Genetic and Microenvironmental Effects on Friend Murine Leukemia Virus-induced Erythroleukemia
Keywords: Friend murine leukemia virus
Erythroleukemia

Both tissue microenvironment and genetic changes are involved in development of cancer. We employed the Friend murine leukemia virus (F-MuLV)- induced erythroleukemia model to study the role of these parameters in induction of malignancy. The tissue microenvironment is composed of non-cellular and cellular components. In regards to the non-cellular part, we previously reported that vascular endothelial growth factor (VEGF), in combination with macrophage chemoattractant protein-5, contributes to leukemia progression in F-MuLV- infected mice. To study the influence of constitutively elevated VEGF levels on the progression of erythroleukemia, we inoculated VEGF hi/+ mice, which are heterozygous for a VEGF “hypermorphic” allele, with F-MuLV. Unexpectedly, a significant delay in erythroleukemia was observed in these mice when compared with wild-type controls. The VEGF hi/+ mice exhibited a higher natural killer (NK) cell activity, elevated B cells, and a decrease in T-cell number. Furthermore, higher erythroid progenitors (i.e. CD34+, CD36+, and TER119+ cells) were evident in the bone marrow, spleen, and peripheral blood of these mice. Also, the CFU-E levels were significantly elevated in VEGF hi/+ bone marrow cultures. We propose that a compensatory erythropoietic response combined with increased NK cell activity account for the extended survival of erythroleukemic, VEGF hi/+mice. In regards to the cellular component of tissue microenvironment we studied the role of B cells in response to F-MuLV. To test the hypothesis that virus- neutralizing antibodies are involved in providing sterilizing immunity to F-MuLV we inoculated adult female mice with F-MuLV so that their newborns are provided with anti-viral antibodies. F-MuLV challenge of these newborns did not lead to induction of erythroleukemia. Conversely, mice from a control group (newborns whose mother had not received viral inoculation) contracted erythroleukemia upon F-MuLV challenge, as shown by hepatosplenomegaly, anemia, and emergence of leukemic cells in the spleen. These results indicated the importance of anti-viral antibodies in immunity to F-MuLV and suggested that anti-F-MuLV antibodies were generated in mothers, transferred to their offspring and protected them from viral challenge. The key genetic event upon F-MuLV infection is viral integration at the Fli-1 locus. We set to identify F-MuLV integration sites in SCID mice following two observations that these mice show a delay in induction of leukemia and also they do not exhibit viral integration at the Fli-1 locus. We hypothesized that development of leukemia in these mice is due to F-MuLV integration at a region other than the Fli-1 locus. Using a GenomeWalking approach we identified a total of 15 viral integration sites in F-MuLV-infected SCID mice, with eight of them interrupting the following genes: Mex3d, Fam125b, Prdm16, Rhoq, Ahdc1, Zc3h4, Msh3, and Hcls1. Using PCR to amplify the virus- host DNA junction fragment we found that one of the viral insertion sites (chromosome 10; position 20,942,825) occurs with a frequency of 35 % and therefore is considered as a common integration site.