The polymerase acidic protein gene of influenza a virus contributes to pathogenicity in a mouse model.
Adaptation of influenza A viruses to a new host species usually involves the mutation of one or more of the eight viral gene segments, and the molecular basis for host range restriction is still poorly understood. To investigate the molecular changes that occur during adaptation of a low-pathogenic avian influenza virus subtype commonly isolated from migratory birds to a mammalian host, we serially passaged the avirulent wild-bird H5N2 strain A/Aquatic bird/Korea/W81/05 (W81) in the lungs of mice. The resulting mouse-adapted strain (ma81) was highly virulent (50% mouse lethal dose = 2.6 log(10) 50% tissue culture infective dose) and highly lethal. Nonconserved mutations were observed in six viral genes (those for PB2, PB1, PA, HA, NA, and M). Reverse genetic experiments substituting viral genes and mutations demonstrated that the PA gene was a determinant of the enhanced virulence in mice and that a Thr-to-Iso substitution at position 97 of PA played a key role. In growth kinetics studies, ma81 showed enhanced replication in mammalian but not avian cell lines; the PA(97I) mutation in strain W81 increased its replicative fitness in mice but not in chickens. The high virulence associated with the PA(97I) mutation in mice corresponded to considerably enhanced polymerase activity in mammalian cells. Furthermore, this characteristic mutation is not conserved among avian influenza viruses but is prevalent among mouse-adapted strains, indicating a host-dependent mutation. To our knowledge, this is the first study that the isoleucine residue at position 97 in PA plays a key role in enhanced virulence in mice and is implicated in the adaptation of avian influenza viruses to mammalian hosts.
Song
Min-Suk
MS
College of Medicine and Medical Research Institute, Chungbuk National University, Cheongju 361-763, Republic of Korea.
Pascua
Philippe Noriel Q
PN
Lee
Jun Han
JH
Baek
Yun Hee
YH
Lee
Ok-Jun
OJ
Kim
Chul-Joong
CJ
Kim
Hyunggee
H
Webby
Richard J
RJ
Webster
Robert G
RG
Choi
Young Ki
YK
D000220:Adaptation, Biological; D000818:Animals; D001715:Bird Diseases / Q000821:virology; D001717:Birds; D002460:Cell Line; D005818:Genetic Engineering; D053125:Influenza A Virus, H5N2 Subtype / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity*; D005585:Influenza in Birds / Q000821:virology; D007723:Korea; D007928:Lethal Dose 50; D008168:Lung / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D020125:Mutation, Missense; D009976:Orthomyxoviridae Infections / Q000821:virology; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics / Q000502:physiology*; D012692:Serial Passage; D016019:Survival Analysis; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*; D037521:Virulence Factors / Q000235:genetics / Q000502:physiology*
C061290:PA protein, influenza viruses; D014764:Viral Proteins; D037521:Virulence Factors; D012324:RNA-Dependent RNA Polymerase