Radixin assembles cAMP effectors Epac and PKA into a functional cAMP compartment: role in cAMP-dependent cell proliferation.

cAMP is an ubiquitous second messenger. Localized areas with high cAMP concentration, i.e. cAMP microdomains, provide an elegant mechanism to generate signaling specificity and transduction efficiency. However, the mechanisms underlying cAMP effector targeting into these compartments is still unclear. Here we report the identification of radixin as a scaffolding unit for both cAMP effectors, Epac and PKA. This complex localizes in a submembrane compartment where cAMP synthesis occurs. Compartment disruption by shRNA and dominant negative approaches negatively affects cAMP action. Inhibition can be rescued by expression of Rap1b, a substrate for both Epac1 and PKA, but only in its GTP-bound and phosphorylated state. We propose that radixin scaffolds both cAMP effectors in a functional cAMP-sensing compartment for efficient signal transduction, using Rap1 as a downstream signal integrator.