scholarly journals Junctophilins: Key Membrane Tethers in Muscles and Neurons

2021 ◽  
Vol 14 ◽  
Author(s):  
Christopher A. Piggott ◽  
Yishi Jin
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Calcium Signaling ◽  
Deep Understanding ◽  
Evolutionary Conservation ◽  
Excitable Cells ◽  
Contraction Coupling ◽  
Functional Studies ◽  
Store Operated Calcium Entry ◽  
Membrane Tethers

Contacts between the endoplasmic reticulum (ER) and plasma membrane (PM) contain specialized tethering proteins that bind both ER and PM membranes. In excitable cells, ER–PM contacts play an important role in calcium signaling and transferring lipids. Junctophilins are a conserved family of ER–PM tethering proteins. They are predominantly expressed in muscles and neurons and known to simultaneously bind both ER- and PM-localized ion channels. Since their discovery two decades ago, functional studies using junctophilin-deficient animals have provided a deep understanding of their roles in muscles and neurons, including excitation-contraction coupling, store-operated calcium entry (SOCE), and afterhyperpolarization (AHP). In this review, we highlight key findings from mouse, fly, and worm that support evolutionary conservation of junctophilins.

scholarly journals Junctophilin-4, a component of the endoplasmic reticulum–plasma membrane junctions, regulates Ca2+ dynamics in T cells

2016 ◽  
Vol 113 (10) ◽  
pp. 2762-2767 ◽  
Author(s):  
Jin Seok Woo ◽  
Sonal Srikanth ◽  
Miyuki Nishi ◽  
Peipei Ping ◽  
Hiroshi Takeshima ◽  
...  
Keyword(s):  
T Cells ◽  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Genetic Manipulation ◽  
Erk Signaling ◽  
Excitable Cells ◽  
Activated T Cells ◽  
Activation Markers ◽  
Extracellular Signaling ◽  
Store Depletion

Orai1 and stromal interaction molecule 1 (STIM1) mediate store-operated Ca2+ entry (SOCE) in immune cells. STIM1, an endoplasmic reticulum (ER) Ca2+ sensor, detects store depletion and interacts with plasma membrane (PM)-resident Orai1 channels at the ER–PM junctions. However, the molecular composition of these junctions in T cells remains poorly understood. Here, we show that junctophilin-4 (JP4), a member of junctional proteins in excitable cells, is expressed in T cells and localized at the ER–PM junctions to regulate Ca2+ signaling. Silencing or genetic manipulation of JP4 decreased ER Ca2+ content and SOCE in T cells, impaired activation of the nuclear factor of activated T cells (NFAT) and extracellular signaling-related kinase (ERK) signaling pathways, and diminished expression of activation markers and cytokines. Mechanistically, JP4 directly interacted with STIM1 via its cytoplasmic domain and facilitated its recruitment into the junctions. Accordingly, expression of this cytoplasmic fragment of JP4 inhibited SOCE. Furthermore, JP4 also formed a complex with junctate, a Ca2+-sensing ER-resident protein, previously shown to mediate STIM1 recruitment into the junctions. We propose that the junctate–JP4 complex located at the junctions cooperatively interacts with STIM1 to maintain ER Ca2+ homeostasis and mediate SOCE in T cells.

scholarly journals Rotavirus Calcium Dysregulation Manifests as Dynamic Calcium Signaling in the Cytoplasm and Endoplasmic Reticulum

2019 ◽  
Author(s):  
Alexandra L. Chang-Graham ◽  
Jacob L. Perry ◽  
Alicia C. Strtak ◽  
Nina K. Ramachandran ◽  
Jeanette M. Criglar ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Calcium Signaling ◽  
Calcium Homeostasis ◽  
Calcium Release ◽  
Nonstructural Protein ◽  
Time Lapse ◽  
Cytosolic Calcium ◽  
New Paradigm ◽  
Temporal Complexity ◽  
Store Operated Calcium Entry

AbstractLike many viruses, rotavirus (RV) dysregulates calcium homeostasis by elevating cytosolic calcium ([Ca2+]cyt) and decreasing endoplasmic reticulum (ER) stores. While an overall, monophasic increase in [Ca2+]cyt during RV infection has been shown, the nature of the RV-induced aberrant calcium signals and how they manifest over time at the single-cell level have not been characterized. Thus, we generated cell lines and human intestinal enteroids (HIEs) stably expressing cytosolic and/or ER-targeted genetically-encoded calcium indicators to characterize calcium signaling throughout RV infection by time-lapse imaging. We found that RV induces highly dynamic [Ca2+]cyt signaling that manifest as hundreds of discrete [Ca2+]cyt spikes, which increase during peak infection. Knockdown of nonstructural protein 4 (NSP4) attenuates the [Ca2+]cyt spikes, consistent with its role in dysregulating calcium homeostasis. RV-induced [Ca2+]cyt spikes were primarily from ER calcium release and were attenuated by inhibiting the store-operated calcium entry (SOCE) channel Orai1. RV-infected HIEs also exhibited prominent [Ca2+]cyt spikes that were attenuated by inhibiting SOCE, underlining the relevance of these [Ca2+]cyt spikes to gastrointestinal physiology and role of SOCE in RV pathophysiology. Thus, our discovery that RV increases [Ca2+]cyt by dynamic Ca2+signaling, establishes a new, paradigm-shifting understanding of the spatial and temporal complexity of virus-induced Ca2+signaling.

scholarly journals Structures reveal opening of the store-operated calcium channel Orai

