Abstract
We examined the effects of histamine and its agonists on the expression of the c-fos and c-myc proto-oncogenes at the transcriptional and translational levels in the human promonocytic U937 cell line. Histamine transiently increased cAMP and c-fos expression through H2 receptors. Dibutyryl cAMP also increased c-fos mRNA and protein, and levels remained elevated even after 12 hr of treatment. Dose-dependence studies using histamine and dimaprit showed that the EC50values for cAMP production and c-fos increase were similar, suggesting that cAMP might be involved in c-fosinduction via H2 receptors. Furthermore, studies carried out using H7, a protein kinase A/protein kinase C inhibitor, blocked c-fos induction, whereas no effect was observed with bisindolylmaleimide, a specific protein kinase C inhibitor. No modification of c-myc expression could be detected on treatment with histamine or its analogues. Nevertheless, dibutyryl cAMP induced a down-regulation of the levels of this proto-oncogene. In addition, dibutyryl cAMP inhibited cell growth in a dose-dependent manner, whereas histamine failed to affect proliferation and differentiation of U937 cells. Cells pretreated with dimaprit showed a decrease in the cAMP response to subsequent addition of H2agonists, whereas the cAMP response to prostaglandin E2remained unaltered. This homologous mechanism of H2receptor desensitization was time dependent. These results indicate that histamine activates several mechanisms involved in the induction of differentiation, such as cAMP and c-fos production, but fails to promote differentiation of U937 cells, apparently due to the rapid desensitization of H2 receptors.
Footnotes
- Received January 7, 1997.
- Accepted February 14, 1997.
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Send reprint requests to: Dr. Alberto Baldi, Institute of Biology and Experimental Medicine, Obligado 2490 (1428), Buenos Aires, Argentina. E-mail: abaldi{at}proteus.dna.uba.ar
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This work was supported in part by grants from the University of Buenos Aires (FA005), Antorchas Foundation, and National Research Council of Argentina (CONICET).
- The American Society for Pharmacology and Experimental Therapeutics
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