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Tiffner A, Hopl V, Derler I. CRAC and SK Channels: Their Molecular Mechanisms Associated with Cancer Cell Development. Cancers (Basel) 2022; 15:cancers15010101. [PMID: 36612099 PMCID: PMC9817886 DOI: 10.3390/cancers15010101] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 12/16/2022] [Accepted: 12/19/2022] [Indexed: 12/28/2022] Open
Abstract
Cancer represents a major health burden worldwide. Several molecular targets have been discovered alongside treatments with positive clinical outcomes. However, the reoccurrence of cancer due to therapy resistance remains the primary cause of mortality. Endeavors in pinpointing new markers as molecular targets in cancer therapy are highly desired. The significance of the co-regulation of Ca2+-permeating and Ca2+-regulated ion channels in cancer cell development, proliferation, and migration make them promising molecular targets in cancer therapy. In particular, the co-regulation of the Orai1 and SK3 channels has been well-studied in breast and colon cancer cells, where it finally leads to an invasion-metastasis cascade. Nevertheless, many questions remain unanswered, such as which key molecular components determine and regulate their interplay. To provide a solid foundation for a better understanding of this ion channel co-regulation in cancer, we first shed light on the physiological role of Ca2+ and how this ion is linked to carcinogenesis. Then, we highlight the structure/function relationship of Orai1 and SK3, both individually and in concert, their role in the development of different types of cancer, and aspects that are not yet known in this context.
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2
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Tiffner A, Derler I. Isoform-Specific Properties of Orai Homologues in Activation, Downstream Signaling, Physiology and Pathophysiology. Int J Mol Sci 2021; 22:8020. [PMID: 34360783 PMCID: PMC8347056 DOI: 10.3390/ijms22158020] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 07/21/2021] [Accepted: 07/23/2021] [Indexed: 11/21/2022] Open
Abstract
Ca2+ ion channels are critical in a variety of physiological events, including cell growth, differentiation, gene transcription and apoptosis. One such essential entry pathway for calcium into the cell is the Ca2+ release-activated Ca2+ (CRAC) channel. It consists of the Ca2+ sensing protein, stromal interaction molecule 1 (STIM1) located in the endoplasmic reticulum (ER) and a Ca2+ ion channel Orai in the plasma membrane. The Orai channel family includes three homologues Orai1, Orai2 and Orai3. While Orai1 is the "classical" Ca2+ ion channel within the CRAC channel complex and plays a universal role in the human body, there is increasing evidence that Orai2 and Orai3 are important in specific physiological and pathophysiological processes. This makes them an attractive target in drug discovery, but requires a detailed understanding of the three Orai channels and, in particular, their differences. Orai channel activation is initiated via Ca2+ store depletion, which is sensed by STIM1 proteins, and induces their conformational change and oligomerization. Upon STIM1 coupling, Orai channels activate to allow Ca2+ permeation into the cell. While this activation mechanism is comparable among the isoforms, they differ by a number of functional and structural properties due to non-conserved regions in their sequences. In this review, we summarize the knowledge as well as open questions in our current understanding of the three isoforms in terms of their structure/function relationship, downstream signaling and physiology as well as pathophysiology.
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Affiliation(s)
| | - Isabella Derler
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, A-4020 Linz, Austria;
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3
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The Orai Pore Opening Mechanism. Int J Mol Sci 2021; 22:ijms22020533. [PMID: 33430308 PMCID: PMC7825772 DOI: 10.3390/ijms22020533] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2020] [Revised: 12/30/2020] [Accepted: 01/02/2021] [Indexed: 02/07/2023] Open
Abstract
Cell survival and normal cell function require a highly coordinated and precise regulation of basal cytosolic Ca2+ concentrations. The primary source of Ca2+ entry into the cell is mediated by the Ca2+ release-activated Ca2+ (CRAC) channel. Its action is stimulated in response to internal Ca2+ store depletion. The fundamental constituents of CRAC channels are the Ca2+ sensor, stromal interaction molecule 1 (STIM1) anchored in the endoplasmic reticulum, and a highly Ca2+-selective pore-forming subunit Orai1 in the plasma membrane. The precise nature of the Orai1 pore opening is currently a topic of intensive research. This review describes how Orai1 gating checkpoints in the middle and cytosolic extended transmembrane regions act together in a concerted manner to ensure an opening-permissive Orai1 channel conformation. In this context, we highlight the effects of the currently known multitude of Orai1 mutations, which led to the identification of a series of gating checkpoints and the determination of their role in diverse steps of the Orai1 activation cascade. The synergistic action of these gating checkpoints maintains an intact pore geometry, settles STIM1 coupling, and governs pore opening. We describe the current knowledge on Orai1 channel gating mechanisms and summarize still open questions of the STIM1-Orai1 machinery.
