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Data on the structure of G-quadruplexes, noncanonical nucleic acid forms, supporting an idea of their potential participation in regulation of gene expression in response to the change in intracellular Na+i/K+i ratio are considered in the review. Structural variety of G-quadruplexes, role of monovalent cations in formation of this structure, and thermodynamic stability of G-quadruplexes are described. Data on the methods of their identification in the cells and biological functions of these structures are presented. Analysis of information about specific interactions of G-quadruplexes with some proteins was conducted, and their potential participation in the development of some pathological conditions, in particular, cancer and neurodegenerative diseases, is considered. Special attention is given to the plausible role of G-quadruplexes as sensors of intracellular Na+i/K+i ratio, because alteration of this parameter affects folding of G-quadruplexes changing their stability and, thereby, organization of the regulatory elements of nucleic acids. The data presented in the conclusion section demonstrate significant change in the expression of some early response genes under certain physiological conditions of cells and tissues depending on the intracellular Na+i/K+i ratio. [ABSTRACT FROM AUTHOR]

In rat vascular smooth muscle cells (RVSMC), 3-h Na + ,K + -ATPase inhibition by ouabain or in K + -free medium resulted in the inversion of the [Na + ] i /[K + ] i ratio and elevation up to 7-fold the content of Egr1, Atf3, Nr4a1 and Ptgs2 mRNAs. Ouabain increased the rate of 45Ca 2+ influx by 2-fold that was abolished by L-type voltage-gated Ca 2+ channel blocker nicardipine, but it was resistant to Na + /Ca 2+ exchanger inhibitor KB-R7943. To study the role of Ca 2+ -mediated signaling in the expression of Na + i /K + i -sensitive genes we used intracellular Ca 2+ chelator BAPTA and incubated RVSMC in Ca 2+ -free medium. The elevation of Nr4a1 and Ptgs2 expression triggered by ouabain was diminished in Ca 2+ -depeleted cells as well as in the presence of nicardipine and calmodulin antagonists A-7 and W-7. Ptgs2 expression was also suppressed by inhibitor of Ca 2+ /calmodulin-dependent protein kinase (CaMKII) KN-93 whereas increment of Nr4a1 content triggered by ouabain was attenuated by inhibitor of Ca 2+ /calmodulin-dependent protein phosphatase (calcineurin, CaN) cyclosporin A. Neither Ca 2+ depletion nor above listed compounds had any impact on the augmented expression of Egr1 and Atf3 in ouabain-treated RVSMC. Our results strongly suggest that dissipation of transmembrane gradient of monovalent cations increases Ptgs2 and Nr4a1 transcription via augment Ca 2+ influx through L-type Ca 2+ channels that, in turn, leads to CaMKII-mediated phosphorylation of CREB and calcineurin-mediated dephosphorylation of NFAT, respectively. Additional experiments should be performed to identify intermediates of Na + i ,K + i -mediated Ca 2+ -independent excitation-transcription coupling involved the regulation of Egr1 and Atf3 expression. [ABSTRACT FROM AUTHOR]

Stimulus-dependent elevation of intracellular Ca2+ affects gene expression via well-documented calmodulin-mediated signaling pathways. Recently, we found that the addition of extra- and intracellular Ca2+ chelators increased, rather than decreased, the number of genes expressed, and that this is affected by the elevation of [Na+]i/[K+]i-ratio. This assumes the existence of a novel Na+i/K+i-mediated Ca2+i-independent mechanism of excitation-transcription coupling. To identify upstream Na+i/K+i-sensitive genes, we examined the kinetics of transcriptomic changes in human umbilical vein endothelial cells (HUVEC) subjected to Na,K-ATPase inhibition by ouabain or K+-free medium. According to our data, microRNAs, transcription factors, and proteins involved in immune response and inflammation might be considered as key components of Na+i/K+i-mediated excitation-transcription coupling. Special attention was focused on the FOS gene and the possible mechanism of transcription regulation via G-quadruplexes, non-canonical secondary structures of nucleic acids, whose stability depends on [Na+]i/[K+]i-ratio. Verification of the [Na+]i/[K+]i-sensitive transcription regulation mechanism should be continued in forthcoming studies. [ABSTRACT FROM AUTHOR]

