Resistance of paramyxoviridae to type I interferon-induced Bos taurus Mx1 dynamin.

Typical targets of type I interferon (IFN)-induced antiviral Mx proteins known to date have been shown to share a common profile: single-stranded negative-sense RNA viruses. Among them, human MxA is known to interfere with the replication of measles, human, and bovine parainfluenza-3 viruses (BoPi3V), that is, three members of the Paramyxoviridae family. Recently, bovine Mx1 protein (BoMx1) was included in the group of Mx proteins with authenticated antiviral potential, as it dramatically represses the replication of vesicular stomatitis virus (VSV). As replication in bovine cells of Pi3, respiratory syncytial (RS), and Sendai (Se) viruses, all members of the same family, is known to be reduced on IFN-alpha incorporation into the culture medium, it was hypothesized that the BoMx1 pathway possibly was involved, its antiviral spectrum thus probably extending to Paramyxoviridae. In this study, probing of BoMx1-inhibiting effects was carried out by infecting a transgenic Vero cell line that allows tightly regulated conditional expression of BoMx1 after doxycycline treatment with a wide array of Paramyxoviridae. Expressing and nonexpressing cells displayed similar viability, cytopathic effects (CPEs), and amounts of infectious virus yields, whatever the infecting virus or the multiplicity of infection (moi) imposed. It is, therefore, concluded that BoMx1 does not interfere with Paramyxoviridae.

Conditional expression of type I interferon-induced bovine Mx1 GTPase in a stable transgenic vero cell line interferes with replication of vesicular stomatitis virus.

In some vertebrate species, type I interferon(IFN)-induced Mx gene expression has been shown to confer resistance to some single-stranded RNA (ssRNA) viruses in vitro. Because the bovine species is subject to an exceptionally wide array of infections caused by such viruses, it is anticipated that an antiviral allele should have been retained by evolution at the bovine Mx locus. The identification of such allele may help in evaluating the real significance of the Mx genotype for disease resistance in vivo, in deciphering host-virus molecular interactions involved, or in improving innate disease resistance of livestock through marker-assisted selection. We validated a double transgenic Vero cell clone in which the bovine Mx1 reference allele is placed under control of the human cytomegalovirus (CMV) enhancer-promoter sequence containing elements from the bacterial tetracycline resistance operon to regulate transcription. In the selected clone, transgene repression was very tight, and derepression by doxycycline led to homogeneous 48-h duration expression of physiologic levels of bovine Mx1. Expression of the transgene caused a dramatic decrease in cytopathic efficiency and a 500-5000-fold yield reduction of the Indiana and New Jersey serotypes of vesicular stomatitis virus (VSV). To our knowledge, the transgenic clone developed here is the first ever reported that allows conditional expression of an Mx protein, thus providing a valuable tool for studying functions of Mx proteins in general and that of bovine Mx1 in particular. This latter may henceforward be included in the group of Mx proteins with authenticated anti-VSV activity, which offers new research avenues into the field of host-virus interactions.

Genomic structure, organisation, and promoter analysis of the bovine (Bos taurus) Mx1 gene.

Some MX proteins are known to confer a specific resistance against a panel of single-stranded RNA viruses. Many diseases due to such viruses are known to affect cattle worldwide, raising the possibility that the identification of an antiviral isoform of a bovine MX protein would allow the implementation of genetic selection programs aimed at improving innate resistance of cattle. With this potential application in mind, the present study was designed to isolate the bovine Mx1 gene including its promoter region and to investigate its genomic organisation and promoter reactivity. The bovine Mx1 gene is made up of 15 exons. All exon-intron boundaries conformed to the consensus sequences. A PCR product that contained a approximately 1-kb, 5'-flanking region upstream from the putative transcription start site was sequenced. Unexpectedly, this DNA region did not contain TATA or CCAAT motifs. A computer scan of the region disclosed a series of putative binding sites for known cytokines and transcription factors. There was a GAAAN(1-2)GAAA(C/G) motif, typical of an interferon-sensitive responsive element, between -118 and -107 from the putative transcription start site. There were also a NF-kappaB, two interleukin-6 binding sites, two Sp1 sites and five GC-rich boxes. The region also contained 12 stretches of the GAAA type, as described in all IFN-inducible genes. Bovine Mx1 expression was assessed by Northern blotting and immunofluorescence in the Madin Darby bovine kidney cells (MDBK) cell line treated with several stimuli. In conclusion, the bovine Mx1 gene and promoter region share the major structural and functional characteristics displayed by their homologs described in the rainbow trout, chicken, mouse and man.