A3 adenosine receptor activation inhibits cell proliferation via phosphatidylinositol 3-kinase/Akt-dependent inhibition of the extracellular signal-regulated kinase 1/2 phosphorylation in A375 human melanoma cells

Adenosine exerts its effects through four subtypes of G-protein-coupled receptors: A(1), A(2A), A(2B), and A(3). Stimulation of the human A(3) receptor has been suggested to influence cell death and proliferation. The phosphatidylinositide-3-OH kinase (PI3K)/Akt and the Raf/mitogen-activated protein kinase (MAPK/ERK) kinase (MEK)/mitogen-activated protein kinase (MAPK) pathways have central roles in the regulation of cell survival and proliferation. Due to their importance, the cross-talk between these two pathways has been investigated. Here, we show that the A(3) adenosine receptor agonist Cl-IB-MECA stimulates PI3K-dependent phosphorylation of Akt leading to the reduction of basal levels of ERK1/2 phosphorylation, which in turn inhibits cell proliferation. The response to Cl-IB-MECA was not blocked by A(1), A(2A), or A(2B) receptor antagonists, although it was abolished by A(3) receptor antagonists. Furthermore, the response to Cl-IB-MECA was generated at the cell surface, since the inhibition of A(3) receptor expression, by using small interfering RNA, abolished agonist effects. Using A375 cells, we show that A(3) adenosine receptor stimulation results in PI3K-dependent phosphorylation of Akt, leading to the reduction of basal levels of ERK1/2 phosphorylation, which in turn inhibits cell proliferation.