Two pathways of signal transduction are activated in the same cell by different cytokines

Interleukin-3 and interleukin-6 stimulate bovine adrenal cortisol secretion through different pathways

Several interleukins have been reported to play a major role in the regulation of steroid secretion at all three levels of the hypothalamic-pituitary-adrenal axis. The objective of this study was to investigate the effect of interleukin-3 (IL-3) and interleukin-6 (IL-6) on cortisol secretion of bovine adrenocortical cells in primary culture under serum-free conditions. Both IL-3 and IL-6 stimulated basal cortisol secretion dose-dependently to a similar extent at a similar time course. After incubation with IL-3 or IL-6 at concentrations of 100 microg/l, a maximum 4.1-fold increase of the cortisol secretion was reached after 12 h (P<0.01). Coincubation of IL-3 and IL-6 (100 microg/l) revealed no significant synergism. To elucidate a possible involvement of arachidonic acid metabolites in the signal transduction, we coincubated IL-3 or IL-6 together with the cyclo-oxygenase inhibitor indometacin or the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA). Coincubation with indometacin completely abolished the stimulatory effect of IL-6 but had no effect on IL-3 stimulated cortisol secretion. In contrast, specific inhibition of the lipoxygenase system by nordihydroguaiaretic acid blocked IL-3 stimulated steroidogenesis while the effect of IL-6 was not affected. Neither IL-3 nor IL-6 altered cAMP levels significantly, whereas ACTH significantly induced cAMP levels in parallel to its steroidogenic effect. In conclusion, our data indicate that IL-3 and IL-6 stimulate the steroid secretion of bovine adrenocortical cells to a similar extent and with a similar time course. However, the effects of IL-3 and IL-6 are mediated through different, cAMP-independent pathways. While the stimulatory effect of IL-3 seems to be dependent on the lipoxygenase pathway, the effect of IL-6 on adrenocortical cortisol secretion is mediated through the cyclo-oxygenase pathway.

Aurintricarboxylic acid inhibits apoptosis and supports proliferation in a haemopoietic growth-factor dependent myeloid cell line

The actions of the nuclease inhibitor aurintricarboxylic acid (ATA) were investigated in the growth-factor dependent murine myeloid cell line NSF-60. NSF-60 cells proliferate in response to interleukin-3 (IL-3) and undergo apoptosis when deprived of exogenous IL-3, as demonstrated by the appearance of characteristic DNA 'ladders' following agarose gel electrophoresis. ATA, at concentrations between 5 and 25 microM, inhibited apoptosis in growth-factor deprived cells as demonstrated by inhibition of DNA fragmentation and increased cell survival. ATA at a concentration of 25 microM supported proliferation of the cell line in the absence of exogenous growth-factor. Both ATA and IL-3 increased protein phosphorylation in this cell line. ATA and IL-3 induced proliferation was inhibited by the kinase inhibitors genistein, staurosporine and H-7. These findings suggest that, in NSF-60, ATA is not acting exclusively as an endonuclease inhibitor and that protein phosphorylation is involved in the mechanism of action of ATA in this cell line.