Class II polytropic murine leukemia viruses (MuLVs) of AKR/J mice: possible role in the generation of class I oncogenic polytropic MuLVs

Mixed retroviral infections frequently exhibit pseudotyping, in which the genome of one virus is packaged in a virion containing SU proteins encoded by another virus. Infection of mice by Moloney murine leukemia virus (M-MuLV), which induces lymphocytic leukemia, results in a mixed viral infection composed of the inoculated ecotropic M-MuLV and polytropic MuLVs generated by recombination of M-MuLV with endogenous retroviral sequences. In this report, we describe pseudotyping which occurred among the polytropic and ecotropic MuLVs in M-MuLV-infected mice. Infectious center assays of polytropic MuLVs released from splenocytes or thymocytes of infected mice revealed that polytropic MuLVs were extensively pseudotyped within ecotropic virions. Late in the preleukemic stage, a dramatic change in the extent of pseudotyping occurred in thymuses. Starting at about 5 weeks, there was an abrupt increase in the number of thymocytes that released nonpseudotyped polytropic viruses. A parallel increase in thymocytes that released ecotropic M-MuLV packaged within polytropic virions was also observed. Analyses of the clonality of preleukemic thymuses and thymomas suggested that the change in pseudotyping characteristics was not the result of the emergence of tumor cells. Examination of mice infected with M-MuLV, Friend erythroleukemia virus, and a Friend erythroleukemia virus-M-MuLV chimeric virus suggested that the appearance of polytropic virions late in the preleukemic stage correlated with the induction of lymphocytic leukemia. We discuss different ways in which pseudotypic mixing may facilitate leukemogenesis, including a model in which the kinetics of thymic infection, modulated by pseudotyping and viral interference, facilitates a stepwise mechanism of leukemogenesis.

Section: Detection Of Polytropic Mulvs From M-mulv-infected Animals Wmentioning

confidence: 99%

A multistep process of leukemogenesis in Moloney murine leukemia virus-infected mice that is modulated by retroviral pseudotyping and interference

Lavignon

Evans

1996

“…More recent studies demonstrate that the LTR functions to determine the leukemogenic potential of the viruses in vivo by mediating the rate of infection of the bursal target stem cell (2). The timing of infection of thymocytes appears to affect the acceleration of leukemia in AKR mice as well (16).…”

Section: Fragmentmentioning

confidence: 99%

“…Mink cell focus-forming (MCF) retroviruses have been implicated as the proximal leukemogenic agents in the induction of spontaneous leukemia in certain inbred strains of mice (19,21,23,34). MCF viruses have been isolated from the thymus and other tissues of AKR mice during the preleukemic period (9, 10,15,16). Some MCF isolates when injected into newborn animals accelerate the onset of leukemia (10,34).…”

mentioning

confidence: 99%

Influence of enhancer sequences on thymotropism and leukemogenicity of mink cell focus-forming viruses

Holland

Thomas

Chattopadhyay

et al. 1989

Oncogenic mink cell focus-forming (MCF) viruses, such as MCF 247, show a positive correlation between the ability to replicate efficiently in the thymus and a leukemogenic phenotype. Other MCF viruses, such as MCF 30-2, replicate to high titers in thymocytes and do not accelerate the onset of leukemia. We used these two MCF viruses with different biological phenotypes to distinguish the effect of specific viral genes and genetic determinants on thymotropism and leukemogenicity. Our goal was to identify the viral sequences that distinguish thymotropic, nonleukemogenic viruses such as MCF 30-2 from thymotropic, leukemogenic viruses such as MCF 247. We cloned MCF 30-2, compared the genetic hallmarks of MCF 30-2 with those of MCF 247, constructed a series of recombinants, and tested the ability of the recombinant viruses to replicate in the thymus and to induce leukemia. The results established that (i) MCF 30-2 and MCF 247 differ in the numbers of copies of the enhancer sequences in the long terminal repeats. (ii) The thymotropic phenotype of both viruses is independent of the number of copies of the enhancer sequences. (iii) The oncogenic phenotype of MCF 247 is correlated with the presence in the virus of duplicated enhancer sequences or with the presence of an enhancer with a specific sequence. These results show that the pathogenic phenotypes of MCF viruses are dissociable from the thymotropic phenotype and depend, at least in part, upon the enhancer sequences. On the basis of these results, we suggest that the molecular mechanisms by which the enhancer sequences determine thymotropism are different from those that determine oncogenicity.

