Severe acute respiratory syndrome coronavirus protein 6 accelerates murine hepatitis virus infections by more than one mechanism.
The severe acute respiratory syndrome coronavirus (SARS-CoV) encodes numerous accessory proteins whose importance in the natural infection process is currently unclear. One of these accessory proteins is set apart by its function in the context of a related murine hepatitis virus (MHV) infection. SARS-CoV protein 6 increases MHV neurovirulence and accelerates MHV infection kinetics in tissue culture. Protein 6 also blocks nuclear import of macromolecules from the cytoplasm, a process known to involve its C-terminal residues interacting with cellular importins. In this study, protein 6 was expressed from plasmid DNAs and accumulated in cells prior to infection by wild-type MHV. Output of MHV progeny was significantly increased by preexisting protein 6. Protein 6 with C-terminal deletion mutations no longer interfered with nuclear import processes but still retained much of the capacity to augment MHV infections. However, some virus growth-enhancing activity could be ascribed to the C-terminal end of protein 6. To determine whether this augmentation provided by the C terminus was derived from interference with nuclear import, we evaluated the virus-modulating effects of small interfering RNAs (siRNAs) directed against importin-beta mRNAs, which down-regulated classical nuclear import pathways. The siRNAs did indeed prime cells for enhanced MHV infection. Our findings indicated that protein 6-mediated nuclear import blocks augmented MHV infections but is clearly not the only way that this accessory protein operates to create a milieu conducive to robust virus growth. Thus, the SARS-CoV protein 6 accelerates MHV infections by more than one mechanism.
Hussain
Snawar
S
Department of Microbiology and Immunology, Loyola University Medical Center, 2160 South First Avenue, Maywood, IL 60153, USA.
Perlman
Stanley
S
Gallagher
Thomas M
TM
D021581:Active Transport, Cell Nucleus; D002460:Cell Line; D018352:Coronavirus Infections / Q000821:virology*; D020868:Gene Silencing; D006801:Humans; D006517:Murine hepatitis virus / Q000254:growth & development* / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D045473:Severe acute respiratory syndrome-related coronavirus / Q000502:physiology*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D028961:beta Karyopherins / Q000037:antagonists & inhibitors
D034741:RNA, Small Interfering; D014764:Viral Proteins; D028961:beta Karyopherins; C507223:protein 6, SARS virus