CDK1 controls CHMP7-dependent nuclear envelope reformation.

Alberto T Gatta,Peter B Rosenthal,Qu Chen,Yolanda Olmos,Caroline L Stoten,Jeremy G Carlton

doi:10.7554/elife.59999

Alberto T Gatta, Peter B Rosenthal + Show 4 more

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https://doi.org/10.7554/elife.59999

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Journal: eLife	Publication Date: Jul 21, 2021
Citations: 22	License type: CC BY 4.0

Affiliation: King's College London, The Francis Crick Institute

Abstract

Through membrane sealing and disassembly of spindle microtubules, the Endosomal Sorting Complex Required for Transport-III (ESCRT-III) machinery has emerged as a key player in the regeneration of a sealed nuclear envelope (NE) during mitotic exit, and in the repair of this organelle during interphase rupture. ESCRT-III assembly at the NE occurs transiently during mitotic (M) exit and is initiated when CHMP7, an ER-localised ESCRT-II/ESCRT-III hybrid protein, interacts with the Inner Nuclear Membrane (INM) protein LEM2. Whilst classical nucleocytoplasmic transport mechanisms have been proposed to separate LEM2 and CHMP7 during interphase, it is unclear how CHMP7 assembly is suppressed in mitosis when NE and ER identities are mixed. Here, we use live cell imaging and protein biochemistry to examine the biology of these proteins during M-exit. Firstly, we show that CHMP7 plays an important role in the dissolution of LEM2 clusters that form at the NE during M-exit. Secondly, we show that CDK1 phosphorylates CHMP7 upon M-entry at Ser3 and Ser441 and that this phosphorylation reduces CHMP7's interaction with LEM2, limiting its assembly during M-phase. We show that spatiotemporal differences in the dephosphorylation of CHMP7 license its assembly at the NE during telophase, but restrict its assembly on the ER at this time. Without CDK1 phosphorylation, CHMP7 undergoes inappropriate assembly in the peripheral ER during M-exit, capturing LEM2 and downstream ESCRT-III components. Lastly, we establish that a microtubule network is dispensable for ESCRT-III assembly at the reforming nuclear envelope. These data identify a key cell-cycle control programme allowing ESCRT-III-dependent nuclear regeneration.

Highlights

During division, cells undergo a programmed reorganisation of their interphase architecture to allow cyto- and karyokinesis
CHMP7 is required for dissolution of LEM2 clusters that form during nuclear envelope regeneration CHMP7 and LEM2 exhibit complex domain architectures (Figure 1A) and in interphase are localised to the Endoplasmic Reticulum (ER) and the Inner Nuclear Membrane (INM) respectively
We found that during mitotic exit, the INM protein LEM2 was co-enriched with CHMP7 at the reforming nuclear envelope and released in a CHMP7-dependent manner to populate the INM

Summary

Introduction

Cells undergo a programmed reorganisation of their interphase architecture to allow cyto- and karyokinesis. Membranes from the ER/NE hybrid organelle envelope nascent daughter nuclei, INM proteins recover their NE localisation, spindle microtubules traversing the NE are disassembled and remaining holes in the NE are sealed[2]. In addition to its roles in membrane trafficking and cytokinesis [3], ESCRT-III has emerged as a key orchestrator of nuclear envelope sealing during open mitosis [4,5,6,7], the repair of ruptured micro- and parental nuclear envelopes in interphase [8,9,10,11,12] and the surveillance of damaged NPC complexes in S. cerevisiae [13,14]. In the context of NE reformation, during M-exit, the inner nuclear membrane protein LEM2 assembles into a phase-separated gellike polymer that defines sites of ESCRT-dependent nuclear envelope sealing through its ability to recruit and activate polymerisation of the ER-localised ESCRT-III protein, CHMP7 [7,15]. Given the key role for LEM2 in stimulating CHMP7 polymerisation during M-exit, we wondered how the biology of CHMP7 and LEM2 was controlled during M-phase

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Conclusion