Adenosine-stimulated adrenal steroidogenesis involves the adenosine A2A and A2B receptors and the Janus kinase 2–mitogen-activated protein kinase kinase–extracellular signal-regulated kinase signaling pathway

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 A1, A2A, A2B, and A3 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 A2 adenosine receptors, since the antagonists specific for the A2A and A2B adenosine receptors, and specific silencing the A2A 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 A2A and A2B 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 A2 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 A2A and A2B 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.