Abstract
Since being first described more than 60 years ago, Na,K-ATPase has been extensively studied, while novel concepts about its structure, physiology, and biological roles continue to be elucidated. Cardiac glycosides not only inhibit the pump function of Na,K-ATPase but also activate intracellular signal transduction pathways, which are important in many biological processes. Recently, antiviral effects have been described as a novel feature of Na,K-ATPase inhibition with the use of cardiac glycosides. Cardiac glycosides have been reported to be effective against both DNA viruses such as cytomegalovirus and herpes simplex and RNA viruses such as influenza, chikungunya, coronavirus, and respiratory syncytial virus, among others. Consequently, cardiac glycosides have emerged as potential broad-spectrum antiviral drugs, with the great advantage of targeting cell host proteins, which help to minimize resistance to antiviral treatments, making them a very promising strategy against human viral infections. Here, we review the effect of cardiac glycosides on viral biology and the mechanisms by which these drugs impair the replication of this array of different viruses.
1. Introduction
Since first described by Skou more than 60 years ago [1], Na,K-ATPase has been extensively studied, and novel concepts about structure, physiology, and biological roles continue to appear. The classical role of Na,K-ATPase is to maintain the electrolyte homeostasis of the cells by pumping cations in and out of the cell using the energy obtained from the hydrolysis of (Adenosine triphosphate) ATP. However, Na,K-ATPase is also a key scaffolding protein that is able to interact with signaling proteins such as protein kinase C (PKC) and phosphoinositide 3-kinase (PI3K) [2,3,4,5]. It also works as a classical receptor in which the binding of cardiac glycosides induces activation of the tyrosine kinase Src and down-stream signaling cascades, independent of changes in intracellular ions [6,7,8]. Viruses are intracellular parasites whose life cycle is dependent on hijacking cellular functions like protein synthesis and intracellular transport of molecules to promote their replication and spreading. The infection begins with the attachment of the viral particle to surface-exposed cellular molecules and their entry to the cell by endocytosis. Once the viral components are in the intracellular environment and the genome is transcribed, the viral proteins are synthesized using the host cell translational machinery, and the new viral particles are transported to the surface to be released and infect other cells [9]. Viruses are very frequent causative agents of human infectious diseases and cancer, and their treatment is often challenging, as resistance to antiviral drugs has been reported for many important pathogens such as influenza, hepatitis B, and herpes simplex virus [10,11,12,13]. Targeting host cell components such as Na,K-ATPase is a very promising antiviral strategy in order to minimize the resistance to antiviral drugs, and has been shown to be effective in a broad spectrum of viral species. In this review, we analyze both the effects that viral infection have on the Na,K-ATPase function and the effect of Na,K-ATPase ligands cardiac glycosides on viral biology. We will also review the mechanisms by which these drugs impair the replication of different types of viruses (Table 1).
Table 1.
Summary of cardiac glicosides with reported antiviral activity.
2. Na,K-ATPase Function Altered by Viral Infection
Na,K-ATPase function can be directly affected by both DNA and RNA viruses. Human parvovirus B19 is a DNA virus with tropism for erythroid progenitor cells causing erythema infectiosum (fifth disease) in children and other pathologic conditions such as arthropathies and pure red blood cell aplasia [29]. The expression of human parvovirus B19 capsid protein VP1 decreases Na,K-ATPase activity in Xenopus oocytes partially due to the VP1 phospholipase A2 activity dependent formation of lysophosphatidylcholine [30]. In addition, Chiu et al. found that recombinant VP1 can also decrease Na,K-ATPase expression in A549 cells [31]. Infection by RNA viruses can also affect the expression and activity of the Na,K-ATPase. Na,K-ATPase is downregulated in alveolar epithelial cells infected with influenza A H1N1 and H5N1strains, affecting alveolar fluid clearance [32]. In addition, influenza A virus infection induces decreased expression of Na,K-ATPase in the plasma membrane of alveolar epithelial cells with paracrine factors released from infected cells [33]. Na,K-ATPase activity can also be decreased by sindbis virus [34] and enterovirus coxsackie B infection [35], causing important changes in the intracellular concentration of potassium and sodium and consequently in membrane potential [36]. Interestingly, enterovirus 71 (EV71), agent of hand- foot-and-mouth disease (HFMD) in pediatric population, interacts with the β3 subunit of the Na,K-ATPase causing an increase of its expression [37].
