Inhibition of AKR leukemogenesis by SMX-1, a dualtropic murine leukemia virus

Prostate cancer progression correlates with increased humoral immune response to a human endogenous retrovirus GAG protein

PURPOSE

Human endogenous retroviruses (HERV) encode 8% of the human genome. While HERVs may play a role in autoimmune and neoplastic disease, no mechanistic association has yet been established. We studied the expression and immunogenicity of a HERV-K GAG protein encoded on chromosome 22q11.23 in relation to the clinical course of prostate cancer.

EXPERIMENTAL DESIGN

In vitro expression of GAG-HERV-K was analyzed in panels of normal and malignant tissues, microarrays, and cell lines, and effects of demethylation and androgen stimulation were evaluated. Patient sera were analyzed for seroreactivity to GAG-HERV-K and other self-antigens by ELISA and seromics (protein array profiling).

RESULTS

GAG-HERV-K expression was most frequent in prostate tissues and regulated both by demethylation of the promoter region and by androgen stimulation. Serum screening revealed that antibodies to GAG-HERV-K are found in a subset of patients with prostate cancer (33 of 483, 6.8%) but rarely in male healthy donors (1 of 55, 1.8%). Autoantibodies to GAG-HERV-K occurred more frequently in patients with advanced prostate cancer (29 of 191 in stage III-IV, 21.0%) than in early prostate cancer (4 of 292 in stages I-II, 1.4%). Presence of GAG-HERV-K serum antibody was correlated with worse survival of patients with prostate cancer, with a trend for faster biochemical recurrence in patients with antibodies to GAG-HERV-K.

CONCLUSIONS

Preferential expression of GAG-HERV-K ch22q11.23 in prostate cancer tissue and increased frequency of autoantibodies observed in patients with advanced prostate cancer make this protein one of the first bona fide retroviral cancer antigens in humans, with potential as a biomarker for progression and biochemical recurrence rate of prostate cancer. Clin Cancer Res; 19(22); 6112-25. ©2013 AACR.

The pathophysiology of murine retrovirus-induced leukemias

Murine leukemia viruses (MuLVs) are retroviruses which induce a broad spectrum of hematopoietic malignancies. In contrast to the acutely transforming retroviruses, MuLVs do not contain transduced cellular genes, or oncogenes. Nonetheless, MuLVs can cause leukemias quickly (4 to 6 weeks) and efficiently (up to 100% incidence) in susceptible strains of mice. The molecular basis of MuLV-induced leukemia is not clear. However, the contribution of individual viral genes to leukemogenesis can be assayed by creating novel viruses in vitro using recombinant DNA techniques. These genetically engineered viruses are tested in vivo for their ability to cause leukemia. Leukemogenic MuLVs possess genetic sequences which are not found in nonleukemogenic viruses. These sequences control the histologic type, incidence, and latency of disease induced by individual MuL Vs.

SMX-1 virus-induced inhibition of ecotropic and recombinant proviral sequence amplification in thymuses of AKR mice

SMX-1 virus delays the appearance of spontaneous thymomas in AKR mice which have been inoculated as young adults by the intrathymic route. Analyses of high-molecular-weight thymus DNAs from SMX-1 virus-inoculated AKR mice indicated the absence of 3' recombinant proviral-cellular DNA junction fragments generated by EcoRI and PvuII digestion. An average of five recombinant proviral fragments were detected in DNAs from spontaneous thymomas that developed in medium-injected control mice. Preleukemic mice that amplify murine leukemia virus-related antigens on their thymocyte surface contained unintegrated proviruses in their thymus DNAs, and 2.3-kilobase EcoRI and 2.1-kilobase PvuII recombinant DNA fragments were detected.

