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Oncomodulin (OCM) uniquely regulates calcium signaling in neonatal cochlear outer hair cells. Cell Calcium 2022; 105:102613. [PMID: 35797824 PMCID: PMC9297295 DOI: 10.1016/j.ceca.2022.102613] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Revised: 06/06/2022] [Accepted: 06/09/2022] [Indexed: 11/23/2022]
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2
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The Highly Conservative Cysteine of Oncomodulin as a Feasible Redox Sensor. Biomolecules 2021; 11:biom11010066. [PMID: 33419032 PMCID: PMC7825312 DOI: 10.3390/biom11010066] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 01/01/2021] [Accepted: 01/03/2021] [Indexed: 11/17/2022] Open
Abstract
Oncomodulin (Ocm), or parvalbumin β, is an 11-12 kDa Ca2+-binding protein found inside and outside of vertebrate cells, which regulates numerous processes via poorly understood mechanisms. Ocm consists of two active Ca2+-specific domains of the EF-hand type ("helix-loop-helix" motif), covered by an EF-hand domain with inactive EF-hand loop, which contains a highly conservative cysteine with unknown function. In this study, we have explored peculiarities of the microenvironment of the conservative Cys18 of recombinant rat Ocm (rWT Ocm), redox properties of this residue, and structural/functional sensitivity of rWT Ocm to the homologous C18S substitution. We have found that pKa
of the Cys18 thiol lays beyond the physiological pH range. The measurement of redox dependence of rWT Ocm thiol-disulfide equilibrium (glutathione redox pair) showed that redox potential of Cys18 for the metal-free and Ca2+-loaded protein is of -168 mV and -176 mV, respectively. Therefore, the conservative thiol of rWT Ocm is prone to disulfide dimerization under physiological redox conditions. The C18S substitution drastically reduces α-helices content of the metal-free and Mg2+-bound Ocm, increases solvent accessibility of its hydrophobic residues, eliminates the cooperative thermal transition in the apo-protein, suppresses Ca2+/Mg2+ affinity of the EF site, and accelerates Ca2+ dissociation from Ocm. The distinct structural and functional consequences of the minor structural modification of Cys18 indicate its possible redox sensory function. Since some other EF-hand proteins also contain a conservative redox-sensitive cysteine located in an inactive EF-hand loop, it is reasonable to suggest that in the course of evolution, some of the EF-hands attained redox sensitivity at the expense of the loss of their Ca2+ affinity.
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Schwaller B. Cytosolic Ca 2+ Buffers Are Inherently Ca 2+ Signal Modulators. Cold Spring Harb Perspect Biol 2020; 12:cshperspect.a035543. [PMID: 31308146 DOI: 10.1101/cshperspect.a035543] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
For precisely regulating intracellular Ca2+ signals in a time- and space-dependent manner, cells make use of various components of the "Ca2+ signaling toolkit," including Ca2+ entry and Ca2+ extrusion systems. A class of cytosolic Ca2+-binding proteins termed Ca2+ buffers serves as modulators of such, mostly short-lived Ca2+ signals. Prototypical Ca2+ buffers include parvalbumins (α and β isoforms), calbindin-D9k, calbindin-D28k, and calretinin. Although initially considered to function as pure Ca2+ buffers, that is, as intracellular Ca2+ signal modulators controlling the shape (amplitude, decay, spread) of Ca2+ signals, evidence has accumulated that calbindin-D28k and calretinin have additional Ca2+ sensor functions. These other functions are brought about by direct interactions with target proteins, thereby modulating their targets' function/activity. Dysregulation of Ca2+ buffer expression is associated with several neurologic/neurodevelopmental disorders including autism spectrum disorder (ASD) and schizophrenia. In some cases, the presence of these proteins is presumed to confer a neuroprotective effect, as evidenced in animal models of Parkinson's or Alzheimer's disease.
