The role of vesicular stomatitis virus matrix protein in inhibition of host-directed gene expression is genetically separable from its function in virus assembly

Abstract

Recently, the vesicular stomatitis virus matrix (M) protein has been shown to be capable of inhibition of host cell-directed transcription in the absence of other viral components (B. L. Black and D. S. Lyles, J. Virol. 66:4058-4064, 1992). M protein is a major structural protein that is known to play a critical role in virus assembly by binding the helical ribonucleoprotein core of the virus to the cytoplasmic surface of the cell plasma membrane during budding. In this study, two M protein mutants were tested to determine whether the inhibition of host transcription by M protein is an indirect effect of its function in virus assembly or whether it represents an independent function of M protein. The mutant M protein of the conditionally temperature sensitive (ts) vesicular stomatitis virus mutant, ts082, was found to be defective in its ability to inhibit host-directed gene expression, as shown by its inability to inhibit expression of a cotransfected target gene encoding chloramphenicol acetyltransferase. The ability of the ts082 M protein to function in virus assembly was similar to that of wild-type M protein, as shown by its ability to complement the group III ts M protein mutant, tsO23. Another mutant, MN1, which lacks amino acids 4 to 21 of M protein demonstrated that the abilities of M protein to inhibit chloramphenicol acetyltransferase gene expression and to localize to the nucleus were unaffected by deletion of this lysine-rich amino-terminal region but that the ability to function in virus assembly was ablated. Thus, the two M protein mutants examined in this study exhibited complementary phenotypes: ts082 M protein functioned in virus assembly but was defective in inhibition of host-directed gene expression, while MN1 M protein functioned in inhibiting gene expression but was unable to function in virus assembly. These data demonstrate that the role of M protein in inhibition of host transcription can be separated genetically from its role in virus assembly. Vesicular stomatitis virus (VSV), the prototype rhabdovirus, causes a rapid and potent cytopathic effect (CPE) (1, 35, 37). Among other effects, VSV infection results in inhibition of transcription and translation of host gene products. Recently, the viral matrix (M) protein has been shown to be capable of causing some of the cytopathic effects characteristic of VSV infection. M protein is a major structural protein that is known to play a critical role in virus assembly by binding the helical ribonucleoprotein core of the virus to the cytoplasmic surface of the cell plasma membrane during budding. In addition to its role in virus assembly, M protein has been shown to induce the rounding of polygonal cells that occurs during VSV infection (3). Furthermore, using an assay in which an M gene expression vector was cotransfected with a vector encoding the target gene, that for chloramphenicol acetyltransferase (CAT), expression of M protein was shown to inhibit host cell-directed transcription of the CAT gene in the absence of any other viral compone...

hnRNPs Relocalize to the Cytoplasm following Infection with Vesicular Stomatitis Virus

“…To determine whether the relocalization of hnRNPA1 is correlated with the ability of VSV to shut off host gene expression, cells were infected with the rwt and M protein mutant (rM51R-M) viruses. These viruses are isogenic except for a point mutation in the M protein of the rM51R-M virus which renders this virus defective in the inhibition of host transcription (7). At 6 h postinfection, the cells were analyzed by confocal microscopy in order to visualize the subcellular localization of hnRNPA1.…”

“…M protein also plays a major role in virus assembly. The function of M protein in virus assembly is genetically separable from its function in inhibiting host gene expression (7). M protein lacks any known enzymatic activity and may inhibit host gene expression by binding directly to host factors and inhibiting their function.…”

Interplay between Innate Immunity and Negative-Strand RNA Viruses: towards a Rational Model

“…5). This activity is genetically separable from its role in virus structure and assembly as shown by M mutants that are selectively defective (5,22,75,78). When expressed alone by transfection, M protein inhibits transcription by all three host RNA polymerases (3) and the nuclear-cytoplasmic transport of host RNA (102,294).…”

Inhibition of nucleo-cytoplasmic trafficking by RNA viruses: targeting the nuclear pore complex

“…Genetically these different roles of the M protein in VSV infection can be separated. Mutations in M that disrupt assembly do not prevent inhibition of transcription, while mutations that prevent inhibition of host cell gene expression do not affect assembly (Black et al, 1993;Coulon et al, 1990). In addition to these functions, expression of the M protein has been shown to inhibit a variety of nucleocytoplasmic trafficking pathways.…”