Inhibition of Xenotropic Murine Leukemia Virus-Related Virus by APOBEC3 Proteins and Antiviral Drugs

Abstract

Xenotropic murine leukemia virus-related virus (XMRV), a gammaretrovirus, has been isolated from human prostate cancer tissue and from activated CD4؉ T cells and B cells of patients with chronic fatigue syndrome, suggesting an association between XMRV infection and these two diseases. Since APOBEC3G (A3G) and APOBEC3F (A3F), which are potent inhibitors of murine leukemia virus and Vif-deficient human immunodeficiency virus type 1 (HIV-1), are expressed in human CD4؉ T cells and B cells, we sought to determine how XMRV evades suppression of replication by APOBEC3 proteins. We found that expression of A3G, A3F, or murine A3 in virus-producing cells resulted in their virion incorporation, inhibition of XMRV replication, and G-to-A hypermutation of the viral DNA with all three APOBEC3 proteins. Quantitation of A3G and A3F mRNAs indicated that, compared to the human T-cell lines CEM and H9, prostate cell lines LNCaP and DU145 exhibited 50% lower A3F mRNA levels, whereas A3G expression in 22Rv1, LNCaP, and DU145 cells was nearly undetectable. XMRV proviral genomes in LNCaP and DU145 cells were hypermutated at low frequency with mutation patterns consistent with A3F activity. XMRV proviral genomes were extensively hypermutated upon replication in A3G/A3F-positive T cells (CEM and H9), but not in A3G/A3F-negative cells (CEM-SS). We also observed that XMRV replication was susceptible to the nucleoside reverse transcriptase (RT) inhibitors zidovudine (AZT) and tenofovir and the integrase inhibitor raltegravir. In summary, the establishment of XMRV infection in patients may be dependent on infection of A3G/A3F-deficient cells, and cells expressing low levels of A3G/A3F, such as prostate cancer cells, may be ideal producers of infectious XMRV. Furthermore, the anti-HIV-1 drugs AZT, tenofovir, and raltegravir may be useful for treatment of XMRV infection.Gammaretroviruses infect a wide range of species and are associated with a variety of neurological and immunological disorders, as well as carcinomas and leukemias (9,11,21,30,58). In 2006, for the first time, a gammaretrovirus was isolated from human tissues and was named xenotropic murine leukemia virus-related virus (XMRV) (63). The virus was discovered to be prevalent in prostate cancer tissues derived from patients carrying a mutation in the RNASEL gene, an important player in the interferon-mediated suppression of viral infection in host target cells (48,53,54). A recent study found XMRV in several prostate cancer samples with the same prevalence for patients with and without the RNASEL mutation and suggested that XMRV infection may be associated with nearly 30% of all prostate cancers (51). However, two other studies could not confirm an association of XMRV with prostate cancer in Germany, suggesting that XMRV's geographic distribution may not extend to Europe (10,17). In addition to prostate cancers, XMRV was also recently isolated from chronic fatigue syndrome (CFS) patients, exhibiting a high prevalence of 67% in confirmed cases and a prevalence of 4% in healthy co...

No Evidence of Murine-Like Gammaretroviruses in CFS Patients Previously Identified as XMRV-Infected

“…3), most likely a reflection of the passage of XMRV through human cells, which renders the virus less sensitive to human complement (24)(25)(26). These results, as well as other reports showing restriction of XMRV replication in human cells (27,28), suggest that an established MLV infection in humans is unlikely.…”

Phylogenetic Analysis of Murine Leukemia Virus Sequences from Longitudinally Sampled Chronic Fatigue Syndrome Patients Suggests PCR Contamination Rather than Viral Evolution

“…It is therefore substantially more similar to XMRV than to either the polytropic or modified polytropic MLV sequences previously reported by Lo et al (17). There is no evidence for hypermutation mediated by APOBEC proteins in the patient-derived sequences as might be expected during an infection, given the susceptibility of MLV to mutation by these proteins (23). Thus, these new patient-derived MLV sequences show tremendous variation from the parental CFS type 1 sequence and as such are extremely unlikely to have evolved from the CFS type 1 sequence.…”

“…XMRV detection in a small percentage of samples from healthy controls suggested widespread infection (7,18,29). Controversy has since surrounded XMRV detection, partly because many laboratories have been unable to detect XMRV in patient samples (2, 5, 6, 8-11, 14, 16, 19-21, 28, 30, 35, 37, 40) and partly because an almost identical virus has been found infecting a common prostate cancer cell line called 22Rv1 (12,15,23). These data strongly suggest that XMRV in patient material is the result of DNA contamination from laboratory cell lines or mouse DNA.…”

Evaluation of Cellular Determinants Required for In Vitro Xenotropic Murine Leukemia Virus-Related Virus Entry into Human Prostate Cancer and Noncancerous Cells

“…The authors of these studies have proposed that the in vivo susceptibility to XMRV cannot be determined by the Xpr1 receptor expression alone but that the ability of different cell types to either transactivate the XMRV viral promoter or to restrict virus replication define how efficient the virus can spread in certain tissues (11). Recent studies have also shown that XMRV infectivity can be limited by the presence of known host restriction factors to retroviral replication, such as the human APOBEC3 and tetherin proteins, as well as mouse APOBEC3, tetherin, and Fv1 proteins (11,28). It is noteworthy that a number of human cells, including breast cells have been shown to be susceptible to infection by the mouse mammary tumor virus (MMTV) (13,14), in spite of the fact that the human orthologue of the murine transferrin receptor 1 (Trf1), which is the known cellular receptor for MMTV, is not able to support viral entry in human cells (32).…”