Spatiotemporal Regulation of Signaling
Our native biochemistry studies are providing new insights into the spatiotemporal regulation of signal transduction in living cells. We focus on the cAMP/PKA, Ca2+/calcineurin, PI3K/Akt/mTOR, MAPK and AMPK pathways in the context of energy metabolism, axon polarization and genesis, insulin secretion by β cells, as well as tumorigenesis.
Discovery of an oscillatory circuit in insulin-secreting β cells. An oscillatory circuit that interlinks Ca2+, cAMP and PKA to integrate multiple input signals and coordinate key signaling activities via frequency modulation, thereby regulating complex functions in a context-dependent manner.
Calcineurin signaling in MIN6 β cells. (A) A FRET-based calcineurin activity reporter (CaNAR), which consists of a calcineurin substrate sandwiched between CFP and YFP. (B) Dual imaging of Ca2+ (red) and calcineurin activity (black) revealed integrative cytosolic calcineurin activity, contrasted by an oscillatory activity pattern on the ER, in response to Ca2+ oscillations. (C) These data are consistent with a model in which free Ca2+/CaM is less abundant near the ER surface, thereby leading to weaker calcineurin activation and calcineurin activity oscillations in this compartment.
Model of nuclear PKA microdomain. In the classical model of cAMP/PKA signaling, nuclear PKA signaling is thought to result from the gradual diffusion of activated PKA from the cytosol into the nucleus. However, our work indicates that the nucleus contains a resident pool of PKA holoenzyme, whose activity is tightly regulated through the formation of an AKAP-dependent signaling microdomain that contains both PKA holoenzyme and PDEs.