Cellular Compensation for Chronic Decreases in Cyclic AMP Concentration: Gαs‐Deficient Dendritic Cells as a Model and Implications for Therapeutics for Allergic Disorders

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Dendritic cells (DCs), the main antigen‐presenting cells, are involved in the induction of type II helper T cell (Th2) immune responses, but the mechanism by which this occurs is not fully elucidated. Mice that have a CD11c (DC)‐specific deletion of the gene Gnas (CD11cΔGnas), which encodes the α subunit of the heterotrimeric (αβγ) G protein Gαs, display very low basal cyclic AMP (cAMP) concentrations and an allergic phenotype; the decrease in cAMP and protein kinase A (PKA) activation biases DCs to provoke a Th2 response ex vivo and in vivo (Lee et al PNAS 112: 1529–34 [2015]). By comparing the mRNA expression of cAMP pathway components in WT and CD11cΔGnas bone marrow‐derived DCs (BMDCs), we assessed how cells compensate for a chronic decrease in cAMP/PKA signaling. Using quantitative real‐time PCR (qPCR), we found that BMDCs from CD11cΔGnas mice have >2‐fold increased expression of adenylyl cyclase (AC) 3, decreased expression of numerous cyclic nucleotide phosphodiesterase (PDE) isoforms that degrade cAMP, but no overall increase in Gαi proteins or the cAMP transporter MRP4/ABCC4. We also assessed the expression of G protein‐coupled receptors (GPCRs; assayed by qPCR‐based Taqman GPCR arrays), including those that regulate cAMP formation. A greater number and larger increase in expression occurs for GPCRs that couple to Gαi (rather than other Gα proteins) in CD11cΔGnas BMDCs compared to BMDCs from WT mice. Additionally, expression of multiple PKA subunits (Cα, RIα, RIIα, RIIβ) is decreased at least 30% in CD11cΔGnas BMDCs. A‐kinase anchor protein (AKAP)6 and AKAP9 have an increase and decrease, respectively, in those BMDCs. Together, these data indicate that DCs with lower cAMP levels have altered expression of “upstream” cAMP signaling components (GPCRs and AC3) and of “downstream” components that regulate cAMP levels (PDE isoforms) and actions (PKA subunits, AKAPs). Such changes in expression of GPCRs and post‐G protein components may reflect withdrawal of “basal”, tonic effects of cAMP, may contribute to the greater Th2 responses and allergic asthma of CD11cΔGnas mice, and may be novel therapeutic targets for allergic asthma.Support or Funding InformationSupported by NIH grants R56AI110505 and T32GM007752.