Abelson murine leukemia virus: effect of helper virus from regressing Friend virus on leukemia development

Proliferation and differentiation of Abelson virus-infected murine myeloid leukemia cell lines does not involve an autocrine mechanism

Culture in agar of cloned promonocytic leukemia cell lines derived from Abelson virus-infected mice produced colonies of both a compact and diffuse morphology. Diffuse colonies contained fewer cells capable of forming colonies when recultured in agar than did compact colonies. Serial subcloning of cells from diffuse, but not compact, colonies ultimately led to the complete loss of colony-forming cells, i.e., to clonal extinction. The production of both compact and diffuse agar colonies was independent of the cell density of either the static liquid culture from which cells were taken for culture in agar, or the number of cells per agar culture. Furthermore, bioassays of culture supernatants indicated the leukemia cells did not secrete hemopoietic growth factors active on normal hemopoietic cells, transforming growth factors active on adherent cell lines, or factors that influenced the growth of the leukemic cells themselves. Collectively, these data suggest neither growth-factor independent replication nor the spontaneous differentiation of Abelson virus-infected myeloid cells involves autocrine secretion of growth regulators.

Differentiation of Abelson murine leukemia virus-infected promonocytic leukemia cells

Virus-producing, tumorigenic, promonocytic leukemia cell lines were derived from Abelson murine leukemia virus-infected mice. This study shows that, of these 25 cloned lines, 22 were capable of extensive differentiation. It also shows that granulocyte-macrophage colony-stimulating activity increased the proportion of differentiating cells in 17/22 lines. Cells from agar colonies with a diffuse colony morphology had an increased expression of mature macrophage phenotypic characteristics, and a reduced proliferative capacity in vitro, compared to cells from agar colonies with a compact colony morphology. Cells from diffuse colonies also produced less Abelson virus, and were less tumorigenic in vivo than cells from compact colonies. Together, these results suggest some Abelson virus-producing leukemic cells are not blocked in their capacity to differentiate and are capable of reversing the transformed phenotype.

Malignant transformation of a growth factor-dependent myeloid cell line by Abelson virus without evidence of an autocrine mechanism

Abelson virus has been used to transform cells of a murine, factor-dependent myeloid cell line (FD). Factor-independent (FI) cell lines were derived, which expressed the viral genome and were tumorigenic in syngeneic mice. Karyotypic analysis of FI cells before and after passage in vivo indicated that the tumorigenic cells were derived from FD cells. Northern gel analysis of mRNA, bioassay of culture supernatants, and the density-independent growth of the FI cells indicated that the transformation had not induced the synthesis of the hemopoietic growth factors normally required to support the FD cells, that is, granulocyte-macrophage CSF or Multi-CSF. The FD and FI cells displayed similar numbers of cell surface receptors for Multi-CSF (IL-3) and GM-CSF. We conclude that Abelson virus transformation of this line from factor-dependence to factor-independence and tumorigenicity did not involve autocrine stimulation.

Thymocyte subsets transformed by Abelson murine leukemia virus

The infectious complex of Abelson murine leukemia virus was altered by replacing its usual helper virus, Moloney leukemia virus, with radiation leukemia virus (RadLV). After intrathymic injection of the Abelson-RadLV complex, thymomas arose rapidly, as described previously for injection of the Abelson-Moloney complex. Cell lines were derived from thymomas induced by each Abelson virus complex and were classified according to normal thymus cell phenotypes. Each virus complex induced some cell lines which were like a 0.7% subpopulation of murine thymocytes in that they failed to express the Thy-1 cell-surface antigen. These lines are thus far indistinguishable from some Abelson-derived bone marrow transformants classified as pre-B cells. However, the Abelson-Moloney complex induced some cell lines which expressed low levels of Thy-1 and which shared most markers with immature blast cells of the thymic medulla, whereas the Abelson-RadLV complex induced some lines which were clearly like thymic cortex blast cells. Thus, Abelson virus can induce thymoma cell lines of at least two, and possibly three, distinct phenotypes corresponding to normal thymocyte blast subsets, the determination of which can be influenced by helper virus sequences.

Thymocyte subsets transformed by Abelson murine leukemia virus

The infectious complex of Abelson murine leukemia virus was altered by replacing its usual helper virus, Moloney leukemia virus, with radiation leukemia virus (RadLV). After intrathymic injection of the Abelson-RadLV complex, thymomas arose rapidly, as described previously for injection of the Abelson-Moloney complex. Cell lines were derived from thymomas induced by each Abelson virus complex and were classified according to normal thymus cell phenotypes. Each virus complex induced some cell lines which were like a 0.7% subpopulation of murine thymocytes in that they failed to express the Thy-1 cell-surface antigen. These lines are thus far indistinguishable from some Abelson-derived bone marrow transformants classified as pre-B cells. However, the Abelson-Moloney complex induced some cell lines which expressed low levels of Thy-1 and which shared most markers with immature blast cells of the thymic medulla, whereas the Abelson-RadLV complex induced some lines which were clearly like thymic cortex blast cells. Thus, Abelson virus can induce thymoma cell lines of at least two, and possibly three, distinct phenotypes corresponding to normal thymocyte blast subsets, the determination of which can be influenced by helper virus sequences.