3. DNA Viruses Affected by Na,K-ATPase Modulation
Cardiac glycosides are a family of steroidal compounds commonly used in the treatment of cardiac diseases. These glycosides inhibit the Na,K-ATPase pump function, resulting in changes in the intracellular concentrations of sodium, potassium, and calcium [38], and also trigger signaling transduction pathways at low concentrations [14]. It is not well understood whether the action of cardiac glycosides on viral replication is due to changes in ion homeostasis, or by activation of intracellular signaling pathways; however, these compounds are effective on a diversity of viruses, from which we infer that there are mechanisms affecting host processes that are crucial for viral replication. Cardiac glycosides inhibit cytomegalovirus (CMV) replication, a herpesvirus causative of important human diseases, at nanomolar concentrations [15], with an additive effect when combined with antiviral drugs for CMV as ganciclovir [16]. In a recent publication by Cohen et al., a panel of cardiac glycosides was used to study its efficacy against CMV in human lung fibroblasts, and it was found that the inhibitory activity on CMV replication was due to a decrease in viral protein translation, and that the antiviral potency depended on the structure of the cardiac glycosides and its specific interaction with the Na,K-ATPase [17]. Cardiac glycosides can also be effective on other DNA viruses such as herpes simplex virus (HSV) by inhibiting the expression of viral genes, with the antiviral action correlated with the potency against the Na,K-ATPase [18]. In addition, Su et al. have reported that digitoxin inhibits HSV replication with a 50% effective concentration (EC50) of 0.05 µM, while the EC50 for classical anti HSV drugs (acyclovir and ganciclovir) is higher than 1.5 µM. Digitoxin impaired the HSV viral life cycle at two different steps: viral DNA synthesis and viral release form the host cells. The authors also showed that others cardiac glycosides such as digoxin, ouabain, and G-strophanthin have comparable anti-HSV activity [19]. Finally, adenoviruses, which are common human pathogens, are also susceptible to cardiac glycosides such as digitoxin and digoxin, which are able to impair adenovirus genome replication by altering the host pre-RNA splicing machinery [39].
4. RNA Viruses Affected by Na,K-ATPase Modulation
A diversity of RNA viruses is vulnerable to cardiac glycosides treatment. Chikungunya virus, the agent of a human epidemic mosquito-borne disease [20], is susceptible to treatment with cardiac glycosides. Ashbrook et al. screened a library of small molecules for the capacity to modulate chikungunya virus infection in human osteosarcoma cells and found that digoxin has antiviral activity on chikungunya and other alphaviruses (including river virus, sindbis virus, and vesicular stomatitis virus) by impairing the viral cycle at post entry steps via inhibition of Na,K-ATPase [40]. Moreover, other RNA viruses are affected by Na,K-ATPase inhibition. Coronaviruses, which cause intestinal and respiratory diseases and are responsible for middle-east respiratory syndrome (MERS-CoV) and epidemic severe acute respiratory syndrome (SARS-CoV) in humans [21], are repressed when the Na,K-ATPase α1-subunit is silenced or inhibited by low dose of cardiac glycosides, an effect caused by an impairment of the virus entry at an early stage. Importantly, the cardiac glycosides’ antiviral effect is relieved by inhibition of the Src pathway [22]. Transmissible gastroenteritis coronavirus (TGEV) is also susceptible to ouabain and digitoxin [41]. The respiratory syncytial virus (RSV) is a common cause of seasonal respiratory disease in children, which can lead to severe respiratory failure, contributing to hospitalization and mortality in the pediatric population [23]; no specific antiviral treatment or vaccine is yet available. Ouabain at