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_sPCR)-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_sPCR signaling.

Results: ZM-241385, an antagonist to the G_s-coupled A_2A adenosine receptor (A_2AR), 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_sDN3, also enhanced TCR-stimulated IL-2 mRNA levels. Similar to G_sPCR antagonists, Gα_sDN3 blocked G_sPCR-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_sDN3, 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_sPCRs 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_sPCRs. 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.