Adenosine‐induced IL‐6 expression in pituitary folliculostellate cells is mediated via A2b adenosine receptors coupled to PKC and p38 MAPK

Abstract

1 Activation of adenosine receptors in folliculostellate (FS) cells of the pituitary gland leads to the secretion of IL-6 and vascular endothelial growth factor (VEGF). 2 We investigated the action of adenosine A2 receptor agonists on IL-6 and VEGF secretion in two murine FS cell lines (TtT/GF and Tpit/F1), and demonstrated a rank order of potency, 5 0 -Nethylcarboxamidoadenosine (NECA)42-p-(2-carboxyethyl)phenethylamino-5 0 -N-ethylcarboxamidoadenosine4adenosine, suggesting mediation via the A2b receptor. 3 NECA-mediated IL-6 release was inhibited by the PLC inhibitor 1-[6-((17b-3-methoxyestra-1,3,5(10)-tiene-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione, the PI3 kinase inhibitor wortmannin and the PKC inhibitors bisindolylmaleimide 1 and bisindolymaleimide X1 HCl (Ro-32-0432). 4 NECA-mediated IL-6 release was attenuated (o50%) by the extracellular signal-regulated kinase MAPK inhibitor 2 0 -amino-3 0 -methoxyflavone, and completely (495%) inhibited by the p38 MAPK inhibitor 4-(4-fluorophenyl)-2-(4-methylsulphinylphenyl)-5-(4-pyridyl)1H-imidazole. 5 NECA stimulates p38 MAPK phosphorylation that is inhibited by Ro-32-0432 but not by wortmannin. 6 Dexamethasone inhibits NECA-stimulated IL-6 and VEGF secretion. 7 These findings indicate that adenosine can stimulate IL-6 secretion in FS cells via the A2b receptor coupled principally to PLC/PKC and p38 MAPK; such an action may be important in the modulation of inflammatory response processes in the pituitary gland.

Adenosine regulates thrombomodulin and endothelial protein C receptor expression in folliculostellate cells of the pituitary gland

“…Genes that have a transcription role include thioredoxin-interacting protein (Txnip), kruppellike factor 6 (Klf6) core-binding factor, runt domain, alpha subunit 2; translocated to, 2 (CBFA2T2) and NK2 transcription factor related, locus 2 (NKX2-2). A repression of growth-inhibitory genes is consistent with our previous data where we showed that adenosine acting through A2 receptors stimulated the proliferation of TtT/GF cells [16].…”

“…Those genes that are upregulated contain several members that are associated with cytokine synthesis and immune function and membrane receptor activity and those that were inactivated were associated with anti-proliferation and transcription. IL-6 mRNA expression increased at both time points, (0.5 (30-fold) and 2 h (100-fold), consistent with our previous data on secretion [16]. Three transcription factors, NR4A1, NR4A2 and BHLHB2 (basic helix loop-helix domain containing class B2; cluster 5) were also transiently switched on at the 30-min time point before falling back to basal levels at 2 h. Of particular interest was increased expression of two related genes THBD and EPCR which are usually associated with endothelial cells and blood coagulation but have also been linked with anti-inflammation and anti-apoptosis.…”

“…However, in contrast to FS cells, THBD and EPCR expression in hormonesecreting cells does not appear to be regulated by adenosine. This, however, may relate to the differential expression of adenosine receptors in the different cell types [16].…”

“…How adenosine actually influences the protein C pathway in the pituitary gland during inflammation is unknown. In this study, we have not attempted to identify the specific adenosine receptor(s) involved although previous studies indicate that the A2b subtype is highly expressed in FS cells [15,16]. The A2b receptor has been shown to play a significant role in inflammatory processes [55].…”

“…The recent demonstration of macrophage migration inhibitory factor expression and secretion in cultured FS cells [14], and its modification by glucocorticoids, supports this contention. We have previously shown that adenosine can stimulate IL-6 production in cultured FS cells, an effect mediated via the A2b adenosine receptor subclass and involving activation of p38 MAP kinase [15,16]. Adenosine exerts anti-inflammatory actions in a number of tissues [17] and is generated in high concentration under conditions of inflammation and anoxic stress [18,19].…”