Mature murine B lymphocytes immortalized by Kirsten sarcoma virus

Interleukin-3 withdrawal induces an early increase in mitochondrial membrane potential unrelated to the Bcl-2 family. Roles of intracellular pH, ADP transport, and F(0)F(1)-ATPase

Cytokines such as interleukin-3 (IL-3) promote the survival of hematopoietic cells through mechanisms that are not well characterized. Withdrawal of IL-3 from an IL-3-dependent pro-B cell line induced early stress-related events that preceded cell death by more than 40 h. Intracellular pH rose above pH 7.8, peaking 2-3 h post-IL-3 withdrawal, and induced a transient increase in mitochondrial membrane potential (Delta Psi(m)) detected using several different dyes. Similar events were observed following IL-7 withdrawal from a different dependent cell line. Bcl-2, Bax, and caspases were unrelated to these early events. Intracellular alkaline pH inhibited the mitochondrial import of ADP, which would limit ATP synthesis. Total cellular ATP sharply declined during this early period, presumably as a consequence of suppressed ADP import. This was followed by an increase in reduced pyridine nucleotides. The transient increase in Delta Psi(m) was blocked by oligomycin, an inhibitor of F(0)F(1-)ATPase that may have undergone reversal caused by the abnormal ADP-ATP balance within mitochondria. These findings suggest a novel sequence of early events following trophic factor withdrawal in which alkaline pH inhibits ADP import into mitochondria, reversing the F(0)F(1-)ATPase, which in turn consumes ATP and pumps out protons, raising Delta Psi(m).

Development of new cell lines for animal cell biotechnology

Mammalian cell culture has been an important technique in laboratory-scale experimentation for many decades. Developments in large-scale culture have been due to the need to grow large numbers of cells to support the growth of viruses for vaccine production, and more recently, for growing hybridoma cells as a source of monoclonal antibody. Increasingly, however, pharmaceutical products such as hormones, enzymes, growth factors, and clotting factors are being produced from cell lines which have been manipulated by recombinant DNA techniques. It is clear, therefore, that the high cost of growing mammalian cells on a large scale does not necessarily prohibit their use for biotechnology, and indeed there is considerable evidence to suggest that animal cell biotechnology will continue to be a major growth area in the future.

A v-H-ras-dependent hemopoietic tumor model involving progression from a clonal stage of transformation competence to autocrine interleukin 3 production

Autocrine interleukin 3 (IL-3)-secreting tumors were generated from an IL-3-dependent mouse mast cell line (PB-3c) after introduction of the v-H-ras oncogene. Tumor progression was characterized by four distinct phenotypes. The first corresponded to immortalized mast cells unresponsive to the oncogenic effect of v-H-ras. The second was expressed in a clonable subpopulation of PB-3c cells and was marked by the competence to form v-H-ras-dependent tumors (immortalized transformation competence). The third was a direct effect of v-H-ras expression on all PB-3c cells and was characterized in vitro by a reduced IL-3 requirement. Upon injection of v-H-ras-expressing, transformation-competent cells into mice, the final, fully malignant phenotype developed with a long latency period and was marked in vitro by independence of exogenous IL-3 and by autocrine IL-3 stimulation. Northern (RNA) blot analysis and an RNase A-T1 protection assay showed that IL-3 production was strictly associated with the tumor phenotype. Two of six tumors showed an alteration at the 5' region of the IL-3 gene. We conclude that v-H-ras required complementation by IL-3 gene rearrangement or an alternate event to generate autocrine mastocytomas.

A v-H-ras-dependent hemopoietic tumor model involving progression from a clonal stage of transformation competence to autocrine interleukin 3 production

Autocrine interleukin 3 (IL-3)-secreting tumors were generated from an IL-3-dependent mouse mast cell line (PB-3c) after introduction of the v-H-ras oncogene. Tumor progression was characterized by four distinct phenotypes. The first corresponded to immortalized mast cells unresponsive to the oncogenic effect of v-H-ras. The second was expressed in a clonable subpopulation of PB-3c cells and was marked by the competence to form v-H-ras-dependent tumors (immortalized transformation competence). The third was a direct effect of v-H-ras expression on all PB-3c cells and was characterized in vitro by a reduced IL-3 requirement. Upon injection of v-H-ras-expressing, transformation-competent cells into mice, the final, fully malignant phenotype developed with a long latency period and was marked in vitro by independence of exogenous IL-3 and by autocrine IL-3 stimulation. Northern (RNA) blot analysis and an RNase A-T1 protection assay showed that IL-3 production was strictly associated with the tumor phenotype. Two of six tumors showed an alteration at the 5' region of the IL-3 gene. We conclude that v-H-ras required complementation by IL-3 gene rearrangement or an alternate event to generate autocrine mastocytomas.

