Characterization of a large genomic size Moloney murine sarcoma virus produced by a transformed rat cell line

Localization and structure of v-mos in transformed mouse fibroblasts reverted by long-term interferon treatment to nonmalignancy

We have reported previously that Moloney virus-transformed cells, when treated for over 200 passages in the presence of low concentrations of mouse interferon-alpha/beta, can be reverted to a stable nonmalignant status. The cells recover full contact inhibition and are unable to raise tumors when grafted in nude mice. In the present report, we show that whether reverted or malignant, these cells contain deleted v-mos oncogenes, which have lost 392 nucleotides. The truncated oncogenes contain a reduced and modified open reading frame but are able, however, to induce tumors when transfected in mouse 3T3 cells. As there is no difference either in the location or in the structure of this modified v-mos, whether yielded by reverted or malignant cells, we postulate that both cell lines derive from the same population and this modification does not play any role in the reversion process obtained through prolonged IFN-dependent selection. We suggest that reversion could be an epigenetic phenomenon, involving the constitutive synthesis of IFN-beta only in the reverted and not in the malignant cells. The continued persistence of such noncancerous cells could result at least partly from a balance involving the expression of v-mos, IFN-beta, and an IFN antagonist, sarcolectin. These reverted cells can undergo an unlimited number of passages, but they must be trypsinized before day 5 in confluent cultures. Thereafter, the cells stop dividing, cannot proliferate anymore, progressively show signs of apoptosis, and die.

Sequence variation of human endogenous retrovirus ERV9-related elements in an env region corresponding to an immunosuppressive peptide: transcription in normal and neoplastic cells

Evolutionarily conserved sequences corresponding to an immunosuppressive region in retroviral transmembrane proteins were amplified by the polymerase chain reaction from human genomic DNA and reverse-transcribed RNA from one glioma, three pieces of macroscopically normal brain tissue, kidney, lymphocytes, cultured embryonic lung cells, and a rhabdomyosarcoma cell line. Amplification products (125 bp) from DNA and RNA from the glioma and RNA from one normal piece of brain tissue were cloned and sequenced (45 clones). A variety of sequences similar to ERV9 (75 to 93%) were identified. Amplification products were immobilized on nylon filters and hybridized to four different synthetic oligonucleotides derived from the sequenced clones. Sequences without the stop codon seen in ERV9 in this region, possibly encoding functional immunosuppressive proteins, were present in RNA amplificates from all samples. The various cell types showed different hybridization patterns with the four probes. The open reading frame sequences were identified in genomic Southern blots, one probe detecting about 10 copies and another detecting a single copy. Northern (RNA) blots of mRNA from various normal human tissues revealed 2.5-kb (e.g., lung) and 10-kb (e.g., placenta) transcripts hybridizing to one of the probes.

Persistent expression of v-mos oncogene in transformed cells that revert to nonmalignancy after prolonged treatment with interferon

BALB/c embryonic fibroblasts productively transformed by Moloney sarcoma virus and cultivated for over 600 generations in the presence of mouse alpha/beta interferon reverted to an apparently normal phenotype and were unable to produce tumors in nude mice. Nevertheless, the presence of an integrated Moloney sarcoma virus genome in the nonmalignant Moloney sarcoma virus-transformed interferon-treated cell DNA could be shown by focus formation upon transfection and by hybridization with a v-mos probe. After digestion with various restriction endonucleases, similar hybridization patterns of v-mos sequences were obtained with DNAs from both reverted and transformed cells. However, additional integration sites and at least twice as many copies of the oncogene were found in the nonmalignant Moloney sarcoma virus-transformed interferon-treated cell DNA. Polyadenylylated RNA extracted from reverted and control cells contained two mos-specific transcripts. Interestingly, the nonmalignant Moloney sarcoma virus-transformed interferon-treated cells produced helper virus, but no detectable mos-containing virions, suggesting that a posttranscriptional block in the v-mos gene expression had occurred in these cells. It should be stressed that, after up to 100 additional passages, cells cultured in the absence of interferon maintained their nontumorigenic character in spite of the persistent transcription of the mos oncogene.

Isolation from the spleen of myeloproliferative sarcoma virus-infected mice of a myelomonocytic tumor cell line secreting hematopoietic colony stimulating factors

Clonogenic tumor cells were detected in the spleen of DBA/2 mice infected with the myeloproliferative sarcoma virus (MPSV). These cells could be isolated because of their ability to proliferate on the greater omentum of sublethally irradiated isogenic recipient mice. We have established a permanent suspension myelomonocytic cell line in vitro (TE8), from a tumor obtained after subcutaneous transplantation of the omental tumor masses. The TE8 cells are clonogenic in semi-solid medium containing agarose. The colonies thus obtained gave rise to myelomonocytic cell lines growing in suspension in liquid medium. One of those cloned cell lines, C1(1011) was studied in details. It is exclusively composed of initial donor cells, it is tumorigenic in vivo, clonogenic in vitro and produces MPSV. It also secretes a colony stimulating activity (CSA), and an activity termed mixed colony promoting activity (MPA), which enables pluripotent hematopoietic stem cells to proliferate and differentiate. It differentiates through the granulomacrophage cell line independently of exogenous factors other than those which may be present in the serum.