Adenosine-stimulated adrenal steroidogenesis involves the adenosine A 2A and A 2B receptors and the Janus kinase 2–mitogen-activated protein kinase kinase–extracellular signal-regulated kinase signaling pathway

Abstract

Adenosine promotes adrenal steroidogenesis in vitro and in vivo. However, the underlying signaling mechanisms of this event and the function of the adenosine receptor subtypes in adrenal cells remain to be elucidated. Expression of A 1, A 2A, A 2B, and A 3 adenosine receptor mRNA in rat adrenal cells was shown by reverse transcription-polymerase chain reaction. Adenosine increased corticosterone production in a time- and dose-dependent manner, and this adenosine effect was mediated by the A 2 adenosine receptors, since the antagonists specific for the A 2A and A 2B adenosine receptors, and specific silencing the A 2A adenosine receptor expression with small interfering RNA significantly blocked the adenosine-induced steroidogenesis. Using pharmacological approaches, we further demonstrated that Janus kinase 2 was the downstream molecule next to the A 2A and A 2B adenosine receptors. Inhibition of Janus kinase 2 prevented the adenosine-induced steroidogenesis and phosphorylation of mitogen-activated protein kinase kinase 1/2 and extracellular signal-regulated kinase 1/2, demonstrating that Janus kinase 2 was the upstream effector of the mitogen-activated protein kinase kinase pathway. Pretreatment with A 2 adenosine receptor, Janus kinase 2, or mitogen-activated protein kinase kinase inhibitors significantly decreased the adenosine-induced phosphorylation of 3′,5′-cyclic adenosine monophosphate responsive element binding protein. In conclusion, these data show that adenosine-stimulated steroidogenesis is mediated via the A 2A and A 2B adenosine receptors, activation of which triggers the Janus kinase 2–mitogen-activated protein kinase kinase–extracellular signal-regulated kinase cascade and 3′,5′-cyclic adenosine monophosphate responsive element binding protein phosphorylation. Based on its stimulatory effect on glucocorticoid production, adenosine is a potential candidate as anti-inflammatory agent.