Human T-cell leukemia virus type I infection of CD4+ or CD8+ cytotoxic T-cell clones results in immortalization with retention of antigen specificity

The human T-cell leukemia virus type I (HTLV-I) is capable of chronically infecting various types of T cells and nonlymphoid cells. The effects of chronic infection on the specific functional activities and growth requirements of mature cytotoxic T lymphocytes (CTL) have remained poorly defined. We have, therefore, investigated the results of HTLV-I infection of both CD4+ and CD8+ human CTL clones. HTLV-I infection resulted in the establishment of functional CTL lines which propagated indefinitely in culture many months longer than the uninfected parental clone. The infected cells became independent of the need for antigen (target cell) stimulation as a requirement for proliferation and growth. Like their uninfected counterparts, however, these HTLV-I-infected clones remained strictly dependent on conditioned medium from mitogen-stimulated T lymphocytes for their growth. This growth factor requirement was not fulfilled by recombinant interleukin-2 alone. Furthermore, the infected lines remained functionally identical to their uninfected parental CTL clones in their ability to specifically recognize and lyse the appropriate target cells. Our findings indicate that the major effects of HTLV-I infection on mature CTL consist of (i) the capacity for proliferation in the absence of antigen stimulation and (ii) a prolonged or immortal survival in vitro, but they also indicate that the fine specificity and cytolytic capacity of these cells remain unaffected.

Immortalization of human endothelial cells by murine sarcoma viruses, without morphologic transformation

Amphotropic murine leukemia virus pseudotypes of murine sarcoma viruses containing the ras or mos oncogenes were constructed to permit efficient introduction of the sarcoma virus genome into early-passage human umbilical vein endothelial cells. The resulting cell lines were morphologically and phenotypically unchanged, retaining properties characteristic of differentiated endothelial cells. For example, the cells in a Kirsten sarcoma virus-modified line were found to biosynthesize and secrete von Willebrand factor in both a constitutive and regulated manner, and they contained ultrastructurally identifiable Weibel-Palade bodies, an endothelial cell-specific organelle. In contrast to the parent cultures, sarcoma virus-modified cells were able to proliferate indefinitely in culture. Examination of both Kirsten sarcoma and Moloney leukemia virus-modified lines indicated that the immortalized cells retained a diploid female karyotype after over 18 months in culture. In addition, the sarcoma virus-modified cells were able to grow independently of added endothelial cell growth factor. This growth factor autonomy does not appear to be due to autocrine production of a biologically cross-reactive growth factor. These immortal, virus-modified endothelial cells express large amounts of sarcoma virus-specific mRNA but no detectable helper virus or transforming virus activity. This technique for immortalization of primary human cells without alteration of the differentiated characteristics of the cell type is readily applied to a variety of human cell types. Moreover, the ability to separate the immortalizing and transforming activities of viral oncogenes should provide further understanding as to mechanisms of oncogene action.

Immortalization of human lymphocytes by transfection with DNA from mouse L929 cytoplasts

Transfection of human peripheral blood lymphocytes with DNA from mouse L929 cytoplasts induced proliferation of lymphocytes and the formation of B and T cell-derived cell lines with apparently unlimited growth potential. The cell lines could be grown in serum-containing media as well as in chemically defined serum-free media, have a nearly normal human karyotype, did not form colonies in soft-agar medium, and were not tumorigenic after injection into nude mice. For immortalization of human lymphocytes, DNA from L929 cytoplasts was 100-fold more efficient than L929 nuclear DNA. The ability of cytoplast DNA to immortalize lymphocytes could be consecutively transferred by using total cellular DNA from primary or secondary transfectants. Circular or linear mitochondrial DNA of L929 cells did not lead to immortalization of human lymphocytes. Since DNA with immortalizing activity could be isolated from cytoplasts, the Hirt supernatant, and a mitochondria-depleted cytoplasmic fraction of L929 cells, we conclude that the immortalizing DNA is located extramitochondrially in the cytoplasm of L929 cells.