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Journal of Virology, October 2000, p. 8793-8802, Vol. 74, No. 19
Department of Microbiology and Immunology,
The University of Texas Medical Branch at Galveston, Galveston, Texas
77555-10191; Department of Microbiology
and Institute for Cellular and Molecular Biology, The University of
Texas at Austin, Austin, Texas 78712-10952; and
Department of Cancer Biology, Lerner Research Institute,
The Cleveland Clinic Foundation, Cleveland, Ohio
441953
Received 13 March 2000/Accepted 29 June 2000
We characterized a novel 28S rRNA cleavage in cells infected with
the murine coronavirus mouse hepatitis virus (MHV). The 28S rRNA
cleavage occurred as early as 4 h postinfection (p.i.) in
MHV-infected DBT cells, with the appearance of subsequent cleavage products and a decrease in the amount of intact 28S rRNA with increasing times of infection; almost all of the intact 28S rRNA disappeared by 24 h p.i. In contrast, no specific 18S rRNA
cleavage was detected in infected cells. MHV-induced 28S rRNA cleavage was detected in all MHV-susceptible cell lines and all MHV strains tested. MHV replication was required for the 28S rRNA cleavage, and
mature cytoplasmic 28S rRNA underwent cleavage. In certain combination
of cells and viruses, pretreatment of virus-infected cells with
interferon activates a cellular endoribonuclease, RNase L, that causes
rRNA degradation. No interferon was detected in the inoculum used for
MHV infection. Addition of anti-interferon antibody to MHV-infected
cells did not inhibit 28S rRNA cleavage. Furthermore, 28S rRNA cleavage
occurred in an MHV-infected mouse embryonic fibroblast cell line
derived from RNase L knockout mice. Thus, MHV-induced 28S rRNA cleavage
was independent of the activation of RNase L. MHV-induced 28S rRNA
cleavage was also different from apoptosis-related rRNA degradation,
which usually occurs concomitantly with DNA fragmentation. In
MHV-infected 17Cl-1 cells, 28S rRNA cleavage preceded DNA fragmentation
by at least 18 h. Blockage of apoptosis in MHV-infected 17Cl-1
cells by treatment with a caspase inhibitor did not block 28S rRNA
cleavage. Furthermore, MHV-induced 28S rRNA cleavage occurred in
MHV-infected DBT cells that do not show apoptotic signs, including
activation of caspase-3 and DNA fragmentation. Thus, MHV-induced 28S
rRNA cleavage appeared to differ from any rRNA degradation mechanism
described previously.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
RNase L-Independent Specific 28S rRNA Cleavage in
Murine Coronavirus-Infected Cells

*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, TX 77555-1019. Phone: (409) 772-2323. Fax: (409)
772-5065. E-mail: shmakino{at}utmb.edu.
Present address: Department of Microbiology and Immunology,
Stanford University, Stanford, CA 94305.
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