Transforming growth factor-beta relieves stem cell factor-induced proliferation of myelogenous leukemia cells through inhibition of binding of the transcription factor NF-jun.
Transforming growth factor-beta (TGF-beta) is a potent inhibitor of growth factor-stimulated hematopoiesis in normal and leukemic conditions. Using the factor-dependent myelogenous leukemia cell lines GF-D8 and Mo7, we show that TGF-beta interferes with stem cell factor (SCF)-induced proliferation by downmodulating c-jun gene expression. The ability of SCF to induce accumulation of c-jun transcripts was abolished when TGF-beta was present in culture. Transcriptional nuclear run-on assays indicated that TGF-beta relieved the capacity of SCF to enhance the transcriptional rate of the c-jun gene. Deletion analysis of the c-jun promoter furthermore showed that SCF was activating the c-jun promoter via the NF-jun transcription factor. Gel mobility shift assays showed that SCF increased the binding activity of NF-jun to its recognition site within 5 to 15 minutes. Binding activity peaked at 1 hour after exposure to SCF and declined to starting levels within 4 hours. The ability of SCF to enhance NF-jun binding activity was also dose-dependent in the range of 5 to 100 ng/mL. Exposure of GF-D8 and Mo7 cells to TGF-beta before the addition of SCF antagonized SCF-induced NF-jun binding. Moreover, whereas SCF was capable of functionally activating a heterologous promoter containing the NF-jun binding site, pretreatment of GF-D8 cells with TGF-beta abolished transcriptional activation of this heterologous promoter. These findings indicate that SCF-mediated activation of c-jun via NF-jun is crucial for the SCF-inducible proliferative response and is inhibited by TGF-beta. In additional experiments, the antisense technique was used. Treatment of GF-D8 and Mo7 cells with an antisense oligodeoxyribonucleotide directed against the translation initiation site of c-jun abolished the capacity of SCF to induce a proliferative response, whereas sense and nonsense oligomers had no effect. Taken together, our data indicate that the counteracting modulation of the binding activity of NF-jun by SCF and TGF-beta regulates the expression of the c-jun gene and thereby the proliferative state of the GF-D8 and Mo7 target.
Sott
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Department of Medical Oncology and Applied Molecular Biology, Freie Universität Berlin, Universitätsklinikum Rudolf Virchow, Germany.
Dorner
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B
Karawajew
L
L
Herrmann
F
F
Brach
M A
MA
D001665:Binding Sites; D002455:Cell Division; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D015870:Gene Expression; D016758:Genes, jun; D016298:Hematopoietic Cell Growth Factors / Q000494:pharmacology*; D006801:Humans; D007951:Leukemia, Myeloid / Q000378:metabolism / Q000473:pathology*; D009687:Nuclear Proteins / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000737:chemistry / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D011994:Recombinant Proteins; D019089:Stem Cell Factor; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D016298:Hematopoietic Cell Growth Factors; D009687:Nuclear Proteins; D016376:Oligonucleotides, Antisense; D016755:Proto-Oncogene Proteins c-jun; D011994:Recombinant Proteins; D019089:Stem Cell Factor; D016212:Transforming Growth Factor beta; C074084:nuclear factor-jun; D004247:DNA