Inhibition of Gα(s)/cAMP Signaling Decreases TCR-Stimulated IL-2 transcription in CD4(+) T Helper Cells

Background: The role of cAMP in regulating T cell activation and function has been controversial. cAMP is generally known as an immunosuppressant, but it is also required for generating optimal immune responses. As the effect of cAMP is likely to depend on its cellular context, the current study investigated whether the mechanism of activation of Gα(s) and adenylyl cyclase influences their effect on T cell receptor (TCR)-stimulated interleukin-2 (IL-2) mRNA levels. Methods: The effect of blocking G(s)-coupled receptor (G(s)PCR)-mediated G(s) activation on TCR-stimulated IL-2 mRNA levels in CD4(+) T cells was compared with that of knocking down Gα(s) expression or inhibiting adenylyl cyclase activity. The effect of knocking down Gα(s) expression on TCR-stimulated cAMP accumulation was compared with that of blocking G(s)PCR signaling. Results: ZM-241385, an antagonist to the G(s)-coupled A(2A) adenosine receptor (A(2A)R), enhanced TCR-stimulated IL-2 mRNA levels in primary human CD4(+) T helper cells and in Jurkat T cells. A dominant negative Gα(s) construct, Gα(s)DN3, also enhanced TCR-stimulated IL-2 mRNA levels. Similar to GsPCR antagonists, Gα(s)DN3 blocked G(s)PCR-dependent activation of both Gα(s) and Gβγ. In contrast, Gα(s) siRNA and 2’,5’-dideoxyadenosine (ddA), an adenylyl cyclase inhibitor, decreased TCR-stimulated IL-2 mRNA levels. Gα(s) siRNA, but not Gα(s)DN3, decreased TCR-stimulated cAMP synthesis. Potentiation of IL-2 mRNA levels by ZM-241385 required at least two days of TCR stimulation, and addition of ddA after three days of TCR stimulation enhanced IL-2 mRNA levels. Conclusions: G(s)PCRs play an inhibitory role in the regulation of TCR-stimulated IL-2 mRNA levels whereas Gα(s) and cAMP can play a stimulatory one. Additionally, TCR-dependent activation of Gα(s) does not appear to involve G(s)PCRs. These results suggest that the context of Gα(s)/cAMP activation and the stage of T cell activation and differentiation determine the effect on TCR-stimulated IL-2 mRNA levels.