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Tiffner A, Schober R, Höglinger C, Bonhenry D, Pandey S, Lunz V, Sallinger M, Frischauf I, Fahrner M, Lindinger S, Maltan L, Berlansky S, Stadlbauer M, Schindl R, Ettrich R, Romanin C, Derler I. CRAC channel opening is determined by a series of Orai1 gating checkpoints in the transmembrane and cytosolic regions. J Biol Chem 2021; 296:100224. [PMID: 33361160 PMCID: PMC7948504 DOI: 10.1074/jbc.ra120.015548] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 12/15/2020] [Accepted: 12/22/2020] [Indexed: 12/13/2022] Open
Abstract
The initial activation step in the gating of ubiquitously expressed Orai1 calcium (Ca2+) ion channels represents the activation of the Ca2+-sensor protein STIM1 upon Ca2+ store depletion of the endoplasmic reticulum. Previous studies using constitutively active Orai1 mutants gave rise to, but did not directly test, the hypothesis that STIM1-mediated Orai1 pore opening is accompanied by a global conformational change of all Orai transmembrane domain (TM) helices within the channel complex. We prove that a local conformational change spreads omnidirectionally within the Orai1 complex. Our results demonstrate that these locally induced global, opening-permissive TM motions are indispensable for pore opening and require clearance of a series of Orai1 gating checkpoints. We discovered these gating checkpoints in the middle and cytosolic extended TM domain regions. Our findings are based on a library of double point mutants that contain each one loss-of-function with one gain-of-function point mutation in a series of possible combinations. We demonstrated that an array of loss-of-function mutations are dominant over most gain-of-function mutations within the same as well as of an adjacent Orai subunit. We further identified inter- and intramolecular salt-bridge interactions of Orai subunits as a core element of an opening-permissive Orai channel architecture. Collectively, clearance and synergistic action of all these gating checkpoints are required to allow STIM1 coupling and Orai1 pore opening. Our results unravel novel insights in the preconditions of the unique fingerprint of CRAC channel activation, provide a valuable source for future structural resolutions, and help to understand the molecular basis of disease-causing mutations.
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Affiliation(s)
- Adéla Tiffner
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Romana Schober
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Carmen Höglinger
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Daniel Bonhenry
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Czech Academy of Sciences, Nove Hrady, Czechia
| | - Saurabh Pandey
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Czech Academy of Sciences, Nove Hrady, Czechia
| | - Victoria Lunz
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Matthias Sallinger
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Irene Frischauf
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Marc Fahrner
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Sonja Lindinger
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Lena Maltan
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Sascha Berlansky
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Michael Stadlbauer
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Rainer Schindl
- Gottfried Schatz Research Center, Medical University of Graz, Graz, Austria
| | - Rudiger Ettrich
- College of Biomedical Sciences, Larkin University, Miami, Florida, USA; Faculty of Mathematics and Physics, Charles University, Prague, Czechia; Department of Cellular Biology & Pharmacology, Herbert Wertheim College of Medicine, Florida International University, Miami, Florida, USA
| | - Christoph Romanin
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria
| | - Isabella Derler
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz, Austria.
