Phosphatases control the duration and range of cAMP/PKA microdomains.

Abstract

The spatiotemporal interplay between the second messenger cyclic AMP (cAMP) and its main effector, Protein kinase A (PKA) is crucial for the pleiotropic nature of this cascade. To maintain a high degree of specificity, the cAMP/PKA axis is organised into functional units called microdomains, precisely distributed within the cell. While the subcellular allocation of PKA is guaranteed by a family of tethers called A-Kinase-anchoring Proteins (AKAPs), the mechanisms underlying the efficient confinement of a microdomain's functional effects are not fully understood. Here we used FRET-based sensors to detect cAMP levels and PKA-dependent phosphorylation within specific subcellular compartments. We find that cellular cAMP levels may depend on different mechanisms and are responsible for the activation of local PKA enzymes. On the other hand, the dephosphorylating actions of phosphatases dictate the duration of the microdomain's effects. To test the range of action of PKA microdomains we used rigid aminoacidic nanorulers to distance our FRET sensors from their original location for 10 or 30 nm. Interestingly, we established that cAMP levels do not affect the spatial range of the microdomain while on the contrary, phosphatase activity provides a functional boundary for phosphorylated PKA targets. Finally, using the same strategy to distance phosphatases from the mitochondria we found that enzymes close to the outer mitochondrial membrane produced a fragmented phenotype that was not observed when phosphatases were moved to 30 nm from the organelle's surface. Our findings contribute to the design of a picture where two microdomain-forming events have distinct roles. Cyclic AMP elevations trigger the initial activation of subcellular PKA moieties, while the temporal and spatial extent of the PKA's actions are regulated by phosphatases.