Cilia have high cAMP levels that are inhibited by Sonic Hedgehog-regulated calcium dynamics

Significance Primary cilia are immotile organelles composed of specialized structural and signaling proteins that are essential for Hedgehog (HH) signaling. cAMP-dependent protein kinase (PKA) critically regulates HH signaling, maintaining transcriptional repression. Ciliary PKA activity is critical for HH regulation; however, the signaling steps regulating PKA activity within cilia remain unclear/unexplored. Targeted sensors were used to measure signaling molecules specifically within cilia. We found that cilia have basally high cAMP and PKA activity, controlled by phosphatidylinositol (3,4,5)-trisphosphate, not G proteins. Sonic Hedgehog stimulation reduces ciliary cAMP and PKA activity, which is dependent on Ca 2+ dynamics.