a concentration of 10 nM inhibits RSV replication in an in vitro model [42]. Also, ebola virus (EV), which triggers severe hemorrhagic fever in humans with a high mortality rate, can be inhibited by cardiac glycosides. Na,K-ATPase was identified in a proteomic analysis of EV interaction with host cell proteins, and nanomolar concentrations of ouabain were able to impair the viral replication by decreasing the levels of viral RNA [24]. Additionally, this finding was confirmed by a screening of compounds with activity against EV [25]. Influenza is an infectious disease caused by various types of influenza virus, and it is characterized by a highly contagious, acute respiratory syndrome that carries significant morbidity and mortality worldwide. Many influenza strains have developed pharmacological resistance to available antiviral drugs, and the development of new anti-influenza treatments has been of great interest in recent years. Pharmacological screening studies have highlighted the potential efficacy of cardiac glycosides as anti-influenza drugs. A high-throughput screen made by Hoffmann et al. found that nanomolar doses of Na,K-ATPase inhibitors, such as ouabain and lanatoside C, exert inhibition on influenza virus replication in vitro [43]. Moreover, the β1 subunit of the Na,K-ATPase interacts with the M2 and BM2 influenza A proteins and their knockdown decreases influenza virus replication [26]. We have also observed that the inhibition of Na,K-ATPase by cardiac glycosides decreases influenza virus replication by inhibiting the host cell translational machinery via a decrease in intracellular potassium [44]. Consistently with this, other authors have shown that ouabain does not affect the budding rate of the influenza virus in MDCK (Madin-Darby Canine Kidney) infected cells [45]. Interestingly, human immunodeficiency virus (HIV) can also be susceptible to cardiac glycosides treatment. HIV infection is a worldwide spread infectious disease affecting more than 30 million people around the globe that can lead to acquired immunodeficiency syndrome or AIDS if not treated, increasing the risk for opportunistic infections and some types of cancer [46]. In a screening study by Laird et al., different members of the cardiac glycosides family were shown to be active against HIV-1 [27]; moreover, Wong et al. demonstrated that digoxin inhibits the replication of clinical strains of HIV-1 by impairing the splicing mechanism of viral RNA and consequently diminishing the structural protein synthesis of the virus [28]. Recent work published by the same group reported that low concentrations of cardiac glycosides inhibit HIV-1 gene expression through modulation of the mitogen-activated protein kinases/extracellular signal-regulated kinases (MEK1/2-ERK1/2) signaling via interaction with the Na,K-ATPase, independent of alterations in intracellular calcium [47].
6. Conclusions
Na,K-ATPase is a ubiquitous transmembrane protein that not only pumps ions in and out of the cell but also plays an important role in intracellular signaling processes. Due to its effect on Na,K-ATPase, the use of cardiac glycosides as antiviral drugs is very promising. The strong inhibitory effects of these drugs occur at different levels of the life cycle of different virus species. However, in the publications that profoundly studied the mechanism of action of cardiac glycosides as antiviral drugs, the main findings correlate with either an impairment on the viral genome replication or a decrease in the viral mRNA or protein synthesis, suggesting that this drugs target host processes that are essential for the viruses to accomplish a successful replication cycle. These mechanisms should be further explored in order to develop novel antiviral treatments with two very important advantages: low risk of resistance and broad spectrum of action.
Funding
