Abstract 1972: A novel signaling pathway delays abscission in cytokinesis with chromatin bridges

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Abstract Chromatin bridges are strands of missegregated chromatin connecting the anaphase poles or daughter nuclei and have been linked to tumourigenesis. In response to chromatin bridges in cytokinesis, cells delay abscission, the severing of the narrow cytoplasmic canal that connects the two daughter cells, to prevent chromatin breakage or tetraploiudization that are associated with genomic instability and cancer predisposition. In mammalian cells, this abscission delay is called “the abscission checkpoint” and is dependent on the localization and catalytic activity of the Chromosomal Passenger Complex (CPC) at the midbody. The CPC comprises the catalytic subunit Aurora B kinase, the scaffolding protein INCENP and the non-enzymatic subunits Survivin and Borealin; however, the molecular mechanisms that signal chromatin bridges to the CPC have not been previously identified. In the present study, we show that inhibition of the DNA damage kinases ATM or Chk2 impairs CPC-localization to the midbody and correlates with premature abscission and chromatin breakage in cytokinesis with trapped chromatin in human carcinoma cell lines. ATM phosphorylates Chk2-threonine 68 (T68) to activate Chk2 at the midbody. In turn, active Chk2 phosphorylates INCENP at the newly identified site serine 91 (S91) to promote CPC-localization to the midbody, to delay abscission and prevent chromatin breakage. Expression of siRNA-resistant phosphomimetic mutant INCENP-S91D or GFP:INCENP(FB) that is constitutively targeted to the Flemming body (FB), but not WT INCENP, rescues CPC-midbody-localization and prevents chromatin breakage in Chk2-deficient or ATM-deficient cells. In contrast, in the absence of the endogenous INCENP, the non-phosphorylatable mutant INCENP-S91A does not localize to the midbody and its expression promotes chromatin breakage. Furthermore, the Mre11-Rad50-Nbs1 (MRN) complex is required for ATM activation at the midbody. These results identify an MRN-ATM-Chk2-INCENP signaling pathway that prevents chromosome breakage in cytokinesis with chromatin bridges, by promoting CPC-midbody localization. Citation Format: Eleni Petsalaki, George Zachos. A novel signaling pathway delays abscission in cytokinesis with chromatin bridges [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1972.