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Cyclic AMP mimics IL-1 action in augmenting the differentiation of a mouse myeloid leukemic cell line (M1)
1From the Department of Hygienic Chemistry, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan.
Abstract:
We have shown previously that recombinant human interleukin 1(IL-1) and interleukin 6 (IL-6) inhibited the proliferation of a mouse myeloid leukemic cell line (M1), and that IL-6 induced differentiation of the cells into macrophage-like cells and that IL-1 augmented this differentiation. Using this model we investigated the action mechanisms of IL-1 and IL-6. IL-6, but not IL-1, stimulated prostaglandin E2 (PGE2) production. The differentiative effect of IL-6 however, was not suppressed by indomethacin, although PGE2 induction by IL-6 was completely inhibited. Exogenously added PGE2 neither augmented the differentiative effect of IL-6 nor induced differentiation in combination with IL-1. Therefore, stimulation of PGE2 production did not appear to be essential for differentiative effects of these cytokines. Dibutyryl cAMP, 8-Br-cAMP and two adenylate cyclase-activating reagents, cholera toxin (CT) and forskolin (FK), all exhibited the similar augmenting effects as IL-1. These reagents augmented M1 cell differentiation by IL-6, and they did not induce differentiation in combination with IL-1. cAMP derivatives, CT, FK, IL-1 and IL-6 all inhibited the proliferation of M1 cells. CT and FK increased the intracellular cAMP levels. However, neither IL-1 nor IL-6 increased the cAMP levels. In contrast to the cAMP derivatives and reagents that activate adenylate cyclase activity, phorbol 12-myristate 13-acetate (PMA) and calcium ionophore neither induced nor augmented the differentiation in combination with either IL-1 or IL-6. Intracellular Ca2+ concentration was not altered by IL-1 or IL-6 suggesting that Ca2+/Calmodulin kinase and protein kinase C activation are not involved in this signal transduction pathway. Therefore, the present study suggests that IL-1 exhibits an effect similar to that of cAMP without affecting intracellular cAMP level.
Insights
Interleukin-1 (IL-1) and Interleukin-6 (IL-6) inhibit myeloid leukemic cell proliferation. IL-1 mimics cyclic AMP (cAMP) effects without increasing intracellular cAMP levels, suggesting a novel signaling pathway.
Area of Science:
- Cell Biology
- Immunology
- Molecular Signaling
Background:
- Recombinant human interleukin-1 (IL-1) and interleukin-6 (IL-6) are known to inhibit myeloid leukemic cell line (M1) proliferation.
- IL-6 induces macrophage-like differentiation, while IL-1 augments this process in M1 cells.
Purpose of the Study:
- To investigate the action mechanisms of IL-1 and IL-6 in M1 cell proliferation and differentiation.
- To elucidate the signaling pathways involved in the effects of IL-1 and IL-6 on M1 cells.
Main Methods:
- Treatment of M1 cells with IL-1, IL-6, prostaglandin E2 (PGE2), dibutyryl cAMP, 8-Br-cAMP, cholera toxin (CT), forskolin (FK), phorbol 12-myristate 13-acetate (PMA), and calcium ionophore.
- Assessment of cell proliferation, differentiation, prostaglandin E2 production, intracellular cAMP levels, and intracellular Ca2+ concentration.
Main Results:
- IL-6 stimulated PGE2 production, but this was not essential for IL-6-induced differentiation.
- IL-1's augmenting effect on IL-6-induced differentiation was mimicked by cAMP analogs and adenylate cyclase activators (CT, FK), but not by PMA or calcium ionophore.
- IL-1 and IL-6 inhibited M1 cell proliferation without altering intracellular cAMP or Ca2+ levels, suggesting distinct signaling pathways from cAMP or Ca2+/PKC activation.
Conclusions:
- Prostaglandin E2 production is not essential for the differentiation effects of IL-1 and IL-6.
- IL-1 exhibits effects similar to cAMP without increasing intracellular cAMP levels, indicating a novel signaling mechanism.
- The signaling pathways for IL-1 and IL-6 do not involve protein kinase C or altered intracellular calcium concentrations.