Showing papers on "Friend leukemia published in 1992"

Role of the PU.1 transcription factor in controlling differentiation of Friend erythroleukemia cells.

Abstract: Both viral and cellular genes have been directly implicated in pathogenesis of Friend viral erythroleukemia. The virus-encoded gp55 glycoprotein binds to erythropoietin receptors to cause mitogenesis and differentiation of erythroblasts. However, if the provirus integrates adjacent to the gene for the PU.1 transcription factor, the cell loses its commitment to terminally differentiate and becomes immortal, as indicated by its transplantability and by its potential for indefinite growth in culture (C. Spiro, B. Gliniak, and D. Kabat, J. Virol. 63:4434-4437, 1989; R. Paul, S. Schuetze, S. L. Kozak, and D. Kabat, J. Virol. 65:464-467, 1991). To test the implications of these results, we produced polyclonal antiserum to bacterially synthesized PU.1, and we used it to analyze PU.1 expression throughout leukemic progression and during chemically induced differentiation of Friend erythroleukemia (F-MEL) cell lines. This antiserum identified three electrophoretically distinct PU.1 components in extracts of F-MEL cells and demonstrated their nuclear localization. Although PU.1 proteins are abundant in F-MEL cells, they are absent or present in only trace amounts in normal erythroblasts or in differentiating erythroblasts from the preleukemic stage of Friend disease. Furthermore, chemicals (dimethyl sulfoxide or N,N'-hexamethylenebisacetamide) that overcome the blocked differentiation of F-MEL cells induce rapid declines of PU.1 mRNA and PU.1 proteins. The elimination of PU.1 proteins coincides with recommitment to the program of erythroid differentiation and with loss of immortality. These results support the hypothesis that PU.1 interferes with the commitment of erythroblasts to differentiate and that chemicals that reduce PU.1 expression reinstate the erythropoietic program.

Molecular characterization of a neuropathogenic and nonerythroleukemogenic variant of Friend murine leukemia virus PVC-211

Abstract: PVC-211 murine leukemia virus (MuLV) is a replication-competent, ecotropic type C retrovirus that was isolated after passage of the Friend virus complex through F344 rats. Unlike viruses in the Friend virus complex, it does not cause erythroleukemia but causes a rapidly progressive hind limb paralysis when injected into newborn rats and mice. We have isolated an infectious DNA clone (clone 3d) of this virus which causes neurological disease in animals as efficiently as parental PVC-211 MuLV. The restriction map of clone 3d is very similar to that of the nonneuropathogenic, erythroleukemogenic Friend murine leukemia virus (F-MuLV), suggesting that PVC-211 MuLV is a variant of F-MuLV and that no major structural alteration was involved in its derivation. Studies with chimeric viruses between PVC-211 MuLV clone 3d and wild-type F-MuLV clone 57 indicate that at least one determinant for neuropathogenicity resides in the 2.1-kb XbaI-ClaI fragment containing the gp70 coding region of PVC-211 MuLV. Compared with nonneuropathogenic ecotropic MuLVs, the env gene of PVC-211 MuLV encodes four unique amino acids in the gp70 protein. Nucleotide sequence analysis also revealed a deletion in the U3 region of the long terminal repeat (LTR) of PVC-211 MuLV clone 3d compared with F-MuLV clone 57. In contrast to the env gene of PVC-211 MuLV, particular sequences within the U3 region of the viral LTR do not appear to be required for neuropathogenicity. However, the changes in the LTR of PVC-211 MuLV may be responsible for the failure of this virus to cause erythroleukemia, because chimeric viruses containing the U3 region of F-MuLV clone 57 were erythroleukemogenic whereas those with the U3 of PVC-211 MuLV clone 3d were not.

Mutations in the env gene of friend spleen focus-forming virus overcome Fv-2r-mediated resistance to Friend virus-induced erythroleukemia.

