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Targets of the oncogenic transcription factor v-Jun in the murine cell line C3H 10T1/2 cells have been identified using DNA microarrays. Two targets, Akap12 and Marcks, are downregulated in transformed cells and are known tumor suppressor genes. Overexpression of either Akap12 or Marcks in v-Jun-transformed cells reverses the transformed phenotype and leads to the re-expression of the other tumor suppressor gene, suggesting that these two genes cooperate in the establishment of the nontransformed state. Reverted cells continue to express v-Jun at high levels and also re-express c-Jun, which is normally repressed by v-Jun. A panel of six cell lines has been generated to evaluate the expression levels of other v-Jun targets in 10T1/2 cells. With these cells, we find that the upregulated target Sprr1a has an expression pattern that correlates with the transformed phenotype., (Copyright 2004 Nature Publishing Group)

DF-1 is a continuous cell line of chicken embryo fibroblasts. The cells are free of endogenous sequences related to avian sarcoma and leukosis viruses and have normal fibroblastic morphology. DF-1 cells support the replication of avian retroviruses; diverse oncogenes induce foci of oncogenic transformation on monolayers of DF-1, and avian leukosis viruses of envelope subgroups B, D, and C induce cell death and form plaques. The new cell line will greatly facilitate studies on oncogenic transformation and cell killing by avian viruses., (Copyright 1998 Academic Press.)

The v-jun oncogene encodes a nuclear DNA binding protein that functions as a transcription factor and is part of the activator protein 1 complex. Oncogenic transformation by v-jun is thought to be mediated by the aberrant expression of specific target genes. To identify such Jun-regulated genes and to explore the mechanisms by which Jun affects their expression, we have fused the full-length v-Jun and an amino-terminally truncated form of v-Jun to the hormone-binding domain of the human estrogen receptor. The two chimeric proteins function as ligand-inducible transactivators. Expression of the fusion proteins in chicken embryo fibroblasts causes estrogen-dependent transformation.

The retroviral oncogene qin codes for a protein that belongs to the family of the winged helix transcription factors. The viral Qin protein, v-Qin, differs from its cellular counterpart, c-Qin, by functioning as a stronger transcriptional repressor and a more efficient inducer of tumors. This observation suggests that repression may be important in tumorigenesis. To test this possibility, chimeric proteins were constructed in which the Qin DNA-binding domain was fused to either a strong repressor domain (derived from the Drosophila Engrailed protein) or a strong activator domain (from the herpes simplex virus VP16 protein). The chimeric transcriptional repressor, Qin-Engrailed, transformed chicken embryo fibroblasts in culture and induced sarcomas in young chickens. The chimeric activator, Qin-VP16, failed to transform cells in vitro or in vivo and caused cellular resistance to oncogenic transformation by Qin. These data support the conclusion that the Qin protein induces oncogenic transformation by repressing the transcription of genes which function as negative growth regulators or tumor suppressors.

The four nuclear factor I genes (NFI-A, NFI-B, NFI-C, and NFI-X) give rise to multiple isoforms by alternative splicing in many tissues. These NFI proteins cooperate with AP-1, Myc, and other transcription factors in regulating transcription of numerous cellular and viral genes. We have investigated the growth-regulatory potential of NFI by overexpressing cDNAs from chicken NFI genes -A, -B, -C, and -X in chicken embryo fibroblasts (CEF). None of the NFI cDNAs induced oncogenic transformation of CEF. However, overexpression of each of the NFI proteins caused similar morphological alteration of the cells, inducing them to become flattened and polygonal and to show increased adherence. The growth properties of these cells were similar to normal CEF. When these morphologically altered CEF were challenged by superinfection with oncogenic retroviruses, they were resistant to transformation by the nuclear oncogenes jun, fos, junD, myc, and qin but were readily transformed by cytoplasmic oncogenes src, mil/raf, ras, and fps. The NFI-A1 protein was able to alter transactivation by the cellular and viral Jun proteins in a promoter-dependent manner. The changes in cell morphology and reduced susceptibility to nuclear oncogenes were not seen with a carboxy-terminal truncation in the transactivation domain of NFI, suggesting that this region of the protein is essential for the observed effects. The dichotomy between the activities of nuclear and of cytoplasmic oncogenes in this system is discussed.