A missense variant of adenylate cyclase 7 (AC7), p.Asp439Glu, has been significantly associated with ulcerative colitis (UC) in genome-wide association studies. Previous work suggested that this variant is reduced in expression and exhibits impaired cyclic adenosine-3′,5′-monophosphate (cAMP) synthesis, thus skewing T-cell cytokine profiles. Here, we investigated the variant’s function measuring dynamic cAMP responses in live HEK293 cells. We show that p.Asp439Glu generates significantly reduced basal cAMP levels despite normal expression. Stimulation with sphingosine-1-phosphate (S1P) and phorbol 12-myristate 13-acetate (PMA) induced a reduced cAMP increase in cells expressing mutant AC7, indicating reduced responsiveness to G-protein-coupled receptor (GPCR) and protein kinase C (PKC) activation. Western blot analysis showed altered downstream phosphorylation of cAMP response element-binding protein (CREB) and cAMP-dependent transcription factor (ATF1) in cells expressing the variant. Higher levels of phosphorylated CREB and ATF1 were observed in cells expressing p.Asp439Glu AC7 under basal conditions while stimulation with S1P had no effect on protein phosphorylation. Our findings provide direct biochemical evidence for strongly impaired AC7 function caused by the variant p.Asp439Glu. These results may pave the way for more causally defined and genotype-specific treatment strategies in UC.
Loers et al. (Sat,) studied this question.