This research was funded by the National Institute of Health, grant number HL-071643 y HL-048129.
Acknowledgments
We thank Jacob I. Sznajder for support and insightful discussions.
Conflicts of Interest
The authors declare no conflict of interest.
References
- Skou, J.C. The influence of some cations on an adenosine triphosphatase from peripheral nerves. Biochim. Biophys. Acta 1957, 23, 394–401. [Google Scholar] [CrossRef]
- Huang, L.; Xie, Z.; Huang, W.H.; Askari, A. Partial inhibition of Na+/K+-ATPase by ouabain induces the Ca2+-dependent expressions of early-response genes in cardiac myocytes. J. Biol. Chem. 1996, 271, 10372–10378. [Google Scholar]
- Huang, L.; Li, H.; Xie, Z. Ouabain-induced hypertrophy in cultured cardiac myocytes is accompanied by changes in expression of several late response genes. J. Mol. Cell. Cardiol. 1997, 29, 429–437. [Google Scholar] [CrossRef] [PubMed]
- Huang, L.; Kometiani, P.; Xie, Z. Differential regulation of Na/K-ATPaseα-subunit isoform gene expressions in cardiac myocytes by ouabain and other hypertrophic stimuli. J. Mol. Cell. Cardiol. 1997, 29, 3157–3167. [Google Scholar] [CrossRef] [PubMed]
- Mohammadi, K.; Kometiani, P.; Xie, Z.; Askari, A. Role of protein kinase c in the signal pathways that link Na+/K+-atpase to ERK1/2. J. Biol. Chem. 2001, 276, 42050–42056. [Google Scholar] [CrossRef] [PubMed]
- Liu, J.; Tian, J.; Haas, M.; Shapiro, J.I.; Askari, A.; Xie, Z. Ouabain interaction with cardiac Na+/K+-ATPase initiates signal cascades independent of changes in intracellular Na+ and Ca2+ concentrations. J. Biol. Chem. 2000, 275, 27838–27844. [Google Scholar] [PubMed]
- Tian, J.; Cai, T.; Yuan, Z.; Wang, H.; Liu, L.; Haas, M.; Maksimova, E.; Huang, X.-Y.; Xie, Z.J. Binding of Src to Na+/K+-ATPase forms a functional signaling complex. Mol. Biol. Cell 2006, 17, 317–326. [Google Scholar] [CrossRef] [PubMed]
- Haas, M.; Askari, A.; Xie, Z. Involvement of Src and epidermal growth factor receptor in the signal-transducing function of Na+/K+-ATPase. J. Biol. Chem. 2000, 275, 27832–27837. [Google Scholar] [CrossRef] [PubMed]
- Boulant, S.; Stanifer, M.; Lozach, P.Y. Dynamics of virus-receptor interactions in virus binding, signaling, and endocytosis. Viruses 2015, 7, 2794–2815. [Google Scholar] [CrossRef] [PubMed]
- Gubareva, L.V.; Besselaar, T.G.; Daniels, R.S.; Fry, A.; Gregory, V.; Huang, W.; Hurt, A.C.; Jorquera, P.A.; Lackenby, A.; Leang, S.K.; et al. Global update on the susceptibility of human influenza viruses to neuraminidase inhibitors, 2015–2016. Antivir. Res. 2017, 146, 12–20. [Google Scholar] [CrossRef] [PubMed]
- Burrel, S.; Aime, C.; Hermet, L.; Ait-Arkoub, Z.; Agut, H.; Boutolleau, D. Surveillance of herpes simplex virus resistance to antivirals: A 4-year survey. Antivir. Res. 2013, 100, 365–372. [Google Scholar] [CrossRef] [PubMed]
- Zhang, Q.; Liao, Y.; Chen, J.; Cai, B.; Su, Z.; Ying, B.; Lu, X.; Tao, C.; Wang, L. Epidemiology study of hbv genotypes and antiviral drug resistance in multi-ethnic regions from western China. Sci. Rep. 2015, 5, 17413. [Google Scholar] [CrossRef] [PubMed]
- Zur Hausen, H. The search for infectious causes of human cancers: Where and why (nobel lecture). Angew. Chem. Int. Ed. 2009, 48, 5798–5808. [Google Scholar] [CrossRef] [PubMed]
- Xie, Z. Molecular mechanisms of Na/K-ATPase-mediated signal transduction. Ann. N. Y. Acad. Sci. 2003, 986, 497–503. [Google Scholar] [CrossRef] [PubMed]
- Kapoor, A.; Cai, H.; Forman, M.; He, R.; Shamay, M.; Arav-Boger, R. Human cytomegalovirus inhibition by cardiac glycosides: Evidence for involvement of the herg gene. Antimicrob. Agents Chemother. 2012, 56, 4891–4899. [Google Scholar] [CrossRef] [PubMed]
- Cai, H.; Kapoor, A.; He, R.; Venkatadri, R.; Forman, M.; Posner, G.H.; Arav-Boger, R. In vitro combination of anti-cytomegalovirus compounds acting through different targets: Role of the slope parameter and insights into mechanisms of action. Antimicrob. Agents Chemother. 2014, 58, 986–994. [Google Scholar] [CrossRef] [PubMed]
