Rap1 Activates Endosomal AC9 to Drive the Second cAMP Wave

Abstract

GsPCR signaling orchestrates cAMP production in three distinct spatial waves originating from the plasma membrane (PM), endosomes, and the nucleus. While the molecular drivers of the PM and nuclear waves are well defined, the regulation of the endosomal cAMP wave remains insufficiently understood. Here, we identify the small GTPase Rap1b as a direct activator of the endosomal adenylyl cyclase 9 (AC9), revealing a novel mechanism for intracellular cAMP synthesis. Like Gs, Rap1b-GTP interacts with the C2 domain of AC9, allosterically enhancing its catalytic activity both in vitro and in cells. Using AC9 mutations that selectively disrupt Rap1b versus Gs binding, we elucidate the role of the Rap1b-AC9 unit in mediating the endosomal cAMP wave, introducing a new layer of spatial regulation to cAMP signaling.