Adenosine A_2A Receptor Facilitates Calcium-Dependent Protein Secretion through the Activation of Protein Kinase A and Phosphatidylinositol-3 Kinase in PC12 Cells

Abstract

Adenosine modulates a variety of cellular functions including calcium-dependent exocytosis. Activation of adenosine A_2A receptor (A_2A-R) facilitates neurotransmitter release in some cell types, although the underlying mechanisms are not fully understood. In this study, we found that treatment of PC12 cells with the A_2A-R agonist CGS21680 promotes calcium-evoked secretion of the fusion protein between neuropeptide Y and modified yellow fluorescence protein (NPY-Venus). CGS21680 treatment of PC12 cells transiently increased the phosphorylation of p38 and JNK MAP kinases and Akt, as well as that of ATF2 and CREB, reaching maximal levels at around 10–15 min of CGS21680 treatment. Importantly, pretreatment of PC12 cells with the PI3K inhibitor LY294002, together with the protein kinase A (PKA) inhibitor KT5720, significantly inhibited CGS21680 enhancement of calcium-dependent NPY-Venus release. Moreover, expression of a dominant-negative form of Akt and the PKA inhibitory polypeptide protein kinase inhibitor (PKI) co-operatively inhibited the facilitating effect of CGS21680 on secretion of NPY-Venus. These data suggest that the PI3K-Akt and PKA pathways play a critical role in A_2A-R-mediated facilitation of calcium-dependent secretion. We also found that CGS21680 treatment promoted recruitment of the NPY-Venus-containing vesicles to the proximity of the plasma membrane at around 10–15 min of CGS21680 treatment, which may in part account for the facilitated secretion by A_2A-R activation.