- Cohen, T.; Williams, J.D.; Opperman, T.J.; Sanchez, R.; Lurain, N.S.; Tortorella, D. Convallatoxin-induced reduction of methionine import effectively inhibits human cytomegalovirus infection and replication. J. Virol. 2016, 90, 10715–10727. [Google Scholar] [CrossRef] [PubMed]
- Dodson, A.W.; Taylor, T.J.; Knipe, D.M.; Coen, D.M. Inhibitors of the sodium potassium atpase that impair herpes simplex virus replication identified via a chemical screening approach. Virology 2007, 366, 340–348. [Google Scholar] [CrossRef] [PubMed]
- Su, C.T.; Hsu, J.T.; Hsieh, H.P.; Lin, P.H.; Chen, T.C.; Kao, C.L.; Lee, C.N.; Chang, S.Y. Anti-HSV activity of digitoxin and its possible mechanisms. Antivir. Res. 2008, 79, 62–70. [Google Scholar] [CrossRef] [PubMed]
- Ganesan, V.K.; Duan, B.; Reid, S.P. Chikungunya virus: Pathophysiology, mechanism, and modeling. Viruses 2017, 9, 368. [Google Scholar] [CrossRef] [PubMed]
- Bailey, E.S.; Fieldhouse, J.K.; Choi, J.Y.; Gray, G.C. A mini review of the zoonotic threat potential of influenza viruses, coronaviruses, adenoviruses, and enteroviruses. Front. Public Health 2018, 6, 104. [Google Scholar] [CrossRef] [PubMed]
- Burkard, C.; Verheije, M.H.; Haagmans, B.L.; van Kuppeveld, F.J.; Rottier, P.J.; Bosch, B.J.; de Haan, C.A. ATP1A1-mediated Src signaling inhibits coronavirus entry into host cells. J. Virol. 2015, 89, 4434–4448. [Google Scholar] [CrossRef] [PubMed]
- Stein, R.T.; Bont, L.J.; Zar, H.; Polack, F.P.; Park, C.; Claxton, A.; Borok, G.; Butylkova, Y.; Wegzyn, C. Respiratory syncytial virus hospitalization and mortality: Systematic review and meta-analysis. Pediatr. Pulmonol. 2017, 52, 556–569. [Google Scholar] [CrossRef] [PubMed]
- Garcia-Dorival, I.; Wu, W.; Dowall, S.; Armstrong, S.; Touzelet, O.; Wastling, J.; Barr, J.N.; Matthews, D.; Carroll, M.; Hewson, R.; et al. Elucidation of the ebola virus VP24 cellular interactome and disruption of virus biology through targeted inhibition of host-cell protein function. J. Proteome Res. 2014, 13, 5120–5135. [Google Scholar] [CrossRef] [PubMed]
- Dowall, S.D.; Bewley, K.; Watson, R.J.; Vasan, S.S.; Ghosh, C.; Konai, M.M.; Gausdal, G.; Lorens, J.B.; Long, J.; Barclay, W.; et al. Antiviral screening of multiple compounds against ebola virus. Viruses 2016, 8, 277. [Google Scholar] [CrossRef] [PubMed]
- Mi, S.; Li, Y.; Yan, J.; Gao, G.F. Na+/K+-ATPase beta1 subunit interacts with M2 proteins of influenza a and B viruses and affects the virus replication. Sci. China Life Sci. 2010, 53, 1098–1105. [Google Scholar] [CrossRef] [PubMed]
- Laird, G.M.; Eisele, E.E.; Rabi, S.A.; Nikolaeva, D.; Siliciano, R.F. A novel cell-based high-throughput screen for inhibitors of HIV-1 gene expression and budding identifies the cardiac glycosides. J. Antimicrob. Chemother. 2014, 69, 988–994. [Google Scholar] [CrossRef] [PubMed]
- Wong, R.W.; Balachandran, A.; Ostrowski, M.A.; Cochrane, A. Digoxin suppresses HIV-1 replication by altering viral RNA processing. PLoS Pathog. 2013, 9, e1003241. [Google Scholar] [CrossRef] [PubMed]
- Bonvicini, F.; Bua, G.; Gallinella, G. Parvovirus b19 infection in pregnancy-awareness and opportunities. Curr. Opin. Virol. 2017, 27, 8–14. [Google Scholar] [CrossRef] [PubMed]
- Almilaji, A.; Szteyn, K.; Fein, E.; Pakladok, T.; Munoz, C.; Elvira, B.; Towhid, S.T.; Alesutan, I.; Shumilina, E.; Bock, C.T.; et al. Down-regulation of Na+/K+ ATPase activity by human parvovirus b19 capsid protein VP1. Cell Physiol. Biochem. 2013, 31, 638–648. [Google Scholar] [CrossRef] [PubMed]
- Chiu, C.C.; Shi, Y.F.; Yang, J.J.; Hsiao, Y.C.; Tzang, B.S.; Hsu, T.C. Effects of human parvovirus b19 and bocavirus VP1 unique region on tight junction of human airway epithelial a549 cells. PLoS ONE 2014, 9, e107970. [Google Scholar] [CrossRef] [PubMed]
