Regulation of proliferation in a murine colony-stimulating factor-dependent myeloid cell line: superinduction of c-fos by the growth inhibitor 8-Br-cyclic adenosine 3':5' monophosphate.
We have investigated the effect of 8-Br-cyclic adenosine 3':5' monophosphate (cAMP), a pharmacological activator of cAMP-dependent protein kinase, on the proliferation and the nuclear proto-oncogene induction in a murine granulocyte macrophage colony-stimulating factor (GM-CSF)-dependent myeloid cell line. Cells were growth arrested by granulocyte macrophage colony-stimulating factor and serum deprivation and were allowed to proceed in the cell cycle by addition of the lymphokine in the presence or absence of 8-Br-cAMP. 3H-thymidine incorporation assays showed that addition of 8-Br-cAMP inhibited the entry of cells into S phase and the subsequent proliferation. Northern analysis showed that 8-Br-cAMP had opposite effects on c-fos and c-myc mRNA induction. 8-Br-cAMP induced c-fos in the absence of any GM-CSF. In the presence of GM-CSF, c-fos mRNA was superinduced (30-fold induction compared to four- to fivefold by each signal alone). On the contrary, 8-Br-cAMP was not able to induce c-myc in the absence of growth factor and hardly interfered with the induction of c-myc by GM-CSF. Phorbol myristate acetate (PMA), a pharmacological activator of the lipid and CA++-dependent protein kinase C, was shown to induce nuclear proto-oncogene mRNA in the GM-CSF-dependent cell line. We investigated the effect of 8-Br-cAMP on PMA-induced c-fos and c-myc mRNA levels. When both cAMP dependent and lipid-dependent kinase systems were co-stimulated in the absence of GM-CSF, c-fos message was again superinduced (60-fold induction). On the contrary, c-myc message induction by PMA was inhibited by 80% by coactivation of cAMP-dependent protein kinase with 8-Br-cAMP. Our data indicate that an antiproliferative signal induces or even superinduces c-fos message and hardly interferes with c-myc induction, suggesting that the intracellular pathways resulting in c-fos and c-myc induction may be distinct and that two different pathways can lead to c-fos induction, with synergistic effects when both are activated.
Harel-Bellan
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Division of Cancer Treatment, National Cancer Institute, Frederick, Maryland 21701.
Farrar
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D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D003115:Colony-Stimulating Factors / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D006131:Growth Inhibitors / Q000494:pharmacology*; D006133:Growth Substances / Q000494:pharmacology*; D011519:Proto-Oncogenes / Q000187:drug effects*; D051381:Rats
D003115:Colony-Stimulating Factors; D006131:Growth Inhibitors; D006133:Growth Substances; D015124:8-Bromo Cyclic Adenosine Monophosphate; D016178:Granulocyte-Macrophage Colony-Stimulating Factor