 553(7689): p. 467-472. 2. Vietri, M., et al., Unrestrained ESCRT-III drives micronuclear catastrophe and chromosome fragmentation. Nat Cell Biol, 2020. 22(7): p. 856-867 Citation Format: Melody Di Bona, Albert Agustinus, Yanyang Chen, Lorenzo Scipioni, Daniel Bronder, Samuel F. Bakhoum. Unraveling the mechanisms underlying micronuclear rupture, a seminal event in cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1589.