- Chan, M.C.; Kuok, D.I.; Leung, C.Y.; Hui, K.P.; Valkenburg, S.A.; Lau, E.H.; Nicholls, J.M.; Fang, X.; Guan, Y.; Lee, J.W.; et al. Human mesenchymal stromal cells reduce influenza A H5N1-associated acute lung injury in vitro and in vivo. Proc. Natl. Acad. Sci. USA 2016, 113, 3621–3626. [Google Scholar] [CrossRef] [PubMed]
- Peteranderl, C.; Morales-Nebreda, L.; Selvakumar, B.; Lecuona, E.; Vadasz, I.; Morty, R.E.; Schmoldt, C.; Bespalowa, J.; Wolff, T.; Pleschka, S.; et al. Macrophage-epithelial paracrine crosstalk inhibits lung edema clearance during influenza infection. J. Clin. Investig. 2016, 126, 1566–1580. [Google Scholar] [CrossRef] [PubMed]
- Ulug, E.T.; Garry, R.F.; Bose, H.R., Jr. Inhibition of Na+K+ATPase activity in membranes of sindbis virus-infected chick cells. Virology 1996, 216, 299–308. [Google Scholar] [CrossRef] [PubMed]
- Nikonov, O.S.; Chernykh, E.S.; Garber, M.B.; Nikonova, E.Y. Enteroviruses: Classification, diseases they cause, and approaches to development of antiviral drugs. Biochemistry 2017, 82, 1615–1631. [Google Scholar] [CrossRef] [PubMed]
- Modalsli, K.; Bukholm, G.; Mikalsen, S.O.; Degre, M. Coxsackie b1 virus-induced changes in cell membrane-associated functions are not responsible for altered sensitivity to bacterial invasiveness. Arch. Virol. 1992, 124, 321–332. [Google Scholar] [CrossRef] [PubMed]
- Lu, Y.; Hou, H.; Wang, F.; Qiao, L.; Wang, X.; Yu, J.; Liu, W.; Sun, Z. Atp1b3: A virus-induced host factor against EV71 replication by up-regulating the production of type-I interferons. Virology 2016, 496, 28–34. [Google Scholar] [CrossRef] [PubMed]
- Prassas, I.; Diamandis, E.P. Novel therapeutic applications of cardiac glycosides. Nat. Rev. Drug Discov. 2008, 7, 926–935. [Google Scholar] [CrossRef] [PubMed]
- Grosso, F.; Stoilov, P.; Lingwood, C.; Brown, M.; Cochrane, A. Suppression of adenovirus replication by cardiotonic steroids. J. Virol. 2017, 91, e01623-16. [Google Scholar] [CrossRef] [PubMed]
- Ashbrook, A.W.; Lentscher, A.J.; Zamora, P.F.; Silva, L.A.; May, N.A.; Bauer, J.A.; Morrison, T.E.; Dermody, T.S. Antagonism of the sodium-potassium atpase impairs chikungunya virus infection. MBio 2016, 7, e00693-16. [Google Scholar] [CrossRef] [PubMed]
- Yang, C.W.; Chang, H.Y.; Hsu, H.Y.; Lee, Y.Z.; Chang, H.S.; Chen, I.S.; Lee, S.J. Identification of anti-viral activity of the cardenolides, Na+/K+-ATPase inhibitors, against porcine transmissible gastroenteritis virus. Toxicol. Appl. Pharmacol. 2017, 332, 129–137. [Google Scholar] [CrossRef] [PubMed]
- Cui, R.; Wang, Y.; Wang, L.; Li, G.; Lan, K.; Altmeyer, R.; Zou, G. Cyclopiazonic acid, an inhibitor of calcium-dependent atpases with antiviral activity against human respiratory syncytial virus. Antivir. Res. 2016, 132, 38–45. [Google Scholar] [CrossRef] [PubMed]
- Hoffmann, H.; Palese, P.; Shaw, M. Modulation of influenza virus replication by alteration of sodium ion transport and protein kinase c activity. Antivir. Res. 2008, 80, 124–134. [Google Scholar] [CrossRef] [PubMed]
- Amarelle, L.K.J.; Lecuona, E.; Shigemura, M.; Welch, L.C.; Peteranderl, C.; Herold, S.V.; Sznajder, J.I. Na,K-ATPase inhibition inhibits influenza a viral replication. In Proceedings of the American Thoracic Society 2017 International Conference, Washington, DC, USA, 19–24 May 2017; p. A2793. [Google Scholar]
- Hui, E.K.; Nayak, D.P. Role of atp in influenza virus budding. Virology 2001, 290, 329–341. [Google Scholar] [CrossRef] [PubMed]
- Unaids. World Aids Day 2017 Fact Sheet. Available online: http://www.unaids.org/sites/default/files/media_asset/UNAIDS_FactSheet_en.pdf (accessed on 12 June 2018).
- Wong, R.W.; Lingwood, C.A.; Ostrowski, M.A.; Cabral, T.; Cochrane, A. Cardiac glycoside/aglycones inhibit HIV-1 gene expression by a mechanism requiring MEK1/2-ERK1/2 signaling. Sci. Rep. 2018, 8, 850. [Google Scholar] [CrossRef] [PubMed]
- Williamson, J.R. Really exasperating viral protein from HIV. Elife 2015, 4. [Google Scholar] [CrossRef] [PubMed]
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).