Xenotropic Murine Leukemia Virus-Related Virus Establishes an Efficient Spreading Infection and Exhibits Enhanced Transcriptional Activity in Prostate Carcinoma Cells

Abstract

Xenotropic murine leukemia virus-related virus (XMRV) is a novel human gammaretrovirus discovered in association with human prostate tumors. XMRV was first identified in prostate stromal cells surrounding the tumors of patients carrying a mutation in the HPC1 gene locus. To determine the tropism of XMRV in cell culture, we tested the ability of XMRV to spread and replicate in various prostate and nonprostate cell lines. We found that although the expression of XMRV viral proteins and the spread of infectious virus were minimal in a variety of cell lines, XMRV displayed robust expression and infection in LNCaP prostate tumor cells. The transcriptional activity of the XMRV long terminal repeat (LTR) was found to be higher than the Moloney murine leukemia virus LTRs in both LNCaP and WPMY-1 (simian virus 40-transformed prostate stromal cells). The U3 promoter of XMRV and a glucocorticoid response element (GRE) within the U3 were required for the transcriptional activity in LNCaP cells. Coexpression of the androgen receptor and stimulation with dihydrotestosterone stimulated XMRV-LTR-dependent transcription in 293T cells, and the GRE was required for this activity. These data suggest that XMRV may replicate more efficiently in LNCaP cells in part due to the transcriptional environment in LNCaP cells.Nearly 35% of familial prostate cancer patients carry a germ line mutation (R462Q) in the HPC1 gene locus (15). This locus encodes the protein RNase L, which is expressed and activated upon virus infection and degrades single-stranded viral and cellular RNA, thus blocking replication of the infecting virus and inducing apoptosis (1, 16). The association of prostate cancers with this variant of RNase L raised the possibility that mutant individuals were more susceptible to an unknown tumor virus (2, 15). Total polyadenylated RNA from prostate tumors that were either heterozygous or homozygous for the mutant RNase L allele was isolated and hybridized to a DNA microarray (Virochip) containing oligomers of ϳ950 viral genomes (19). Seven of eleven tumors that carried at least one allele of the RNase L mutation were positive for the novel retrovirus. Isolation and sequencing of the virus from three different prostate cancer patients revealed nucleotide similarities to xenotropic murine leukemia viruses (MLVs), and the virus was named xenotropic MLV-related virus (XMRV) (19). The genome structure of XMRV is typical of gamma retroviruses. The env gene encodes a glycoprotein homologous to the MLV envelope protein that mediates virus binding to the xenotropic receptor, XPR1, on the surface of cells (4). In contrast to more complex retroviruses such as lentiviruses, XMRV does not encode any accessory genes, nor does it encode any host-derived oncogenes (3). Fluorescence in situ hybridization and immunohistochemistry revealed that a small number of stromal cells surrounding the tumor, but not tumor cells themselves, were positive for XMRV nucleotide sequences and viral proteins, suggesting that XMRV maintains a low level of infectio...

No Evidence of Xenotropic Murine Leukemia Virus-Related Virus Transmission by Blood Transfusion from Infected Rhesus Macaques

“…The biological properties of XMRV indicate a broad host range and cell tropism, including human cell lines (26,27,52), and XMRV contamination was found in several cell lines used for research (52). These results emphasize the need to evaluate XMRV and other MLV contaminations in cell lines used in the laboratory and in the manufacture of biological products (32) as well as to minimize virus exposure to reduce the potential risk of human infection.…”

“…These findings have led to the general scientific consensus that XMRV is not a human retrovirus but a novel recombinant murine retrovirus with some unique biological properties (23). XMRV has a broad host range and can infect a variety of human cell lines in vitro (24)(25)(26)(27) and nonhuman primate cells and tissues in vivo (5,28). Studies of XMRV injection in rhesus macaques and pigtailed macaques along with a study of wild-derived Mus pahari mice (29) indicated that XMRV infection shows a transient acute phase of infection, during which time the virus was detected in peripheral blood cells.…”

Xenotropic Murine Leukemia Virus-Related Virus Proviral DNA Not Detected in Blood Samples Donated in Japan

“…Moreover, genomic sequences of XMRV were found in 0-3.7z of blood samples obtained from healthy populations (2,3). XMRV can be transmitted via activated lymphocytes and cell-free plasma of individuals who are diagnosed as virus positive by PCR analysis, and XMRV can replicate in prostate carcinoma cell lines (2,6). These findings indicate the possibility of viral transmission via blood transfusion, which poses a great threat.…”

The Glucocorticoid Receptor in Retroviral Infection

“…The ability of activated GR to block NFkB's transactivation of these genes is likely important in mediating the immunosuppressive effect of glucocorticoids (Ito et al, 2001). GRE are present in the genomes of most gamma-retroviruses (Bruland et al, 2003a, Rodriguez & Goff, 2010, Pages et al, 1995 and HIV-1 based lentiviruses (Ghosh, 1992;Mitra et al, 1995;Hapgood & Tomasicchio, 2010). NFkB response elements are generally absent in gamma-retroviruses, but present in HIV-1, making GR-mediated regulation of lentiviral vectors derived from the HIV-1 backbone more complex.…”