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Affiliation(s)
- Beat Schwaller
- Department of Anatomy, Section of Medicine, University of Fribourg, CH-1700 Fribourg, Switzerland
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Climer LK, Cox AM, Reynolds TJ, Simmons DD. Oncomodulin: The Enigmatic Parvalbumin Protein. Front Mol Neurosci 2019; 12:235. [PMID: 31649505 PMCID: PMC6794386 DOI: 10.3389/fnmol.2019.00235] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2019] [Accepted: 09/13/2019] [Indexed: 01/21/2023] Open
Abstract
EF-hand Ca2+-binding protein family members, α- and β-parvalbumins have been studied for decades. Yet, considerable information is lacking distinguishing functional differences between mammalian α-parvalbumin (PVALB) and oncomodulin (OCM), a branded β-parvalbumin. Herein, we provide an overview detailing the current body of work centered around OCM as an EF-Hand Ca2+-binding protein and describe potential mechanisms of OCM function within the inner ear and immune cells. Additionally, we posit that OCM is evolutionarily distinct from PVALB and most other β-parvalbumins. This review summarizes recent studies pertaining to the function of OCM and emphasizes OCM as a parvalbumin possessing a unique cell and tissue distribution, Ca2+ buffering capacity and phylogenetic origin.
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Affiliation(s)
- Leslie K Climer
- Department of Biology, Baylor University, Waco, TX, United States.,Department of Psychology and Neuroscience, Baylor University, Waco, TX, United States
| | - Andrew M Cox
- Department of Biology, Baylor University, Waco, TX, United States.,Department of Psychology and Neuroscience, Baylor University, Waco, TX, United States
| | | | - Dwayne D Simmons
- Department of Biology, Baylor University, Waco, TX, United States.,Department of Psychology and Neuroscience, Baylor University, Waco, TX, United States.,Biomedical Sciences Program, Baylor University, Waco, TX, United States
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Novak Kujundžić R, Steffens WL, Brewer JM, Henzl MT, Ragland WL. Characterization of avian thymic hormone and chicken parvalbumin 3 target cells. Int Immunopharmacol 2013; 15:282-8. [PMID: 23333630 DOI: 10.1016/j.intimp.2012.12.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Revised: 12/05/2012] [Accepted: 12/18/2012] [Indexed: 10/27/2022]
Abstract
Avian thymic hormone (ATH) is a β-parvalbumin produced by epithelial cells in the thymic cortex and in the eyes of chickens. Chicken parvalbumin 3 (CPV3) is a homologous protein produced in the thymus and in hair cells of the chicken ear. ATH circulates in the blood on a five-day cycle and stimulates cell-mediated immunity when administered to young chickens. We report the identification of target cells for ATH and CPV3 and the immunophenotype of target cells for ATH. Newly hatched chicks were injected intracoelomically with ATH and killed 5, 10, 15 or 20 min later. Naïve chickens also were killed at 1, 7 and 14 days of age. Various tissues were examined by EM for the presence of either ATH or CPV3 using colloidal gold labeling. Gold particles were initially present on plasma membranes of lymphocytes in T cell areas of spleen and cecal tonsils from the chicks injected with ATH, internalized within 10 min, and accumulated in nuclei by 20 min. Immunofluorescence staining also identified the presence of ATH in T cell areas of spleen and cecal tonsils. Target cells labeled for ATH were immunophenotyped by double labeling. They were positive for CD3, CD8 and the lymphocyte receptor TCR-1, a phenotype characteristic of cytotoxic γδ T cells. Some of the target cells in the spleen were TCR-3 positive. Targeting of lymphocytes by CPV3 indicated that it may also be an immunomodulating hormone.
