Human parainfluenza virus type 1 C proteins are nonessential proteins that inhibit the host interferon and apoptotic responses and are required for efficient replication in nonhuman primates.
Recombinant human parainfluenza virus type 1 (rHPIV1) was modified to create rHPIV1-P(C-), a virus in which expression of the C proteins (C', C, Y1, and Y2) was silenced without affecting the amino acid sequence of the P protein. Infectious rHPIV1-P(C-) was readily recovered from cDNA, indicating that the four C proteins were not essential for virus replication. Early during infection in vitro, rHPIV1-P(C-) replicated as efficiently as wild-type (wt) HPIV1, but its titer subsequently decreased coincident with the onset of an extensive cytopathic effect not observed with wt rHPIV1. rHPIV1-P(C-) infection, but not wt rHPIV1 infection, induced caspase 3 activation and nuclear fragmentation in LLC-MK2 cells, identifying the HPIV1 C proteins as inhibitors of apoptosis. In contrast to wt rHPIV1, rHPIV1-P(C-) and rHPIV1-C(F170S), a mutant encoding an F170S substitution in C, induced interferon (IFN) and did not inhibit IFN signaling in vitro. However, only rHPIV1-P(C-) induced apoptosis. Thus, the anti-IFN and antiapoptosis activities of HPIV1 were separable: both activities are disabled in rHPIV1-P(C-), whereas only the anti-IFN activity is disabled in rHPIV1-C(F170S). In African green monkeys (AGMs), rHPIV1-P(C-) was considerably more attenuated than rHPIV1-C(F170S), suggesting that disabling the anti-IFN and antiapoptotic activities of HPIV1 had additive effects on attenuation in vivo. Although rHPIV1-P(C-) protected against challenge with wt HPIV1, its highly restricted replication in AGMs and in primary human airway epithelial cell cultures suggests that it might be overattenuated for use as a vaccine. Thus, the C proteins of HPIV1 are nonessential but have anti-IFN and antiapoptosis activities required for virulence in primates.
Bartlett
Emmalene J
EJ
Laboratory of Infectious Diseases, Respiratory Viruses Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, U.S. Department of Health and Human Services, Bethesda, Maryland 20892-8007, USA.
Cruz
Ann-Marie
AM
Esker
Janice
J
Castaño
Adam
A
Schomacker
Henrick
H
Surman
Sonja R
SR
Hennessey
Margaret
M
Boonyaratanakornkit
Jim
J
Pickles
Raymond J
RJ
Collins
Peter L
PL
Murphy
Brian R
BR
Schmidt
Alexander C
AC
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D006801:Humans; D007372:Interferons / Q000037:antagonists & inhibitors*; D008969:Molecular Sequence Data; D010222:Parainfluenza Virus 1, Human / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic; D014709:Vero Cells; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication / Q000187:drug effects*
D010750:Phosphoproteins; D014764:Viral Proteins; C068855:P protein, parainfluenza virus 1; C068856:C protein, human parainfluenza virus type 1; D007372:Interferons; D053148:Caspase 3