Infectivity and insertional mutagenesis of endogenous retrovirus in autoimmune NZB and B/W mice.

Murine leukaemia virus has been suggested to contribute to both autoimmune disease and leukaemia in the NZB mouse and in the (NZB × NZW) F1 (abbreviated B/W) mouse. However, with apparently only xenotropic but no ecotropic virus constitutively expressed in these mice, few mechanisms could explain the aetiology of either disease in either mouse strain. Because pseudotyped and/or inducible ecotropic virus may play a role, we surveyed the ability of murine leukaemia virus in NZB, NZW and B/W mice to infect and form a provirus. From the spleen of NZB mice, we isolated circular cDNA of xenotropic and polytropic virus, which indicates ongoing infection by these viruses. From a B/W lymphoma, we isolated and determined the complete sequence of a putative ecotropic NZW virus. From B/W mice, we recovered de novo endogenous retroviral integration sites (tags) from the hyperproliferating cells of the spleen and the peritoneum. The tagged genes seemed to be selected to aid cellular proliferation, as several of them are known cancer genes. The insertions are consistent with the idea that endogenous retrovirus contributes to B-cell hyperproliferation and progression to lymphoma in B/W mice.

APOBEC3 enzymes restrict marginal zone B cells.

In general, a long-lasting immune response to viruses is achieved when they are infectious and replication competent. In the mouse, the neutralizing antibody response to Friend murine leukemia virus is contributed by an allelic form of the enzyme Apobec3 (abbreviated A3). This is counterintuitive because A3 directly controls viremia before the onset of adaptive antiviral immune responses. It suggests that A3 also affects the antibody response directly. Here, we studied the relative size of cell populations of the adaptive immune system as a function of A3 activity. We created a transgenic mouse that expresses all seven human A3 enzymes and compared it to WT and mouse A3-deficient mice. A3 enzymes decreased the number of marginal zone B cells, but not the number of follicular B or T cells. When mouse A3 was knocked out, the retroelement hitchhiker-1 and sialyl transferases encoded by genes close to it were overexpressed three and two orders of magnitude, respectively. We suggest that A3 shifts the balance, from the fast antibody response mediated by marginal zone B cells with little affinity maturation, to a more sustained germinal center B-cell response, which drives affinity maturation and, thereby, a better neutralizing response.

An autoimmune disease prevented by anti-retroviral drugs.

BACKGROUND: Both Aicardi-Goutières syndrome, a Mendelian mimic of congenital infection, and the autoimmune disease systemic lupus erythematosus can result from mutations in the gene encoding the enzyme Trex1. In mice, the absence of Trex1 causes severe myocarditis. The enzyme is thought to degrade endogenous retroelements, thus linking them to autoimmune disease. However, inhibition of reverse transcription by the inhibitor zidovudine (AZT) did not ameliorate the disease, weakening the link to retroelements. FINDINGS: Here, we show that two other FDA-approved drugs that inhibit reverse transcriptase can ameliorate the myocarditis in Trex1-null mouse. CONCLUSIONS: The result suggests that retroelements contribute to this hereditary form of autoimmunity, and that treatment with retroelement inhibitors might ameliorate Aicardi-Goutières syndrome in humans.

Orphan receptor GPR110, an oncogene overexpressed in lung and prostate cancer.

BACKGROUND: GPR110 is an orphan G protein-coupled receptor--a receptor without a known ligand, a known signaling pathway, or a known function. Despite the lack of information, one can assume that orphan receptors have important biological roles. In a retroviral insertion mutagenesis screen in the mouse, we identified GPR110 as an oncogene. This prompted us to study the potential isoforms that can be gleaned from known GPR110 transcripts, and the expression of these isoforms in normal and transformed human tissues. METHODS: Various epitope-tagged isoforms of GPR110 were expressed in cell lines and assayed by western blotting to determine cleavage, surface localization, and secretion patterns. GPR110 transcript and protein levels were measured in lung and prostate cancer cell lines and clinical samples, respectively, by quantitative PCR and immunohistochemistry. RESULTS: We found four potential splice variants of GPR110. Of these variants, we confirmed three as being expressed as proteins on the cell surface. Isoform 1 is the canonical form, with a molecular mass of about 100 kD. Isoforms 2 and 3 are truncated products of isoform 1, and are 25 and 23 kD, respectively. These truncated isoforms lack the seven-span transmembrane domain characteristic of GPR proteins and thus are not likely to be membrane anchored; indeed, isoform 2 can be secreted. Compared with the median gene expression of approximately 200 selected genes, GPR110 expression was low in most tissues. However, it had higher than average gene expression in normal kidney tissue and in prostate tissues originating from older donors. Although identified as an oncogene in murine T lymphomas, GPR110 is greatly overexpressed in human lung and prostate cancers. As detected by immunohistochemistry, GPR110 was overexpressed in 20 of 27 (74%) lung adenocarcinoma tissue cores and in 17 of 29 (59%) prostate adenocarcinoma tissue cores. Additionally, staining with a GPR110 antibody enabled us to differentiate between benign prostate hyperplasia and potential incipient malignancy. CONCLUSION: Our work suggests a role for GPR110 in tumor physiology and supports it as a potential therapeutic candidate and disease marker for both lung and prostate cancer.

Early onset of autoimmune disease by the retroviral integrase inhibitor raltegravir.

Raltegravir is a recently, Food and Drug Administration-approved, small-molecule drug that inhibits retroviral integrase, thereby preventing HIV DNA from inserting itself into the human genome. We report here that the activity profile of raltegravir on the replication of murine leukemia virus is similar to that for HIV, and that the drug specifically affects autoimmune disease in mice, in which endogenous retroelements are suspected to play a role. While NZW and BALB/c mice, which do not succumb to autoimmune disease, are not affected by raltegravir, lupus-prone (NZBxNZW) F(1) mice die of glomerulonephritis more than a month earlier than untreated mice. Raltegravir-treated NZB mice, which share the H-2 haplotype with BALB/c mice, but which are predisposed to autoimmune hemolytic anemia, develop auto-antibodies to their red blood cells >3 months earlier than untreated mice of the same strain. Because nonautoimmune mice are not affected by raltegravir, we consider off-target effects unlikely and attribute the exacerbation of autoimmunity to the inhibition of retroviral integrase.

Pvt1-encoded microRNAs in oncogenesis.

BACKGROUND: The functional significance of the Pvt1 locus in the oncogenesis of Burkitt's lymphoma and plasmacytomas has remained a puzzle. In these tumors, Pvt1 is the site of reciprocal translocations to immunoglobulin loci. Although the locus encodes a number of alternative transcripts, no protein or regulatory RNA products were found. The recent identification of non-coding microRNAs encoded within the PVT1 region has suggested a regulatory role for this locus. RESULTS: The mouse Pvt1 locus encodes several microRNAs. In mouse T cell lymphomas induced by retroviral insertions into the locus, the Pvt1 transcripts, and at least one of their microRNA products, mmu-miR-1204 are overexpressed. Whereas up to seven co-mutations can be found in a single tumor, in over 2,000 tumors none had insertions into both the Myc and Pvt1 loci. CONCLUSION: Judging from the large number of integrations into the Pvt1 locus - more than in the nearby Myc locus - Pvt1 and the microRNAs encoded by it are as important as Myc in T lymphomagenesis, and, presumably, in T cell activation. An analysis of the co-mutations in the lymphomas likely place Pvt1 and Myc into the same pathway.