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The use of transgenic mouse models to reveal the functions of Ca2+ buffer proteins in excitable cells. Biochim Biophys Acta Gen Subj 2012; 1820:1294-303. [DOI: 10.1016/j.bbagen.2011.11.008] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Revised: 11/14/2011] [Accepted: 11/15/2011] [Indexed: 12/19/2022]
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Alpár A, Attems J, Mulder J, Hökfelt T, Harkany T. The renaissance of Ca2+-binding proteins in the nervous system: secretagogin takes center stage. Cell Signal 2012; 24:378-387. [PMID: 21982882 PMCID: PMC3237847 DOI: 10.1016/j.cellsig.2011.09.028] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Accepted: 09/24/2011] [Indexed: 02/03/2023]
Abstract
Effective control of the Ca(2+) homeostasis in any living cell is paramount to coordinate some of the most essential physiological processes, including cell division, morphological differentiation, and intercellular communication. Therefore, effective homeostatic mechanisms have evolved to maintain the intracellular Ca(2+) concentration at physiologically adequate levels, as well as to regulate the spatial and temporal dynamics of Ca(2+)signaling at subcellular resolution. Members of the superfamily of EF-hand Ca(2+)-binding proteins are effective to either attenuate intracellular Ca(2+) transients as stochiometric buffers or function as Ca(2+) sensors whose conformational change upon Ca(2+) binding triggers protein-protein interactions, leading to cell state-specific intracellular signaling events. In the central nervous system, some EF-hand Ca(2+)-binding proteins are restricted to specific subtypes of neurons or glia, with their expression under developmental and/or metabolic control. Therefore, Ca(2+)-binding proteins are widely used as molecular markers of cell identity whilst also predicting excitability and neurotransmitter release profiles in response to electrical stimuli. Secretagogin is a novel member of the group of EF-hand Ca(2+)-binding proteins whose expression precedes that of many other Ca(2+)-binding proteins in postmitotic, migratory neurons in the embryonic nervous system. Secretagogin expression persists during neurogenesis in the adult brain, yet becomes confined to regionalized subsets of differentiated neurons in the adult central and peripheral nervous and neuroendocrine systems. Secretagogin may be implicated in the control of neuronal turnover and differentiation, particularly since it is re-expressed in neoplastic brain and endocrine tumors and modulates cell proliferation in vitro. Alternatively, and since secretagogin can bind to SNARE proteins, it might function as a Ca(2+) sensor/coincidence detector modulating vesicular exocytosis of neurotransmitters, neuropeptides or hormones. Thus, secretagogin emerges as a functionally multifaceted Ca(2+)-binding protein whose molecular characterization can unravel a new and fundamental dimension of Ca(2+)signaling under physiological and disease conditions in the nervous system and beyond.
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Affiliation(s)
- Alán Alpár
- European Neuroscience Institute at Aberdeen, University of Aberdeen, Aberdeen AB25 2ZD, United Kingdom; Division of Molecular Neurobiology, Department of Medical Biochemistry & Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden
| | - Johannes Attems
- Institute for Ageing and Health, Campus for Ageing and Vitality, Newcastle University, Newcastle upon Tyne NE4 5PL, United Kingdom
| | - Jan Mulder
- Science for Life Laboratory, Department of Neuroscience, Karolinska Institutet, Tomtebodavägen 23A, S-17165 Solna, Sweden
| | - Tomas Hökfelt
- Department of Neuroscience, Retzius väg 8, Karolinska Institutet, S-17177 Stockholm, Sweden
| | - Tibor Harkany
- European Neuroscience Institute at Aberdeen, University of Aberdeen, Aberdeen AB25 2ZD, United Kingdom; Division of Molecular Neurobiology, Department of Medical Biochemistry & Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden.