2018 ◽  
Author(s):  
Xiaowei Hou ◽  
Shana R. Burstein ◽  
Stephen B. Long
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Ion Permeation ◽  
Excitable Cells ◽  
Gain Of Function ◽  
X Ray ◽  
Open Conformation ◽  
Density Maps ◽  
Cytosolic Side ◽  
Closed Pore

AbstractThe store-operated calcium (Ca2+) channel Orai governs Ca2+ influx through the plasma membrane of many non-excitable cells in metazoans. The channel opens in response to depletion of Ca2+ within the endoplasmic reticulum (ER). Loss- and gain-of-function mutants of Orai cause disease. Our previous work revealed the structure of Orai with a closed pore. Here, using a gain-of-function mutation that constitutively activates the channel, we present an X-ray structure of Drosophila melanogaster Orai in an open conformation. Well-defined electron density maps reveal that the open pore is dramatically dilated on its cytosolic side in comparison to the slender closed pore. Cations and anions bind in different regions of the open pore, informing mechanisms for ion permeation and the exquisite selectivity of the channel for Ca2+. Opening of the pore requires the release of cytosolic latches. Together with additional X-ray structures of an unlatched-but-closed intermediate, we propose a sequence for store-operated activation.

Triple Fixation For Electron Microscopy

1968 ◽  
Vol 26 ◽  
pp. 90-91 ◽  
Author(s):  
M. A. Hayat
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Electron Beam ◽  
Plasma Membrane ◽  
Myelin Sheath ◽  
Good Deal ◽  
Granular Structure ◽  
Oxidizing Agent ◽  
Fixation Technique ◽  
Large Clusters

Potassium permanganate has been successfully employed to study membranous structures such as endoplasmic reticulum, Golgi, plastids, plasma membrane and myelin sheath. Since KMnO4 is a strong oxidizing agent, deposition of manganese or its oxides account for some of the observed contrast in the lipoprotein membranes, but a good deal of it is due to the removal of background proteins either by dehydration agents or by volatalization under the electron beam. Tissues fixed with KMnO4 exhibit somewhat granular structure because of the deposition of large clusters of stain molecules. The gross arrangement of membranes can also be modified. Since the aim of a good fixation technique is to preserve satisfactorily the cell as a whole and not the best preservation of only a small part of it, a combination of a mixture of glutaraldehyde and acrolein to obtain general preservation and KMnO4 to enhance contrast was employed to fix plant embryos, green algae and fungi.

scholarly journals Synaptotagmins at the endoplasmic reticulum–plasma membrane contact sites maintain diacylglycerol homeostasis during abiotic stress

2021 ◽  
Author(s):  
Noemi Ruiz-Lopez ◽  
Jessica Pérez-Sancho ◽  
Alicia Esteban del Valle ◽  
Richard P Haslam ◽  
Steffen Vanneste ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Abiotic Stress ◽  
Fluorescent Protein ◽  
Mechanical Damage ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Green Fluorescent

Abstract Endoplasmic reticulum-plasma membrane contact sites (ER-PM CS) play fundamental roles in all eukaryotic cells. Arabidopsis thaliana mutants lacking the ER-PM protein tether synaptotagmin1 (SYT1) exhibit decreased plasma membrane (PM) integrity under multiple abiotic stresses such as freezing, high salt, osmotic stress and mechanical damage. Here, we show that, together with SYT1, the stress-induced SYT3 is an ER-PM tether that also functions in maintaining PM integrity. The ER-PM CS localization of SYT1 and SYT3 is dependent on PM phosphatidylinositol-4-phosphate and is regulated by abiotic stress. Lipidomic analysis revealed that cold stress increased the accumulation of diacylglycerol at the PM in a syt1/3 double mutant relative to wild type while the levels of most glycerolipid species remain unchanged. Additionally, the SYT1-green fluorescent protein (GFP) fusion preferentially binds diacylglycerol in vivo with little affinity for polar glycerolipids. Our work uncovers a SYT-dependent mechanism of stress adaptation counteracting the detrimental accumulation of diacylglycerol at the PM produced during episodes of abiotic stress.

scholarly journals Synthesis and Characterization of Store-Operated Calcium Entry Inhibitors Active in the Submicromolar Range

2020 ◽  
Vol 21 (24) ◽  
pp. 9777
Author(s):  
Camille Le Guilcher ◽  
Tomas Luyten ◽  
Jan B. Parys ◽  
Mathieu Pucheault ◽  
Olivier Dellis
Keyword(s):  
Cell Activation ◽  
Interleukin 2 ◽  
Calcium Entry ◽  
Ip3 Receptors ◽  
Excitable Cells ◽  
Cellular Targets ◽  
Entry Inhibitors ◽  
The Past ◽  
Store Operated Calcium Entry

The store-operated calcium entry, better known as SOCE, forms the main Ca2+ influx pathway in non-excitable cells, especially in leukocytes, where it is required for cell activation and the immune response. During the past decades, several inhibitors were developed, but they lack specificity or efficacy. From the non-specific SOCE inhibitor 2-aminoethyl diphenylborinate (2-APB), we synthetized 16 new analogues by replacing/modifying the phenyl groups. Among them, our compound P11 showed the best inhibitory capacity with a Ki ≈ 75 nM. Furthermore, below 1 µM, P11 was devoid of any inhibitory activity on the two other main cellular targets of 2-APB, the IP3 receptors, and the SERCA pumps. Interestingly, Jurkat T cells secrete interleukin-2 under phytohemagglutinin stimulation but undergo cell death and stop IL-2 synthesis when stimulated in the presence of increasing P11 concentrations. Thus, P11 could represent the first member of a new and potent family of immunosuppressors.

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