Securin-independent regulation of separase by checkpoint-induced shugoshin-MAD2

• Published in: Nature (London) Vol. 580; no. 7804; pp. 536 - 541
• Main Authors: Hellmuth, Susanne, Gómez-H, Laura, Pendás, Alberto M, Stemmann, Olaf
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 23.04.2020
• Subjects: Adenosine triphosphatase; Analysis; Anaphase; Anaphase-promoting complex; Anaphase-Promoting Complex-Cyclosome - metabolism; ATPases Associated with Diverse Cellular Activities - metabolism; Cdc20 Proteins - metabolism; Cell cycle; Cell Cycle Checkpoints - physiology; Cell Cycle Proteins - metabolism; Cell Line; Chromatids; Chromatids - metabolism; Chromosomal Proteins, Non-Histone - metabolism; Chromosomes; Cohesin; Cohesins; Cohesion; Control; Cysteine proteinases; Cytotoxicity; Deregulation; Humans; Influence; Inhibitors; Mad2 Proteins - metabolism; Meiosis; Metaphase; Proteasomes; Protectors; Protein Binding; Proteins; Schedules; Securin; Securin - metabolism; Separase; Separase - antagonists & inhibitors; Separase - metabolism; Separation; Sister chromatids; Substrate inhibition; Toxicity; Ubiquitin; Ubiquitin-protein ligase; Germany
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-020-2182-3

Separation of eukaryotic sister chromatids during the cell cycle is timed by the spindle assembly checkpoint (SAC) and ultimately triggered when separase cleaves cohesion-mediating cohesin . Silencing of the SAC during metaphase activates the ubiquitin ligase APC/C (anaphase-promoting complex, also known as the cyclosome) and results in the proteasomal destruction of the separase inhibitor securin . In the absence of securin, mammalian chromosomes still segregate on schedule, but it is unclear how separase is regulated under these conditions . Here we show that human shugoshin 2 (SGO2), an essential protector of meiotic cohesin with unknown functions in the soma , is turned into a separase inhibitor upon association with SAC-activated MAD2. SGO2-MAD2 can functionally replace securin and sequesters most separase in securin-knockout cells. Acute loss of securin and SGO2, but not of either protein individually, resulted in separase deregulation associated with premature cohesin cleavage and cytotoxicity. Similar to securin , SGO2 is a competitive inhibitor that uses a pseudo-substrate sequence to block the active site of separase. APC/C-dependent ubiquitylation and action of the AAA-ATPase TRIP13 in conjunction with the MAD2-specific adaptor p31 liberate separase from SGO2-MAD2 in vitro. The latter mechanism facilitates a considerable degree of sister chromatid separation in securin-knockout cells that lack APC/C activity. Thus, our results identify an unexpected function of SGO2 in mitotically dividing cells and a mechanism of separase regulation that is independent of securin but still supervised by the SAC.