Avian Influenza Virus Infection of Immortalized Human Respiratory Epithelial Cells Depends upon a Delicate Balance between Hemagglutinin Acid Stability and Endosomal pH

Daidoji, Tomo; Watanabe, Yohei; Ibrahim, Madiha S.; Yasugi, Mayo; Maruyama, Hisataka; Masuda, Taisuke; Arai, Fumihito; Ohba, Tadashi; Honda, Ayae; Ikuta, Kazuyoshi; Nakaya, Takaaki

doi:10.1074/jbc.m114.611327

Cited by 30 publications

(52 citation statements)

References 68 publications

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“…First, the kinetics of acidification and the levels of pH in the endosomal compartment may vary depending on host species, target tissue, cell type, and differentiation and metabolic state of the cell. A balance between endosomal pH in the cells and pH optimum of HA conformational transition was shown to affect the efficiency of viral infection (20,28,60). Differences in sensitivity of viruses to ammonium chloride during cell entry (Table 1) well illustrate this phenomenon.…”

Section: Discussionmentioning

confidence: 80%

“…Limited available data on fusion pH and stability of influenza viruses circulating in natural host species seem to indicate that human viruses fuse at a lower pH than avian and swine viruses (21,(26)(27)(28)(29)(30). However, different viral strains and distinctive assays were used by different authors, and pronounced subtype-and staindependent variation in the viral fusion activity was observed in these studies hampering solid conclusions.…”

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confidence: 64%

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H1N1 Swine Influenza Viruses Differ from Avian Precursors by a Higher pH Optimum of Membrane Fusion

Baumann

Kouassi

Foni

et al. 2016

J Virol

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The H1N1 Eurasian avian-like swine (EAsw) influenza viruses originated from an avian H1N1 virus. To characterize potential changes in the membrane fusion activity of the hemagglutinin (HA) during avian-to-swine adaptation of the virus, we studied EAsw viruses isolated in the first years of their circulation in pigs and closely related contemporary H1N1 viruses of wild aquatic birds. Compared to the avian viruses, the swine viruses were less sensitive to neutralization by lysosomotropic agent NH 4 Cl in MDCK cells, had a higher pH optimum of hemolytic activity, and were less stable at acidic pH. Eight amino acid substitutions in the HA were found to separate the EAsw viruses from their putative avian precursor; four substitutions-T49 2 S, N72 2 D, R75 2 K, and S113 2 F-were located in the structural regions of the HA2 subunit known to play a role in acid-induced conformational transition of the HA. We also studied low-pH-induced syncytium formation by cell-expressed HA proteins and found that the HAs of the 1918, 1957, 1968, and 2009 pandemic viruses required a lower pH for fusion induction than did the HA of a representative EAsw virus. Our data show that transmission of an avian H1N1 virus to pigs was accompanied by changes in conformational stability and fusion promotion activity of the HA. We conclude that distinctive host-determined fusion characteristics of the HA may represent a barrier for avian-to-swine and swine-to-human transmission of influenza viruses. IMPORTANCEContinuing cases of human infections with zoonotic influenza viruses highlight the necessity to understand which viral properties contribute to interspecies transmission. Efficient binding of the HA to cellular receptors in a new host species is known to be essential for the transmission. Less is known about required adaptive changes in the membrane fusion activity of the HA. Here we show that adaptation of an avian influenza virus to pigs in Europe in 1980s was accompanied by mutations in the HA, which decreased its conformational stability and increased pH optimum of membrane fusion activity. This finding represents the first formal evidence of alteration of the HA fusion activity/stability during interspecies transmission of influenza viruses under natural settings.

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Section: Discussionmentioning

confidence: 80%

mentioning

confidence: 64%

H1N1 Swine Influenza Viruses Differ from Avian Precursors by a Higher pH Optimum of Membrane Fusion

Baumann

Kouassi

Foni

et al. 2016

J Virol

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“…Collectively, these three assays indicated that the HAs of Mem-H1N1 and the two duck IAVs, mal-H1N1 and mal-H2N2, underwent conformational transition and mediated membrane fusion at a lower pH than the HAs of VN-H5N1 and Sh-H7N9 (Table 1). Thus, the receptor binding properties of the recombinant IAVs and their relative pH optima of membrane fusion well represented typical properties of IAVs from corresponding natural reservoirs (aquatic birds, gallinaceous poultry, and humans) (19)(20)(21)(22)(34)(35)(36)(37)(38)(39).…”

