[SIZE=-1]Journal of Virology, April 2011, p. 3179-3186, Vol. 85, No. 7[/SIZE] [SIZE=-1]0022-538X/11/$012.00+0 doi:10.1128/JVI.02333-10[/SIZE] [SIZE=-1]American Society for Microbiology. All Rights Reserved.[/SIZE] NF-B Activation Stimulates Transcription and Replication of Retrovirus XMRV in Human B-Lineage and Prostate Carcinoma Cells Shuhei Sakakibara,1* Kaori Sakakibara,2 and Giovanna Tosato1 Laboratory of Cellular Oncology,1 Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 208922 Received 8 November 2010/ Accepted 20 January 2011 Xenotropic murine leukemia virus-related virus (XMRV) is a gammaretrovirus linked to prostate carcinoma and chronic fatigue syndrome. Here we report that NF-B activation can markedly increase XMRV production. The inflammatory cytokine tumor necrosis factor alpha (TNF-), which activates NF-B, significantly augmented viral Gag protein production in XMRV-infected cells. Reporter assays showed that TNF- and Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1), an intrinsic NF-B activator, increased long terminal repeat (LTR)-dependent XMRV transcription. We identified two NF-B binding sites (designated B-1 and B-2) in the LTR U3 region of XMRV and demonstrated that both sites bind to the NF-B component p65/RelA. Mutation of the B-1 site, but not the B-2 site, impaired responsiveness to TNF- and LMP1 in reporter assays. A mutant XMRV with a mutation at the B-1 site replicated significantly less efficiently than the wild-type XMRV in the prostate carcinoma LNCaP, DU145, and PC-3 cell lines, HEK293 cells, the EBV-immortalized cell line IB4, and the Burkitt's lymphoma cell line BJAB. These results demonstrate that TNF- and EBV LMP1 enhance XMRV replication in prostate carcinoma and B-lineage cells through the B-1 site in the XMRV LTR, suggesting that inflammation, EBV infection, and other conditions leading to NF-B activation may promote XMRV spread in humans.