Protection from spontaneous lymphoma development in SJL/J(v+) mice neonatally injected with dualtropic SJL-151 virus

In previous studies dualtropic type C retroviruses were isolated from spontaneous B-cell lymphomas that appear with a high incidence in SJL/J(v+) mice. In this report the possible in vivo pathogenic effect of one cloned dualtropic isolate, designated SJL-151, was investigated. SJL/J(v+) and CBA/J mice, neonatally injected with SJL-151 alone or in combination with SJL-ecotropic virus, were initially studied for virus recovery 4-8 weeks after infection by spleen cell cocultivation with mouse SC-1 and mink ML indicator cells. Whereas ecotropic virus was easily detected in treated mice, dualtropic virus was recovered only from the spleen cells of animals coinfected with SJL-ecotropic and SJL-151 viruses. With a panel of monoclonal antibodies the recovered dualtropic viruses showed an antigenic profile similar to that of the originally injected SJL-151 virus. Whereas virus-injected mice did not show lymphoma induction or acceleration, a remarkable decrease in spontaneous lymphoma incidence was observed in the SJL/J(v+) mice receiving SJL-151 virus alone. A virus-specific antibody response was detectable in these mice, but a similar serum reactivity was also demonstrated in SJL/J(v+) mice coinfected with SJL-ecotropic virus and SJL-151 virus, which subsequently developed lymphomas with the usual high incidence, thus rendering an antibody-mediated protective mechanism untenable. The possibility of viral interference, as an alternative mechanism for lymphoma prevention, is discussed in view of the findings that persistence of SJL-151 virus or de novo generation of dualtropic virus did not occur in aged SJL/J(v+) mice injected neonatally with SJL-151 virus alone.

Leukemogenesis by Gross passage A murine leukemia virus: expression of viruses with recombinant env genes in transformed cells

Gross passage A murine leukemia virus (MuLV) derived from extracts of C3Hf/Bi mouse leukemias has been shown to be a virus complex consisting of ecotropic, xenotropic, and recombinant, dualtropic MuLV components. The three virus components were distinguished biochemically by differences in the molecular weights and peptide maps of their primary env gene products synthesized in infected cells in vivo and in vitro. Virus expression was studied in primary leukemias induced in C3Hf/Bi mice by Gross passage A virus extracts and by the individual ecotropic and recombinant MuLV components that were isolated in vitro. Our findings suggest that expression of the recombinant MuLV component of the Gross passage A virus complex is necessary and sufficient for the induction of leukemias in C3Hf/Bi mice. In contrast, induction of leukemias by the ecotropic virus component appears to involve generation of a second virus with characteristics of recombinant, dualtropic MuLV.

Friend murine leukemia virus-induced leukemia is associated with the formation of mink cell focus-inducing viruses and is blocked in mice expressing endogenous mink cell focus-inducing xenotropic viral envelope genes

In these studies, we have shown data that are consistent with the hypothesis that mink cell focus-inducing viruses (MCF) play an important role in the generation of an erythroproliferative disease developing after injection of certain strains of newborn mice with ecotropic Friend murine leukemia virus (F-MuLV). Resistance to this disease is correlated with the endogenous expression of an MCF/xenotropic virus-gp70-related protein that may interfere with the replication or spread of MCF viruses. These ideas are supported by the following observations: (a) after infection with F-MuLV, only 6/13 strains of mice-developed disease, and studies with crosses between susceptible and resistant strains indicated that resistance was dominant. Although F-MuLV was shown to replicate equally well in all strains tested, viruses coding for MCF-specific viral envelope proteins could be detected only in the spleens of mice from strains that were resistant to F-MuLV-induced disease and not in the spleens of mice from strains that were resistant to F-MuLV-induced disease; (b) a Friend MCF (Fr-MCF) virus isolated from the spleen of an F-MuLV-infected mouse from a susceptible strain induced the same erythroproliferative disease when injected as an appropriate pseudotype into mice from susceptible but not resistant strains of mice; and (c) resistant but not susceptible strains of mice endogenously express MCF/xenotropic virus-related envelope glycoproteins that may be responsible for resistance by blocking receptors for MCF viruses. These results not only indicate that Fr-MCF virus is a crucial intermediate in the induction of disease by F-MuLV, but also suggest that a novel gene, either an MCF/xenotropic virus-related envelope gene or a gene controlling its expression, is responsible for resistance to erythroleukemia induced by F-MuLV.