Abstract: Although Fv-2r homozygous mice are resistant to leukemias induced either by an erythropoietin-encoding virus or by wild-type Friend virus (FV) (M. E. Hoatlin, S. L. Kozak, F. Lilly, A. Chakraborti, C. A. Kozak, and D. Kabat, Proc. Natl. Acad. Sci. USA 87:9985-9989, 1990), they are susceptible to some variants of FV (R. A. Steeves, E. A. Mirand, A. Bulba, and P. J. Trudel, Int. J. Cancer 5:349-356, 1970; R. W. Geib, M. B. Seaward, M. L. Stevens, C.-L. Cho, and M. Majumdar, Virus Res. 14:161-174, 1989). To localize the virus gene involved in influencing the host range, we cloned and sequenced the env gene of the BB6 variant of FV (Steeves et al., Int. J. Cancer 5:349-356, 1970). In comparison with the wild-type env gene, the BB6 variant contains a 159-bp deletion that eliminates the membrane-proximal portion of the extracellular domain and 58 point mutations resulting in 13 amino acid changes. Substitution of the variant env gene for the wild-type env gene resulted in a recombinant virus that produced a Friend virus-like disease in Fv-2r homozygotes. Our results identify the spleen focus-forming virus env gene as the viral gene involved in this virus-host interaction. Additionally, they suggest that the product of the Fv-2r gene modifies the interaction between the spleen focus-forming virus envelope protein and the erythropoietin receptor.

Inhibition of Friend leukemia cell visceral metastases by a new monoclonal antibody and role of the immune system of the host in its action

Abstract: We developed a syngeneic mouse IgG2a monoclonal antibody (MAb) A9D41 directed against the Friend leukemia virus envelope gp70 antigen present on the cell surface membranes of virus producer 3Cl8 Friend leukemia cells (FLC). A9D41 showed a marked antitumor activity in DBA/2 mice given injections of gp70 positive 3Cl8 FLC, but it was ineffective in mice given injections of gp70 negative 745 FLC or unrelated tumor cells. A9D41 was particularly effective in inhibiting the development of 3Cl8 FLC liver and spleen metastases. MAb was also effective as adjuvant therapy in inhibiting visceral metastases after excision of an established s.c. FLC tumor, and combined therapy of A9D41 with mouse interferon α/β was more effective than MAb or interferon α/β alone. The immune system of the host played a decisive role in the antimetastatic action of A9D41. Thus, although MAb was cytotoxic for 3Cl8 FLC in vitro in the presence of rabbit complement, the F(ab9)2 fragment was ineffective in vivo, and the antitumor effect of MAb was abolished in mice treated with an antibody to CD4 and diminished in natural killer cell-deficient beige and athymic nude mice. MAb-treated mice surviving injection of FLC developed an immune response to 3Cl8 FLC.

Identification of multi-drug resistant cells in sensitive Friend leukemia cells by quantitative videomicrofluorimetry.

Abstract: The cellular resistance to cytotoxic drugs, particularly to anthracyclines, remains a major problem in cancer chemotherapy. A number of biochemical mechanisms have been described, one of them being a lower accumulation of drugs in resistant cells. The accumulation of Ho33342 in sensitive and resistant Friend leukemia cells was studied by quantitative fluorescence image analysis, a method which allows investigations to be made on living tissues and cells. The intensity of fluorescence is related to the amount of Ho33342 accumulated into the cells and has been found to be more intense in sensitive cells than in resistant ones. Moreover, the retention of this vital dye was inversely related to the degree of resistance in the three resistant cell lines. The addition of verapamil, which is known to reverse resistance to anthracyclines, resulted in an increase of the amount of Ho33342 accumulated in the resistant cells. Ho33342 presents a higher quantum yield than any other anthracyclines, such as adriamycin and can be used as a microfluorimetric probe to identify the resistant cells in a heterogeneous cell population.

Selection of a new multidrug resistant cell line from Friend leukemia cells by short and cyclic exposures to high concentrations of daunorubicin.

