505.7 - Unconventional GPCR-PKA Signaling in the Hedgehog Pathway

Benjamin Myers (University of Utah School of Medicine), John Happ (University of Utah School of Medicine), Corvin Arveseth (University of Utah School of Medicine), Jessica Bruystens (University of California), Daniela Bertinetti (University of Kassel), Isaac Nelson (University of Utah School of Medicine), Cristina Olivieri (University of Minnesota), Danielle Hedeen (University of Utah School of Medicine), Ju-Fen Zhu (University of Utah School of Medicine), Jacob Capener (University of Utah School of Medicine), Jan Broeckel (University of Kassel), Lily Vu (University of California), C. C. King (University of California), Victor Ruiz-Perez (Universidad Autonoma de Madrid), Gianluigi Veglia (University of Minnesota), Friedrich Herberg (University of Kassel), Susan Taylor (University of California)

The Hedgehog pathway controls tissue and organ development throughout animal evolution and drives several widespread skin and brain cancers. A pivotal step in Hh signal transduction is the activation of GLI transcription factors by the atypical G protein-coupled receptor (GPCR) Smoothened (SMO). How SMO activates GLI has remained unclear for decades. The principal issue is that SMO appears to defy standard signaling paradigms utilized by nearly all other GPCRs.

Here we show that SMO employs a decoy substrate sequence to physically block the active site of the PKA catalytic subunit (PKA-C) and extinguish its enzymatic activity. As a result, GLI is released from phosphorylation-induced inhibition. Using a combination of in vitro, cellular, and organismal models, we demonstrate that interfering with SMO / PKA pseudosubstrate interactions prevents Hh signal transduction. The mechanism we uncovered echoes one utilized by the Wnt cascade, revealing an unexpected similarity in how these two essential developmental and cancer pathways signal intracellularly.  

Our findings help to resolve a longstanding mystery in developmental and cancer signaling, and reveal a new mechanism of receptor-kinase communication that may apply broadly throughout the GPCR superfamily. Our work also suggests new mechanism-inspired therapeutic strategies to manage cancers driven by ectopic Hedgehog pathway activity.

Support or Funding Information

Benjamin Myers acknowledges support from the 5 for the Fight Foundation and a Cancer Center Support Grant Pilot Project Fund from the Huntsman Cancer Institute. This work was supported by the funding line Future (PhosMOrg) of University of Kassel (Friedrich Herberg), and NIH grants R01GM100310-08 (Gianluigi Veglia), 1R35GM130389 (Susan Taylor), 1R03TR002947 (Susan Taylor) and 1R35GM133672 (Benjamin Myers).