Major histocompatibility class II transactivator expression in smooth muscle cells from A2b adenosine receptor knock-out mice -: Cross-talk between the adenosine and interferon-γ signaling

Atherosclerosis characterized by sustained inflammation and aberrant extracellular matrix alterations. Our previous investigation has defined major histocompatibility class II transactivator ( CIITA) as a key factor in mediating these two processes in smooth muscle cells. Here, we demonstrate that CIITA and major histocompatibility class II expression are elevated in interferon-gamma (IFN-gamma)-treated smooth muscle cells from A2b adenosine receptor ( A2bAR(-/-)) knock- out mice, as compared with wild type cells. An A2-type adenosine receptor agonist suppresses these effects of IFN-gamma in wild type cells, which can be blocked by an A2bAR-specific antagonist. We further identify that increased cellular cAMP levels are responsible for the down-regulation of CIITA expression and, hence, reduced IFN-gamma response as evidenced by the following data: 1) direct activation of adenylyl cyclase activity is both necessary and sufficient to suppress the IFN-gamma response; 2) inhibition of phosphodiesterase activity attenuates IFN-gamma induced transcription events; and 3) direct treatment with cAMP analog abrogates CIITA activation and IFN-gamma response. Therefore, our data establish possible crosstalk between the adenosine signaling through cAMP and IFN-gamma during regulation of CIITA expression.