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Tiffner A, Derler I. Molecular Choreography and Structure of Ca 2+ Release-Activated Ca 2+ (CRAC) and K Ca2+ Channels and Their Relevance in Disease with Special Focus on Cancer. MEMBRANES 2020; 10:E425. [PMID: 33333945 PMCID: PMC7765462 DOI: 10.3390/membranes10120425] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Revised: 12/04/2020] [Accepted: 12/07/2020] [Indexed: 12/16/2022]
Abstract
Ca2+ ions play a variety of roles in the human body as well as within a single cell. Cellular Ca2+ signal transduction processes are governed by Ca2+ sensing and Ca2+ transporting proteins. In this review, we discuss the Ca2+ and the Ca2+-sensing ion channels with particular focus on the structure-function relationship of the Ca2+ release-activated Ca2+ (CRAC) ion channel, the Ca2+-activated K+ (KCa2+) ion channels, and their modulation via other cellular components. Moreover, we highlight their roles in healthy signaling processes as well as in disease with a special focus on cancer. As KCa2+ channels are activated via elevations of intracellular Ca2+ levels, we summarize the current knowledge on the action mechanisms of the interplay of CRAC and KCa2+ ion channels and their role in cancer cell development.
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Affiliation(s)
| | - Isabella Derler
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, A-4020 Linz, Austria;
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Niu L, Wu F, Li K, Li J, Zhang SL, Hu J, Wang Q. STIM1 interacts with termini of Orai channels in a sequential manner. J Cell Sci 2020; 133:jcs239491. [PMID: 32107289 DOI: 10.1242/jcs.239491] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 02/24/2020] [Indexed: 12/20/2022] Open
Abstract
Store-operated Ca2+ entry (SOCE) is critical for numerous Ca2+-related processes. The activation of SOCE requires engagement between stromal interaction molecule 1 (STIM1) molecules on the endoplasmic reticulum and Ca2+ release-activated channel (CRAC) Orai on the plasma membrane. However, the molecular details of their interactions remain elusive. Here, we analyzed STIM1-Orai interactions using synthetic peptides derived from the N- and C-termini of Orai channels (Orai-NT and Orai-CT, respectively) and purified fragments of STIM1. The binding of STIM1 to Orai-NT is hydrophilic based, whereas binding to the Orai-CT is mostly hydrophobic. STIM1 decreases its affinity for Orai-CT when Orai-NT is present, supporting a stepwise interaction. Orai3-CT exhibits stronger binding to STIM1 than Orai1-CT, largely due to the shortness of one helical turn. The role of newly identified residues was confirmed by co-immunoprecipitation and Ca2+ imaging using full-length molecules. Our results provide important insight into CRAC gating by STIM1.
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Affiliation(s)
- Liling Niu
- Department of Immunology, School of Basic Medical Sciences, Tianjin Medical University, and Tianjin Key Laboratory of Cellular and Molecular Immunology, Tianjin 300070, China
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Fuyun Wu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China
- School of Basic Medical Sciences, Hubei University of Medicine, Shiyan 442000, China
| | - Kaili Li
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Jing Li
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Shenyuan L Zhang
- Department of Medical Physiology, College of Medicine, Texas A&M Health Science Center, Temple, TX 76504, USA
| | - Junjie Hu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Qian Wang
- Department of Immunology, School of Basic Medical Sciences, Tianjin Medical University, and Tianjin Key Laboratory of Cellular and Molecular Immunology, Tianjin 300070, China
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Yeung PSW, Yamashita M, Prakriya M. Molecular basis of allosteric Orai1 channel activation by STIM1. J Physiol 2019; 598:1707-1723. [PMID: 30950063 DOI: 10.1113/jp276550] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Accepted: 03/19/2019] [Indexed: 12/13/2022] Open
Abstract
Store-operated Ca2+ entry through Orai1 channels is a primary mechanism for Ca2+ entry in many cells and mediates numerous cellular effector functions ranging from gene transcription to exocytosis. Orai1 channels are amongst the most Ca2+ -selective channels known and are activated by direct physical interactions with the endoplasmic reticulum Ca2+ sensor stromal interaction molecule 1 (STIM1) in response to store depletion triggered by stimulation of a variety of cell surface G-protein coupled and tyrosine kinase receptors. Work in the last decade has revealed that the Orai1 gating process is highly cooperative and strongly allosteric, likely driven by a wave of interdependent conformational changes throughout the protein originating in the peripheral C-terminal ligand binding site and culminating in pore opening. In this review, we survey the structural and molecular features in Orai1 that contribute to channel gating and consider how they give rise to the unique biophysical fingerprint of Orai1 currents.
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Affiliation(s)
- Priscilla See-Wai Yeung
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Megumi Yamashita
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Murali Prakriya
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
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