https://digitalcommons.georgefox.edu/cgi/viewcontent.cgi?article=1044&context=bio_fac

Crosstalk between cAMP and MAP kinase signaling in the regulation of cell proliferation.

Autophagy is a major clearance route for intracellular aggregate-prone proteins causing diseases such as Huntington's disease Autophagy induction with the mTOR inhibitor rapamycin accelerates clearance of these toxic substrates As rapamycin has nontrivial side effects, we screened FDA-approved drugs to identify new autophagy-inducing pathways We found that L-type Ca2+ channel antagonists, the K+ATP channel opener minoxidil, and the G(i) signaling activator clonidine induce autophagy These drugs revealed a cyclical mTOR-independent pathway regulating autophagy, in which cAMP regulates IP3 levels, influencing calpain activity, which completes the cycle by cleaving and activating G(s)alpha, which regulates cAMP levels This pathway has numerous potential points where autophagy can be induced, and we provide proof of principle for therapeutic relevance in Huntington's disease using mammalian cell, fly and zebrafish models Our data also suggest that insults that elevate intracytosolic Ca2+ (like excitotoxicity) inhibit autophagy, thus retarding clearance of aggregate-prone proteins

Novel targets for Huntington's disease in an mTOR-independent autophagy pathway

Epac proteins: multi-purpose cAMP targets.

Five years ago, Epac--a guanine nucleotide exchange factor for the Ras-like small GTPases Rap1 and Rap2--was found to be a new target of cyclic AMP, which opened up new avenues for cAMP research. Structural analysis of the cAMP-binding domains of Epac2 has identified a unifying mechanism for how cAMP activates proteins, and the design and synthesis of an Epac-specific cAMP analogue has paved the way for future discoveries.

Epac: a new cAMP target and new avenues in cAMP research

Second messenger cAMP regulates many cellular functions through its effectors, such as cAMP-dependent protein kinase (PKA) and Epac (exchange proteins directly activated by cAMP). Spatial and temporal control of cAMP signaling is crucial to differential regulation of cellular targets involved in various signaling cascades. To investigate the compartmentalized cAMP signaling, we constructed fluorescent indicators that report intracellular cAMP dynamics and Epac activation by sandwiching the full-length Epac1 between cyan and yellow mutants of GFP. Elevations of cAMP decreased FRET and increased the ratio of cyan-to-yellow emissions by 10–30% in living mammalian cells. This response can be reversed by removing cAMP-elevating agents and abolished by mutating the critical residue responsible for cAMP binding. Targeting of the reporter to the plasma membrane, where cAMP is produced in response to the activation of β-adrenergic receptor, revealed a faster cAMP response at the membrane than in the cytoplasm and mitochondria. Simultaneous imaging with targeted cAMP indicator and PKA activity reporter allowed the detection of a much delayed PKA response in the nucleus after the rapid accumulation of cAMP at the plasma membrane of the same cell, despite the immediate presence of a pool of cAMP in the nucleus. Thus, cAMP dynamics and the activation of its effectors are precisely controlled spatiotemporally in vivo.

https://www.pnas.org/content/pnas/101/47/16513.full.pdf

Fluorescent indicators of cAMP and Epac activation reveal differential dynamics of cAMP signaling within discrete subcellular compartments.

Differential Signaling of Cyclic AMP OPPOSING EFFECTS OF EXCHANGE PROTEIN DIRECTLY ACTIVATED BY CYCLIC AMP AND cAMP-DEPENDENT PROTEIN KINASE ON PROTEIN KINASE B ACTIVATION

Jingbo Qiao

Papers

Differential Signaling of Cyclic AMP OPPOSING EFFECTS OF EXCHANGE PROTEIN DIRECTLY ACTIVATED BY CYCLIC AMP AND cAMP-DEPENDENT PROTEIN KINASE ON PROTEIN KINASE B ACTIVATION

Cell cycle-dependent subcellular localization of exchange factor directly activated by cAMP.