Is the optimal pH for membrane fusion in host cells by avian influenza viruses related to host range and pathogenicity?

Okamatsu, Masatoshi; Motohashi, Yurie; Hiono, Takahiro; Tamura, Tomokazu; Nagaya, Kazuki; Matsuno, Keita; Sakoda, Yoshihiro; Kida, Hiroshi

doi:10.1007/s00705-016-2902-z

Cited by 9 publications

(9 citation statements)

References 29 publications

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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%

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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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Section: Resultsmentioning

confidence: 85%

Section: Discussionmentioning

confidence: 99%

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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“…Recent reports, including our own, have shown that the acid stability of the H5N1 HA protein is more vulnerable to pH (i.e., the pH threshold of H5N1 viruses is higher) than that of non-zoonotic AIVs [34,[65][66][67][68][69][70][71]. After viral internalization via endocytosis, this biochemical property (i.e., acid stability) of H5N1 may support infectivity as shown by the results in human tracheal (present results) and bronchiolar (previous results) epithelial cells [34].…”

Section: Discussionmentioning

confidence: 81%

Infection of Human Tracheal Epithelial Cells by H5 Avian Influenza Virus Is Regulated by the Acid Stability of Hemagglutinin and the pH of Target Cell Endosomes

Daidoji

Kajikawa

Arai

et al. 2020

Viruses

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Despite the possible relationships between tracheal infection and concomitant infection of the terminal part of the lower respiratory tract (bronchioles/alveoli), the behavior of avian influenza viruses (AIVs), such as H5N1, in the conducting airways is unclear. To examine the tropism of AIVs for cells lining the conducting airways of humans, we established human tracheal epithelial cell clones (HTEpC-Ts) and examined their susceptibility to infection by AIVs. The HTEpC-Ts showed differing susceptibility to H5N1 and non-zoonotic AIVs. Viral receptors expressed by HTEpC-Ts bound all viruses; however, the endosomal pH was associated with the overall susceptibility to infection by AIVs. Moreover, H5N1 hemagglutinin broadened viral tropism to include HTEpC-Ts, because it had a higher pH threshold for viral–cell membrane fusion. Thus, H5N1 viruses infect human tracheal epithelial cells as a result of their higher pH threshold for membrane fusion which may be one mechanism underlying H5N1 pathogenesis in human airway epithelia. Efficient replication of H5N1 in the conducting airways of humans may facilitate infection of the lower respiratory tract.

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“…After receptor-mediated endocytosis of the incoming virion along the endosomal pathway, the cleaved HA is subjected to a continuous pH decrease until an irreversible conformational change takes place that enables fusion of the membranes from the virion and endosome (9,33,34). A mild acidic fusion activation pH is common to HPAIV, in contrast to LPAIV (54), and regulates high virulence in chicken (37). In our study, we found that in R65, each of these two HA residues, 123R and 124I, is crucial for an elevated HA fusion activation pH.…”

Section: Discussionmentioning

confidence: 99%

“…Eventually, 138N (154N) complemented the whole set of all six key positions in the 2000 HPAIV (Table 3). Because several cell lines and tissues display different final (minimum) pH in their endosomes (78,79), they may not be permissible to influenza virus infection if the required HA fusion activation pH of a particular strain is lower than the endosomal endpoint pH, as is the case with LPAIV (54,78). Therefore, an increased acid sensitivity of the HA activating fusion competence enables the virus to infect cells with a milder acidic final pH in their endosomes, resulting in extended cell tropism (78,79).…”

Section: Discussionmentioning

confidence: 99%

A Dual Motif in the Hemagglutinin of H5N1 Goose/Guangdong-Like Highly Pathogenic Avian Influenza Virus Strains Is Conserved from Their Early Evolution and Increases both Membrane Fusion pH and Virulence

Wessels

Mostafa

Veits

et al. 2018

J Virol

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Zoonotic highly pathogenic avian influenza viruses (HPAIV) have raised serious public health concerns of a novel pandemic. These strains emerge from low-pathogenic precursors by the acquisition of a polybasic hemagglutinin (HA) cleavage site, the prime virulence determinant. However, required coadaptations of the HA early in HPAIV evolution remained uncertain. To address this question, we generated several HA1/HA2 chimeras and point mutants of an H5N1 clade 2.2.2 HPAIV and an H5N1 low-pathogenic strain. Initial surveys of 3,385 HPAIV H5 HA sequences revealed frequencies of 0.5% for the single amino acids 123R and 124I but a frequency of 97.5% for the dual combination. This highly conserved dual motif is still retained in contemporary H5 HPAIV, including the novel H5NX reassortants carrying neuraminidases of different subtypes, like the H5N8 and the zoonotic H5N6 strains. Remarkably, the earliest Asian H5N1 HPAIV, the Goose/Guangdong strains from 1996/1997, carried 123R only, whereas 124I appeared later in 1997. Experimental reversion in the HPAIV HA to the two residues 123S and124T, characteristic of low-pathogenic strains, prevented virus rescue, while the single substitutions attenuated the virus in both chicken and mice considerably, accompanied by a decreased HA fusion pH. This increased pH sensitivity of H5 HPAIV enables HA-mediated membrane fusion at a higher endosomal pH. Therefore, this HA adaptation may permit infection of cells with less-acidic endosomes, e.g., within the respiratory tract, resulting in an extended organ tropism. Taken together, HA coadaptation to increased acid sensitivity promoted the early evolution of H5 Goose/Guangdong-like HPAIV strains and is still required for their zoonotic potential. Zoonotic highly pathogenic avian influenza viruses (HPAIV) have raised serious public health concerns of a novel pandemic. Their prime virulence determinant is the polybasic hemagglutinin (HA) cleavage site. However, required coadaptations in the HA (and other genes) remained uncertain. Here, we identified the dual motif 123R/124I in the HA head that increases the activation pH of HA-mediated membrane fusion, essential for virus genome release into the cytoplasm. This motif is extremely predominant in H5 HPAIV and emerged already in the earliest 1997 H5N1 HPAIV. Reversion to 123S or 124T, characteristic of low-pathogenic strains, attenuated the virus in chicken and mice, accompanied by a decreased HA activation pH. This increased pH sensitivity of H5 HPAIV extends the viral tropism to cells with less-acidic endosomes, e.g., within the respiratory tract. Therefore, early HA adaptation to increased acid sensitivity promoted the emergence of H5 Goose/Guangdong-like HPAIV strains and is required for their zoonotic potential.

show abstract

Is the optimal pH for membrane fusion in host cells by avian influenza viruses related to host range and pathogenicity?

Cited by 9 publications

References 29 publications

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

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

Infection of Human Tracheal Epithelial Cells by H5 Avian Influenza Virus Is Regulated by the Acid Stability of Hemagglutinin and the pH of Target Cell Endosomes

A Dual Motif in the Hemagglutinin of H5N1 Goose/Guangdong-Like Highly Pathogenic Avian Influenza Virus Strains Is Conserved from Their Early Evolution and Increases both Membrane Fusion pH and Virulence

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