Recent studies demonstrated that in addition to Na+,K+-ATPase inhibition cardiotonic steroids (CTSs) affect diverse intracellular signaling pathways. This study examines the relative impact of [Na+]i/[K+]i-mediated and -independent signaling in transcriptomic changes triggered by the endogenous CTSs ouabain and marinobufagenin (MBG) in human umbilical vein endothelial cells (HUVEC). We noted that prolongation of incubation increased the apparent affinity for ouabain estimated by the loss of [K+]i and gain of [Na+]i. Six hour exposure of HUVEC to 100 and 3,000 nM ouabain resulted in elevation of the [Na+]i/[K+]i ratio by ~15 and 80-fold and differential expression of 258 and 2185 transcripts, respectively. Neither [Na+]i/[K+]i ratio nor transcriptome were affected by 6-h incubation with 30 nM ouabain. The 96-h incubation with 3 nM ouabain or 30 nM MBG elevated the [Na+]i/[K+]i ratio by ~14 and 3-fold and led to differential expression of 880 and 484 transcripts, respectively. These parameters were not changed after 96-h incubation with 1 nM ouabain or 10 nM MBG. Thus, our results demonstrate that elevation of the [Na+]i/[K+]i ratio is an obligatory step for transcriptomic changes evoked by CTS in HUVEC. The molecular origin of upstream [Na+]i/[K+]i sensors involved in transcription regulation should be identified in forthcoming studies. [ABSTRACT FROM AUTHOR]

With an exception of few reports, the plasma concentration of ouabain and marinobufagenin, mostly studied cardiotonic steroids (CTS) assessed by immunoassay techniques, is less than 1 nM. During the last 3 decades, the implication of these endogenous CTS in the pathogenesis of hypertension and other volume-expanded disorders is widely disputed. The threshold for inhibition by CTS of human and rodent α1-Na,K-ATPase is ∼1 and 1000 nM, respectively, that rules out the functioning of endogenous CTS (ECTS) as natriuretic hormones and regulators of cell adhesion, cell-to-cell communication, gene transcription and translation, which are mediated by dissipation of the transmembrane gradients of monovalent cations. In several types of cells ouabain and marinobufagenin at concentrations corresponding to its plasma level activate Na,K-ATPase, decrease the [Na + ] i /[K + ] i -ratio and increase cell proliferation. Possible physiological significance and mechanism of non-canonical Na + i /K + i -dependent and Na + i /K + i -independent cell responses to CTS are discussed., (© 2020 Chongqing Medical University. Production and hosting by Elsevier B.V.)

Background/aims: Prolonged hyperosmotic shrinkage evokes expression of osmoprotective genes via nuclear factor NFAT5-mediated pathway and activates Na + influx via hypertonicity-induced cation channels (HICC). In human umbilical vein endothelial cells (HUVEC) elevation of intracellular sodium concentration ([Na + ] i ) triggers transcription of dozens of early response genes (ERG). This study examined the role of monovalent cations in the expression of Na + i -sensitive ERGs in iso- and hyperosmotically shrunken HUVEC., Methods: Cell volume was measured by 3D reconstruction of cell shape and as 14 C-urea available space. Intracellular Na + and K + content was measured by flame atomic absorption spectrometry. ERG transcription was estimated by RT-PCR., Results: Elevation of medium osmolality by 150 mM mannitol or cell transfer from hypo- to isosmotic medium decreased cell volume by 40-50%. Hyperosmotic medium increased [Na + ] i by 2-fold whereas isosmotic shrinkage had no impact on this parameter. Hyperosmotic but not isosmotic shrinkage increased up-to 5-fold the content of EGR1, FOS, ATF3, ZFP36 and JUN mRNAs. Expression of these ERGs triggered by hyperosmotic shrinkage and Na + ,K + -ATPase inhibition by 0.1 µM ouabain exhibited positive correlation (R 2 =0.9383, p=0.0005). Isosmotic substitution of NaCl by N-methyl-D-glucamine abolished an increment of [Na + ] i and ERG expression triggered by mannitol addition., Conclusion: Augmented expression of ERGs in hyperosmotically shrunken HUVEC is mediated by elevation of [Na + ] i ., Competing Interests: The authors declare no competing financial interests., (© Copyright by the Author(s). Published by Cell Physiol Biochem Press.)