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Zhang J, Shettigar V, Zhang GC, Kindell DG, Liu X, López JJ, Yerrimuni V, Davis GA, Davis JP. Engineering Parvalbumin for the Heart: Optimizing the Mg Binding Properties of Rat β-Parvalbumin. Front Physiol 2011; 2:77. [PMID: 22059076 PMCID: PMC3204457 DOI: 10.3389/fphys.2011.00077] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2011] [Accepted: 10/10/2011] [Indexed: 01/01/2023] Open
Abstract
Parvalbumin (PV), an EF-hand protein family member, is a delayed calcium buffer that exchanges magnesium for calcium to facilitate fast skeletal muscle relaxation. Genetic approaches that express parvalbumin in the heart also enhance relaxation and show promise of being therapeutic against various cardiac diseases where relaxation is compromised. Unfortunately, skeletal muscle PVs have very slow rates of Ca2+ dissociation and are prone to becoming saturated with Ca2+, eventually losing their buffering capability within the constantly beating heart. In order for PV to have a more therapeutic potential in the heart, a PV with faster rates of calcium dissociation and high Mg2+ affinity is needed. We demonstrate that at 35°C, rat β-PV has an ~30-fold faster rate of Ca2+ dissociation compared to rat skeletal muscle α-PV, and still possesses a physiologically relevant Ca2+ affinity (~100 nM). However, rat β-PV will not be a delayed Ca2+ buffer since its Mg2+ affinity is too low (~1 mM). We have engineered two mutations into rat β-PV, S55D and E62D, when observed alone increase Mg2+ affinity up to fivefold, but when combined increase Mg2+ affinity ~13-fold, well within a physiologically relevant affinity. Furthermore, the Mg2+ dissociation rate (172/s) from the engineered S55D, E62D PV is slow enough for delayed Ca2+ buffering. Additionally, the engineered PV retains a high Ca2+ affinity (132 nM) and fast rate of Ca2+ dissociation (64/s). These PV design strategies hold promise for the development of new therapies to remediate relaxation abnormalities in different heart diseases and heart failure.
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Affiliation(s)
- Jianchao Zhang
- Department of Physiology and Cell Biology, The Ohio State University Columbus, OH, USA
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Simmons DD, Tong B, Schrader AD, Hornak AJ. Oncomodulin identifies different hair cell types in the mammalian inner ear. J Comp Neurol 2010; 518:3785-802. [PMID: 20653034 DOI: 10.1002/cne.22424] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The tight regulation of Ca(2+) is essential for inner ear function, and yet the role of Ca(2+) binding proteins (CaBPs) remains elusive. By using immunofluorescence and reverse transcriptase-polymerase chain reaction (RT-PCR), we investigated the expression of oncomodulin (Ocm), a member of the parvalbumin family, relative to other EF-hand CaBPs in cochlear and vestibular organs in the mouse. In the mouse cochlea, Ocm is found only in outer hair cells and is localized preferentially to the basolateral outer hair cell membrane and to the base of the hair bundle. Developmentally, Ocm immunoreactivity begins as early as postnatal day (P) 2 and shows preferential localization to the basolateral membrane and hair bundle after P8. Unlike the cochlea, Ocm expression is substantially reduced in vestibular tissues at older adult ages. In vestibular organs, Ocm is found in type I striolar or central hair cells, and has a more diffuse subcellular localization throughout the hair cell body. Additionally, Ocm immunoreactivity in vestibular hair cells is present as early as E18 and is not obviously affected by mutations that cause a disruption of hair bundle polarity. We also find Ocm expression in striolar hair cells across mammalian species. These data suggest that Ocm may have distinct functional roles in cochlear and vestibular hair cells.
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Affiliation(s)
- Dwayne D Simmons
- Department of Integrative Biology and Physiology and the Brain Research Institute, University of California Los Angeles, Los Angeles, California 90095, USA.
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Abstract
"Ca(2+) buffers," a class of cytosolic Ca(2+)-binding proteins, act as modulators of short-lived intracellular Ca(2+) signals; they affect both the temporal and spatial aspects of these transient increases in [Ca(2+)](i). Examples of Ca(2+) buffers include parvalbumins (α and β isoforms), calbindin-D9k, calbindin-D28k, and calretinin. Besides their proven Ca(2+) buffer function, some might additionally have Ca(2+) sensor functions. Ca(2+) buffers have to be viewed as one of the components implicated in the precise regulation of Ca(2+) signaling and Ca(2+) homeostasis. Each cell is equipped with proteins, including Ca(2+) channels, transporters, and pumps that, together with the Ca(2+) buffers, shape the intracellular Ca(2+) signals. All of these molecules are not only functionally coupled, but their expression is likely to be regulated in a Ca(2+)-dependent manner to maintain normal Ca(2+) signaling, even in the absence or malfunctioning of one of the components.
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