Abstract: BACKGROUND Resistance of tumor cells to cytotoxic agents can be due to the overexpression of the mdr 1 gene, which encodes a plasma membrane protein (P-glycoprotein). To understand the molecular basis of multidrug resistance, several laboratories have isolated cell lines resistant to doxorubicin, actinomycin D, vinca alkaloids and related agents. Many months or years of culture with gradually increasing concentrations of cytotoxic agents are necessary to obtain a resistant cell line. METHODS We selected a new multidrug resistant cell line (MELC-DRTL) by 24-hour cycles of exposure to relatively high concentrations of daunorubicin from sensitive Friend Leukemia cells. After each cycle, the residual live cells were expanded up to the density of 1 x 10(6) cells/ml. RESULTS The assay conducted with MoAb C-219 showed a high expression on the membrane surface of P-glycoprotein in the MELC-DRTL line, but the fact that it was impossible to obtain a complete reversal of the resistance, even when using high concentrations of verapamil, suggests the presence of other mechanisms unrelated to the presence of P-glycoprotein. CONCLUSIONS The kind of cellular resistance induction used in this experiment enabled us to obtain an MDR cell line in three months of culture.

Retroviral Insertions Downstream oftheHeterogeneous Nuclear Ribonucleoprotein AlGeneinErythroleukemia Cells: Evidence that AlIsNotEssential forCellGrowth

Abstract: A large numberofnovel cellular proto-oncogenes havebeenidentified andcloned byanalysis ofcommon integration sites inretrovirally induced malignancies. Inthemultistage erythroleukemias induced bythe various strains ofFriend leukemia virus, theanalysis ofproviral-integration events hasledtotheidentification oftwogenes, Fli-1 andSpi-1, bothnovel membersoftheetsoncogene family oftranscription factors. Inthis report, wedescribe theidentification ofanother integration site, designated Fli-2 (Friend leukemia virus integration-2), inanerythroleukemia celllineinduced byFriendmurineleukemia virus(F-MuLV). Rearrangements attheFli-2 locus werefoundintwoerythroleukemia cell lines independently induced by F-MuLVandoneleukemic cell line derived fromthespleen ofamouseinfected withthepolycythemia strain ofFriend leukemia virus. Thededuced aminoacidsequence ofa cDNAcorresponding toa transcript originating fromgenomic DNA adjacent toFli-2 isidentical tothatofthehumanheterogeneous nuclear ribonucleoprotein Algene, amemberofthegenefamily ofRNA-binding proteins involved inRNA splicing. Inoneerythroleukemia cell line, Alexpression wasundetectable asaresult ofF-MuLVintegration inoneallele andloss oftheother allele. These results suggest that perturbations inRNAsplicing mechanisms maycontribute tomalignant transformation andprovide direct evidence that theAlprotein isnotrequired forcell growth. Friend leukemia isa multistage malignancy associated withanearly stage characterized bythepolyclonal proliferation ofinfected erythroid progenitors followed byaleukemicstage inwhicherythroleukemia cell clones emerge(2, 17). Theearly andlate stages ofFriend leukemia canbe induced following asingle injection ofeither thepolycythemia-oranemia-inducing strain ofFriend leukemia virus (FV-PorFV-A,respectively). BothFV-PandFV-Aare complexes of a defective spleenfocus-forming virus (SFFV-P andSFFV-A,respectively) andareplication-competent Friend murineleukemia virus (F-MuLV). F-MuLV itself canalsoinduce erythroleukemia wheninjected into newborn miceofcertain susceptible strains (34). We havepreviously shownthat thetumorsuppressor gene p53isinactivated inalmost alloftheerythroleukemia cell lines induced byvarious strains ofFriend leukemia virus, as aresult ofdeletion, truncation, retrovirus insertion, orpoint mutation (2, 27,28). Moreau-Gachelin etal.haveidentified a commonsite forretroviral integration namedSpi-1 (SFFV provirus integration-1) andshownthatthislocusisrearranged inthemajority oftheerythroleukemia celllines induced bytheFV-PandFV-Astrains ofFriend leukemia virus (24, 25). DNA sequences whoseexpression ishighly activated asaresult oftheseSFFVinsertions havebeen isolated- immediately adjacent totheSpi-1 insertion sites (26). Thesequence ofSpi-1 transcripts isidentical tothat of PU.1,agenethat encodes aDNA-binding protein related to