Inhibition of phorbol ester-induced monocytic differentiation by dexamethasone is associated with down-regulation of c-fos and c-jun (AP-1).
Previous studies have shown that treatment of human myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with induction of monocytic differentiation and expression of the c-jun and c-fos early response genes. The present work demonstrates that the glucocorticoid dexamethasone inhibits TPA-induced increases in c-jun and c-fos mRNA levels in U-937 leukemia cells. These findings were associated with a block in appearance of the monocytic phenotype, including inhibition of TPA-induced increases in lamin A, lamin C, and vimentin transcripts. Other studies have demonstrated that TPA-induced monocytic differentiation and expression of the c-jun and c-fos genes in myeloid leukemia cells are regulated by protein kinase C (PKC). The finding that dexamethasone has no effect on TPA-induced activation of PKC suggests that this glucocorticoid inhibits signals downstream or parallel to this enzyme. Nuclear run-on assays demonstrate that: (1) induction of c-jun and c-fos expression by TPA is regulated by transcriptional mechanisms, (2) TPA-induced expression of c-jun and c-fos does not require protein synthesis, and (3) TPA-induced expression of both genes is inhibited at the transcriptional level by dexamethasone. To further define the effects of dexamethasone at the molecular level, we prepared a series of deleted c-jun promoter fragments linked to the chloramphenicol acetyltransferase (CAT) gene. Increases in CAT activity during transient expression of these constructs in TPA-treated U-937 cells could be assigned to the region (-97 to -20) of the promoter that contains the AP-1 binding site. This induction of CAT activity was sensitive to dexamethasone. These findings suggest that dexamethasone down-regulates TPA-induced transcription of the c-jun gene during monocytic differentiation by inhibiting activation of the AP-1 site.
Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
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Hass
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Brach
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Kharbanda
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Giese
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Traub
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Kufe
D000199:Actins / Q000235:genetics; D002454:Cell Differentiation; D003907:Dexamethasone / Q000494:pharmacology*; D015536:Down-Regulation; D005786:Gene Expression Regulation / Q000187:drug effects*; D016762:Genes, fos; D016758:Genes, jun; D006801:Humans; D007951:Leukemia, Myeloid; D009000:Monocytes / Q000166:cytology*; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D000199:Actins; D016755:Proto-Oncogene Proteins c-jun; D003907:Dexamethasone; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate