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J. Virol., Dec 1995, 7688-7698, Vol 69, No. 12
MA Brooks, AN Ali, PC Turner and RW Moyer
Poxviruses are unique among viruses in encoding members of the serine
proteinase inhibitor (serpin) superfamily. Orthopoxviruses contain three
serpins, designated SPI-1, SPI-2, and SPI-3. SPI-1 encodes a 40- kDa
protein that is required for the replication of rabbitpox virus (RPV) in
PK-15 or A549 cells in culture (A. N. Ali, P. C. Turner, M. A. Brooks, and
R. W. Moyer, Virology 202:305-314, 1994). Examination of nonpermissive
human A549 cells infected with an RPV mutant disrupted in the SPI-1 gene
(RPV delta SPI-1) suggests there are no gross defects in protein or DNA
synthesis. The proteolytic processing of late viral structural proteins, a
feature of orthopoxvirus infections associated with the maturation of virus
particles, also appears relatively normal. However, very few mature virus
particles of any kind are produced compared with the level found in
infections with wild-type RPV. Morphological examination of RPV delta
SPI-1-infected A549 cells, together with an observed fragmentation of
cellular DNA, suggests that the host range defect is associated with the
onset of apoptosis. Apoptosis is seen only in RPV delta SPI-1 infection of
nonpermissive (A549 or PK-15) cells and is absent in all wild-type RPV
infections and RPV delta SPI-2 mutant infections examined to date. Although
the SPI-1 gene is expressed early, before DNA replication, the triggering
apoptotic event occurs late in the infection, as RPV delta SPI-1- infected
A549 cells do not undergo apoptosis when infections are carried out in the
presence of cytosine arabinoside. While the SPI-2 (crmA) gene, when
transfected into cells, has been shown to inhibit apoptosis, our
experiments provide the first indication that a poxvirus serpin protein can
inhibit apoptosis during a poxvirus infection.
Copyright © 1995, American Society for Microbiology
A rabbitpox virus serpin gene controls host range by inhibiting apoptosis in restrictive cells
Department of Molecular Genetics and Microbiology, College of Medicine, University of Florida, Gainesville 32610-0266, USA.
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