Section: Resultsmentioning

confidence: 85%

“…The pH optimum of HA-mediated fusion of avian and mammalian IAVs varies depending on the host species and the history of virus evolution, and our study, for the first time, demonstrates that this variation influences viral sensitivity to IFN and IFITMs. Among different IAVs, human viruses typically have the lowest fusion pH optimum (from 5.0 to 5.4), whereas swine viruses and viruses of gallinaceous poultry, including high-and low-pathogenic IAVs of the H5 and H7 subtypes, display relatively high fusion pH optima (5.6 to 6.0) (22,24,(34)(35)(36)(37)(38)(39). IAVs isolated from wild aquatic birds appear to be particularly variable with respect to the fusion pH optimum (from 5.0 to 6.0), although available data are limited (22-24, 37, 38).…”

Section: Discussionmentioning

confidence: 99%

“…The optimal membrane fusion pH of IAV is thought to be determined by the interplay between two major hostdependent factors. First, studies of infection of cell cultures suggest that the viral fusion pH has to be compatible with the levels of acidification of the cellular endosomal compartment (37,(65)(66)(67). These levels may vary depending on the viral target cells and thus differ in airway epithelial cells of humans and pigs, intestinal epithelial cells of aquatic birds, and various types of cells during systemic infections of various species with highly pathogenic avian IAVs.…”

Section: Discussionmentioning

confidence: 99%

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pH Optimum of Hemagglutinin-Mediated Membrane Fusion Determines Sensitivity of Influenza A Viruses to the Interferon-Induced Antiviral State and IFITMs

Gerlach

Hensen

Matrosovich

et al. 2017

J Virol

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The replication and pathogenicity of influenza A viruses (IAVs) critically depend on their ability to tolerate the antiviral interferon (IFN) response. To determine a potential role for the IAV hemagglutinin (HA) in viral sensitivity to IFN, we studied the restriction of IAV infection in IFN-β-treated human epithelial cells by using 2:6 recombinant IAVs that shared six gene segments of A/Puerto Rico/8/1934 virus (PR8) and contained HAs and neuraminidases of representative avian, human, and zoonotic H5N1 and H7N9 viruses. In A549 and Calu-3 cells, viruses displaying a higher pH optimum of HA-mediated membrane fusion, H5N1-PR8 and H7N9-PR8, were less sensitive to the IFN-induced antiviral state than their counterparts with HAs from duck and human viruses, which fused at a lower pH. The association between a high pH optimum of fusion and reduced IFN sensitivity was confirmed by using HA point mutants of A/Hong Kong/1/1968-PR8 that differed solely by their fusion properties. Furthermore, similar effects of the viral fusion pH on IFN sensitivity were observed in experiments with (i) primary human type II alveolar epithelial cells and differentiated cultures of human airway epithelial cells, (ii) nonrecombinant zoonotic and pandemic IAVs, and (iii) preparations of IFN-α and IFN-λ1. A higher pH of membrane fusion and reduced sensitivity to IFN correlated with lower restriction of the viruses in MDCK cells stably expressing the IFN-inducible transmembrane proteins IFITM2 and IFITM3, which are known to inhibit viral fusion. Our results reveal that the pH optimum of HA-driven membrane fusion of IAVs is a determinant of their sensitivity to IFN and IFITM proteins. The IFN system constitutes an important innate defense against viral infection. Substantial information is available on how IAVs avoid detection by sensors of the IFN system and disable IFN signaling pathways. Much less is known about the ability of IAVs to tolerate the antiviral activity of IFN-induced cellular proteins. The IFN-induced proteins of the IFITM family block IAV entry into target cells and can restrict viral spread and pathogenicity. Here we show for the first time that the sensitivity of IAVs to the IFN-induced antiviral state and IFITM2 and IFITM3 proteins depends on the pH value at which the viral HA undergoes a conformational transition and mediates membrane fusion. Our data imply that the high pH optimum of membrane fusion typical of zoonotic IAVs of gallinaceous poultry, such as H5N1 and H7N9, may contribute to their enhanced virulence in humans.

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Demethylation around the transcriptional start site of the IFN-β gene induces IFN-β production and protection against influenza virus infection

Nishioka

Daidoji

Nakaya

2019

Biochemical and Biophysical Research Communications

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Avian Influenza Virus Infection of Immortalized Human Respiratory Epithelial Cells Depends upon a Delicate Balance between Hemagglutinin Acid Stability and Endosomal pH

Cited by 30 publications

References 68 publications

H1N1 Swine Influenza Viruses Differ from Avian Precursors by a Higher pH Optimum of Membrane Fusion

H1N1 Swine Influenza Viruses Differ from Avian Precursors by a Higher pH Optimum of Membrane Fusion

pH Optimum of Hemagglutinin-Mediated Membrane Fusion Determines Sensitivity of Influenza A Viruses to the Interferon-Induced Antiviral State and IFITMs

Demethylation around the transcriptional start site of the IFN-β gene induces IFN-β production and protection against influenza virus infection

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