“…MCF virus recombinants whose env sequences originate from an Mpmv endogenous virus have been reported (18,80). However, while MCF virus recombinants generated by other MuLV strains (e.g., Friend MuLV) frequently contain Mpmv-derived env sequences, most M-MuLV-derived MCF viruses contain Pmv-derived env (18). Thus, the lack of detection of MCF proviruses in In the initial screen, a second tumor with the same pattern of LOH as tumor 50 was identified.…”

Section: Resultsmentioning

confidence: 99%

Low-frequency loss of heterozygosity in Moloney murine leukemia virus-induced tumors in BRAKF1/J mice

Lander

Fan

1997

To identify potential involvement of tumor suppressor gene inactivation during leukemogenesis by Moloney murine leukemia virus (M-MuLV), a genome-wide scan for loss of heterozygosity (LOH) in tumor DNAs was made. To assess LOH, it is best to study mice that are heterozygous at many loci across the genome. Accordingly, we generated a collection of 52 M-MULV-induced tumor DNAs from C57BR/cdJ ؋ AKR/J F 1 (BRAKF1) hybrid mice. By using direct hybridization with oligonucleotides specific for three different classes of endogenous MuLV-related proviruses, 48 markers on 16 of 19 autosomes were simultaneously examined for allelic loss. No allelic losses were detected, with the exception of a common loss of markers on chromosome 4 in two tumors. The three autosomes that lacked informative endogenous proviral markers were also analyzed for LOH by PCR with simple-sequence length polymorphisms (SSLPs); one additional tumor showed LOH on chromosome 15. Further screening with chromosome 4 SSLPs identified one additional tumor with LOH on chromosome 4. Therefore, in total, the average fractional allelic loss was quite low (0.002), but the LOH frequency of 6% on chromosome 4 was highly statistically significant (P < 0.0005). Detailed SSLP mapping of the three tumors with LOH on chromosome 4 localized the region of common LOH to the distal 45 centimorgans, a region syntenic with human chromosomes 1 and 9. Candidate tumor suppressor genes, Mts1 (p16 INK4a ) and Mts2 (p15 INK4b ), have been mapped to this region, but by Southern blot analysis, no homozygous deletions were detected in either gene. One of three tumors with LOH on chromosome 4 also showed a proviral insertion near the c-myc proto-oncogene. These results suggested that tumor suppressor inactivation is generally infrequent in M-MuLV-induced tumors but that a subset of these tumors may have lost a tumor suppressor gene on chromosome 4. MATERIALS AND METHODSMice. C57BR/cdJ females and AKR/J males were purchased from the Jackson Laboratory (Bar Harbor, Maine). BRAKF1 mice were derived by crossing female C57BR/cdJ mice with male AKR/J mice.Virus and inoculation of BRAKF1 mice. Viral stocks were clarified cell culture supernatants derived from NIH 3T3 fibroblasts productively infected with wildtype M-MuLV; portions of viral stocks were individually frozen at Ϫ70ЊC and were thawed and used only once (22). Virus infectivity titrations were performed by the UV-XC syncytial assay (69). BRAKF1 mice were inoculated intraperitoneally with 0.15 ml of virus stock (2 ϫ 10 4 XC PFU) within 48 h of birth.Tumor purification and DNA isolation. Moribund M-MuLV-infected BRAKF1 mice were sacrificed, and thymic tumor tissue was removed and rinsed gently with phosphate-buffered saline. Tumor cells were recovered by mincing the tumor in phosphate-buffered saline and passing the homogenate through a