Adenosine inhibits macrophage colony-stimulating factor-dependent proliferation of macrophages through the induction of p27(kip-1) expression

Adenosine is produced during inflammation and modulates different functiona l activities in macrophagcs, In murine bone marrow-derived macrophages, ade nosine inhibits M-CSF-dependent proliferation with an IC50 of 45 mu M. Only specific agonists that can activate A(2B) adenosine receptors such as 5'-N -ethylcarboxamidoadenosine, but not those active on A(1) (N-6-(R)-phenyliso propyladenosine), A(2A) ([p-(2-carbonylethyl)phenplethylamino]-5'-N-ethylca rboxamidoadenosine), or A(3) (N-6-(3-iodobenzyl)adenosine-5'-N-methyluronam ide) receptors, induce the generation of cAMP and modulate macrophage proli feration. This suggests that adenosine regulates macrophage proliferation b y interacting with the A,, receptor and subsequently inducing the productio n of cAMP, In fact, both 8-Br-cAMP (IC50 85 mu M) and forskolin (IC50 7 mu M) inhibit macrophage proliferation. Moreover, the inhibition of adenylyl c yclase and protein kinase A blocks the inhibitory effect of adenosine and i ts analogues on macrophage proliferation. Adenosine causes an arrest of mac rophages at the G(1) phase of the cell cycle without altering the activatio n of the extracellular-regulated protein kinase pathway. The treatment of m acrophages with adenosine induces the expression of p27(kip-1), a G(1) cycl in-dependent kinase inhibitor, in a protein kinase A-dependent way, Moreove r, the involvement of p27(kip-1) in the adenosine inhibition of macrophage proliferation was confirmed using macrophages from mice with a disrupted p2 7(kip-1) gene. These results demonstrate that adenosine inhibits macrophage proliferation through a mechanism that involves binding to A,, adenosine r eceptor, the generation of cAMP, and the induction of p27(kip-1) expression .