Showing papers on "Friend leukemia published in 1990"

Friend spleen focus-forming virus induces factor independence in an erythropoietin-dependent erythroleukemia cell line.

Abstract: Erythroid cells from mice infected with the polycythemia-inducing strain of Friend spleen focus-forming virus (SFFVP), unlike normal erythroid cells, can proliferate and differentiate in apparent absence of the erythroid hormone erythropoietin (Epo). The unique envelope glycoprotein encoded by SFFV has been shown to be responsible for this biological effect. The recent isolation of an Epo-dependent erythroleukemia cell line, HCD-57, derived from a mouse infected at birth with Friend murine leukemia virus, afforded us the opportunity to study the direct effect of SFFVP on a homogeneous population of factor-dependent cells. The introduction of SFFVP in complex with various helper viruses into these Epo-dependent cells efficiently and reproducibly gave rise to lines which expressed high levels of SFFV and were factor independent. SFFV appears to be unique in its ability to abrogate the factor dependence of Epo-dependent HCD-57 cells, since infection of these cells with retroviruses carrying a variety of different oncogenes had no effect. The induction of Epo independence by SFFV does not appear to involve a classical autocrine mechanism, since there is no evidence that the factor-independent cells synthesize or secrete Epo or depend on it for their growth. However, the SFFV-infected, factor-independent cells had significantly fewer receptors available for binding Epo than their factor-dependent counterparts had, raising the possibility that the induction of factor independence by the virus may be due to the interaction of an SFFV-encoded protein with the Epo receptor.

Structural specificity for biological activity of trichostatin A, a specific inhibitor of mammalian cell cycle with potent differentiation-inducing activity in Friend leukemia cells.

Abstract: Biological activities of four chemically synthesized trichostatin-related compounds, (R)-trichostatin A, (S)-trichostatin A, (R)-trichostatic acid, and (S)-trichostatic acid, were investigated. Assays of differentiation-inducing activity in Friend leukemia cells and G2-arresting activity in the cell cycle of normal rat fibroblast cells were used as monitoring systems for comparing the bioactivities of these compounds. The results clearly showed that both of the enantiomers of trichostatic acid had no activity in both the assay systems. In the case of (S)-trichostatin A, the antipode of naturally occurring trichostatin A, 50% effective concentrations were determined to be 50-70-fold higher than those of (R)-trichostatin A. The relationship between this ratio and the value of enantiomeric excess strongly suggests that (S)-trichostatin A is also biologically inactive. These results indicate that the absolute configuration and the presence of the hydroxamate group of trichostatin A are essential for its biological activity.

Inactivation of the cellular p53 gene is a common feature of Friend virus-induced erythroleukemia: relationship of inactivation to dominant transforming alleles

Abstract: The Friend erythroleukemia virus complex contains no cell-derived oncogene. Transformation by this virus may therefore involve mutations affecting cellular gene expression. We provide evidence that inactivating mutations of the cellular p53 gene are a common feature in Friend virus-induced malignancy, consistent with an antioncogene role for p53 in this disease. We have shown that frequent rearrangements of the p53 gene cause loss of expression or synthesis of truncated proteins, whereas overexpression of p53 protein is seen in other Friend cell lines. We now demonstrate that p53 expression in the latter cells is also abnormal, as a result of missense mutations in regions encoding highly conserved amino acids. Three of these aberrant alleles obtained from cells from different mice were cloned and found to function as dominant oncogenes in gene transfer assays, supporting the view that certain naturally occurring missense mutations in p53 confer a dominant negative phenotype on the encoded protein.

Spi-1 oncogene activation in Rauscher and Friend murine virus-induced acute erythroleukemias.

Abstract: The Friend viruses, like the Rauscher virus, cause murine acute erythroleukemias which evolve in a similar multistep process. In previous studies it has been described that the late malignant proerythroblastic transformation induced by the polycythemia-inducing strain of Friend spleen focus-forming virus (SFFVP) is correlated with Spi-1 oncogene activation by insertional mutagenesis. In this paper we report that Spi-1 genomic rearrangements were also observed in 90% of tumors induced by the anemia-inducing strain of Friend spleen focus-forming virus (SFFVA) and in all Rauscher-induced tumors analyzed. SFFVA and Rauscher proviral insertions occurred in the viral integration cluster previously characterized in SFFVP-induced tumors. The Spi-1 1.4-Kb messenger RNA was found highly expressed in all SFFVA and Rauscher-induced malignant cells as compared to normal tissues. The nucleotide sequence of Spi-1 cDNA isolated from a library constructed from SFFVA-induced tumor cells revealed no difference between the Spi-1 gene transcripts expressed in both SFFVP and SFFVA-induced leukemic cells. These results indicate that Spi-1 gene activation is a general feature in the malignant proerythroblastic transformation which occurs in mice infected with Friend and Rauscher viruses.

Rearrangements of the Pim-1, c-myc, and p53 genes in Friend helper virus-induced mouse erythroleukemias.

Abstract: The Friend helper leukemia virus (F-MuLV) induces in mice leukemias of the erythroid, lymphoid, and myeloblastic lineages. Erythroleukemic cell DNAs were examined for genetic alterations at loci described as common proviral integration regions in MuLV-induced myeloid or lymphoid leukemias or in Friend complex-induced erythroleukemias. No alteration of the Fim-1, Fim-2, Fim-3, pvt-1, and Spi-1 loci were detected in 17 erythroleukemias, p53 gene rearrangement was observed in 6 (30%) erythroleukemias and was always associated with a loss of the germ line allele. Interestingly, genetic alterations were also detected at two loci, c-myc and Pim-1, previously described as common provirus integration regions in T lymphoid leukemias. Rearrangements of these two genes were often associated with p53 gene alteration within the same tumor.

Insertional inactivation of the p53 gene during friend leukemia: a new strategy for identifying tumor suppressor genes.

Abstract: Rearrangements within the p53 gene are observed in a high proportion of independent erythroleukemic cell lines derived from the spleens of mice infected with Friend leukemia virus. The majority of cells with at least one rearranged p53 allele do not express detectable levels of p53 protein. Here, we show that in 4 out of 19 newly established erythroleukemic cell lines induced by infecting DBA mice with either the anemia (FV-A) or polycythemia (FV-P)-inducing strains of Friend virus, the p53 gene is rearranged as a result of integration of spleen focus-forming virus (SFFV). Integration of SFFV within the p53 gene resulted in inactivation of gene expression as determined by Western blot analysis. The sites of SFFV integration in the p53 gene were found, by Southern blot analysis and the polymerase chain reaction, to be localized in a 1-kbp region between introns 7 and 9. In addition, loss of the normal p53 allele was observed in three of the erythroleukemic cell lines that carried a rearranged p53 gene. Insertion of SFFV in these cell lines resulted in either the appearance of aberrant p53 transcripts or the complete lack of p53 expression. The results presented in this paper demonstrate that retroviral insertions can not only contribute to neoplastic transformation by activating dominant oncogenes but also by inactivating genes that normally function in a negative way to control cell growth. Thus, it may be possible to identify additional genes of this class by characterizing chromosomal sequences that are adjacent to common sites of retroviral integration in tumors.