In rat vascular smooth muscle cells (RVSMC), 3-h Na + ,K + -ATPase inhibition by ouabain or in K + -free medium resulted in the inversion of the [Na + ] i /[K + ] i ratio and elevation up to 7-fold the content of Egr1, Atf3, Nr4a1 and Ptgs2 mRNAs. Ouabain increased the rate of 45Ca 2+ influx by 2-fold that was abolished by L-type voltage-gated Ca 2+ channel blocker nicardipine, but it was resistant to Na + /Ca 2+ exchanger inhibitor KB-R7943. To study the role of Ca 2+ -mediated signaling in the expression of Na + i /K + i -sensitive genes we used intracellular Ca 2+ chelator BAPTA and incubated RVSMC in Ca 2+ -free medium. The elevation of Nr4a1 and Ptgs2 expression triggered by ouabain was diminished in Ca 2+ -depeleted cells as well as in the presence of nicardipine and calmodulin antagonists A-7 and W-7. Ptgs2 expression was also suppressed by inhibitor of Ca 2+ /calmodulin-dependent protein kinase (CaMKII) KN-93 whereas increment of Nr4a1 content triggered by ouabain was attenuated by inhibitor of Ca 2+ /calmodulin-dependent protein phosphatase (calcineurin, CaN) cyclosporin A. Neither Ca 2+ depletion nor above listed compounds had any impact on the augmented expression of Egr1 and Atf3 in ouabain-treated RVSMC. Our results strongly suggest that dissipation of transmembrane gradient of monovalent cations increases Ptgs2 and Nr4a1 transcription via augment Ca 2+ influx through L-type Ca 2+ channels that, in turn, leads to CaMKII-mediated phosphorylation of CREB and calcineurin-mediated dephosphorylation of NFAT, respectively. Additional experiments should be performed to identify intermediates of Na + i ,K + i -mediated Ca 2+ -independent excitation-transcription coupling involved the regulation of Egr1 and Atf3 expression., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Recent studies demonstrated that in addition to Na + ,K + -ATPase inhibition cardiotonic steroids (CTSs) affect diverse intracellular signaling pathways. This study examines the relative impact of [Na + ] i /[K + ] i -mediated and -independent signaling in transcriptomic changes triggered by the endogenous CTSs ouabain and marinobufagenin (MBG) in human umbilical vein endothelial cells (HUVEC). We noted that prolongation of incubation increased the apparent affinity for ouabain estimated by the loss of [K + ] i and gain of [Na + ] i . Six hour exposure of HUVEC to 100 and 3,000 nM ouabain resulted in elevation of the [Na + ] i /[K + ] i ratio by ~15 and 80-fold and differential expression of 258 and 2185 transcripts, respectively. Neither [Na + ] i /[K + ] i ratio nor transcriptome were affected by 6-h incubation with 30 nM ouabain. The 96-h incubation with 3 nM ouabain or 30 nM MBG elevated the [Na + ] i /[K + ] i ratio by ~14 and 3-fold and led to differential expression of 880 and 484 transcripts, respectively. These parameters were not changed after 96-h incubation with 1 nM ouabain or 10 nM MBG. Thus, our results demonstrate that elevation of the [Na + ] i /[K + ] i ratio is an obligatory step for transcriptomic changes evoked by CTS in HUVEC. The molecular origin of upstream [Na + ] i /[K + ] i sensors involved in transcription regulation should be identified in forthcoming studies.