Remodeling of ER–plasma membrane contact sites but not STIM1 phosphorylation inhibits Ca ²⁺ influx in mitosis

Abstract

Store-operated Ca2+ entry (SOCE), mediated by the endoplasmic reticulum (ER) Ca2+ sensor stromal interaction molecule 1 (STIM1) and the plasma membrane (PM) channel Orai1, is inhibited during mitosis. STIM1 phosphorylation has been suggested to mediate this inhibition, but it is unclear whether additional pathways are involved. Here, we demonstrate using various approaches, including a nonphosphorylatable STIM1 knock-in mouse, that STIM1 phosphorylation is not required for SOCE inhibition in mitosis. Rather, multiple pathways converge to inhibit Ca2+ influx in mitosis. STIM1 interacts with the cochaperone BAG3 and localizes to autophagosomes in mitosis, and STIM1 protein levels are reduced. The density of ER–PM contact sites (CSs) is also dramatically reduced in mitosis, thus physically preventing STIM1 and Orai1 from interacting to activate SOCE. Our findings provide insights into ER–PM CS remodeling during mitosis and a mechanistic explanation of the inhibition of Ca2+ influx that is required for cell cycle progression.

Ca2+ Release by IP3 Receptors Is Required to Orient the Mitotic Spindle

“…Progression through the cell cycle is controlled by regulated degradation of cyclins, but local Ca 2+ signals are also important at critical stages ( Keith et al., 1985 ; Parry et al., 2005 ; Zhao et al., 2019 ), including nuclear envelope breakdown, the transition from metaphase to anaphase and cytokinesis. The mechanisms are largely unresolved, but because store-operated Ca 2+ entry is inhibited during meiosis and mitosis ( Smyth and Putney, 2012 ; Yu et al., 2019 ), the Ca 2+ signals are probably evoked by IP 3 Rs. We have shown that cells can proliferate without IP 3 Rs ( Figure S1 A) ( Alzayady et al., 2016 ; Ando et al., 2018 ; Atakpa et al., 2019 ; Sugawara et al., 1997 ), but their behavior is compromised.…”

“…Ca 2+ signals typically arise from a combination of Ca 2+ release from intracellular stores, predominantly within the endoplasmic reticulum (ER), and Ca 2+ entry across the plasma membrane. Store-operated Ca 2+ entry, where loss of Ca 2+ from the ER triggers opening of Ca 2+ channels in the plasma membrane, is the most widely expressed Ca 2+ entry pathway, but it is completely inhibited during mitosis ( Smyth et al., 2009 ; Yu et al., 2019 ). Hence, mitotic Ca 2+ signals are likely to be due entirely to release of Ca 2+ from intracellular stores ( Ciapa et al., 1994 ), most likely mediated by opening of inositol 1,4,5-trisphosphate receptors (IP 3 Rs), which are ubiquitously expressed intracellular Ca 2+ channels ( Rossi and Taylor, 2018 ).…”

The carboxy terminal coiled-coil modulates Orai1 internalization during meiosis

“…Of note, Orai1 internalization appears to be specific to oocyte meiosis 9 , 10 , 33 and is not observed during mitosis 34 . Furthermore, during interphase Orai1 recycles continuously with rapid kinetics at the PM and its membrane residence is modulated by Ca 2+ store content as well interaction with the CCT chaperonin complex 7 , 8 .…”

Organelle Inheritance Control of Mitotic Entry and Progression: Implications for Tissue Homeostasis and Disease

“…Considering its role as a major organizing compartment, it is likely that the inheritance of the ER is regulated by yet unknown control mechanisms. Recently, it has been shown that the ER–PM CSs undergo significant changes in morphology and function during mitosis (Yu et al, 2019). One of the major functions of CSs is to control Ca 2+ signaling through the store-operated Ca 2+ entry (SOCE), which depends on the integrity of ER–PM CS to allow contact between the proteins STIM1 and Orai1 (Yu et al, 2019).…”

“…Therefore, the down-regulation of ER–PM junctions in mitosis induces SOCE inhibition by preventing the interaction of STIM1 with Orai1. This inhibition could affect not only Ca 2+ signaling but also lipid metabolism and membrane structure (Yu et al, 2019).…”