Disease relevance of RAPGEF3

• The discovery of Epac ('exchange nucleotide protein directly activated by cAMP'), a novel cAMP-binding protein, which is strongly expressed in the thyroid, raised the possibility of a role for this protein in the generation of the unexplained cold thyroid follicular adenomas [1].
• In male rats, intradermal injection of an Epac activator or estrogen alone induces mechanical hyperalgesia through a PKCepsilon-dependent mechanism [2].
• In the heart, signaling events such as the onset of cardiac hypertrophy are influenced by muscle-specific mAKAP signaling complexes that target protein kinase A (PKA), the cAMP-responsive guanine-nucleotide exchange factor EPAC and cAMP-selective phosphodiesterase 4 (PDE4) [3].

Psychiatry related information on RAPGEF3

• We first became interested in EPAC when we discovered that the expression levels of both EPAC1 and EPAC2 were altered in those regions of the brain associated with Alzheimer's disease [McPhee, Breslin, Kewney, MacKenzie, Cooreman, Gibson and Hammond (2004) International Patent number WO 2004/096199 A2] [4].
• We investigated the role of the human ortholog of Epac in tobacco smoking and nicotine dependence (ND) [5].

High impact information on RAPGEF3

• Epac is a Rap1 guanine-nucleotide-exchange factor directly activated by cyclic AMP [6].
• We have cloned the gene encoding a guanine-nucleotide-exchange factor (GEF) which we have named Epac (exchange protein directly activated by cAMP) [6].
• These methods use FRET probes based upon either protein kinase A (PKA) or EPAC, cAMP-gated ion channels, or the selective activation of AKAP-anchored PKA isoforms [7].
• Cyclic nucleotides function by binding to and activating their effectors - protein kinase A, protein kinase G, cyclic-nucleotide-regulated ion channels and the guanine nucleotide-exchange factor Epac [8].
• 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 [9].

Biological context of RAPGEF3

• Communication between the regulatory and the catalytic region of the cAMP-responsive guanine nucleotide exchange factor Epac [10].
• Therefore, through rational drug design we have developed a novel cAMP analogue, 8-(4-chloro-phenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate (8CPT-2Me-cAMP), which activates Epac, but not PKA, both in vitro and in vivo [11].
• 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) [12].
• We here examine whether varying expression of EPAC accounts for the discrepant sensitivity of B-CLL and T cells to PDE4 inhibitor-induced apoptosis [13].
• Activation of Epac also counteracts thrombin-induced hyperpermeability through down-regulation of Rho GTPase activation, suggesting cross-talk between Rap and Rho GT-Pases [14].

Anatomical context of RAPGEF3

• The addition of a membrane-targeting motif to Epac1 (Epac-CAAX) relocalizes Epac1 from its normal perinuclear locale to the plasma membrane [15].
• B-CLL and peripheral blood B cells express EPAC1 transcript, whereas T-CLL, peripheral blood T cells, monocytes, and neutrophils do not [13].
• Thus, Epac/Rap activation represents a new pathway for regulating endothelial cell barrier function [14].
• This indicates that part of the actions of LC2 in enhancing EPAC1 activity may be through stabilization of microtubules [16].
• At the end of the cell cycle, Epac is observed to reassociate with the nuclear envelope and concentrate around the contractile ring [17].

Associations of RAPGEF3 with chemical compounds

• Epac-1 and -2 (exchange proteins directly activated by cyclic AMP) are guanine-nucleotide exchange factors for the GTPases Rap1 and -2 [18].
• Furthermore, mutation of the conserved VLVLE sequence at the C-terminal end of the LID into five alanine residues makes Epac constitutively active [10].
• Two principal effector proteins for cAMP are protein kinase A (PKA) and EPAC (exchange protein directly activated by cAMP), a Rap guanosine 5'-diphosphate (GDP) exchange factor [13].
• Consistent with a role of EPAC1 in controlling integrin activity, we found that cell adhesion to laminin was enhanced in LC2- and EPAC1-transfected cells stimulated with 8-CPT-2Me-cAMP [16].
• It is also reported that Epac mediates the cAMP-dependent mobilization of Ca(2+) from intracellular Ca(2+) stores [19].
• These data demonstrate that activation of Epac1 increases integrin activity and integrin-dependent homing functions of progenitor cells and enhances their in vivo therapeutic potential [20].

Physical interactions of RAPGEF3

• Exchange protein directly activated by cAMP (EPAC) interacts with the light chain (LC) 2 of MAP1A [21].
• We subsequently developed a novel, high-throughput screen based on the displacement of [3H]cAMP from the EPAC cAMP-binding site and identified small molecule hits from the Scottish Biomedical Lead Generation Library. These compounds selectively bind to the cAMP-binding sites of EPAC1 and EPAC2 and are structurally dissimilar to cAMP [4].

Regulatory relationships of RAPGEF3

• Consistent with this, an isolated Ras exchange motif domain from Epac is sufficient to activate JNK [22].

Other interactions of RAPGEF3

• In addition to the cAMP binding domains, both Epac1 and Epac2 have a DEP domain [23].
• Furthermore, we conclude that the catalytic activity of Epac1 is constrained by a direct interaction between GEF and high affinity cAMP binding domains in the absence of cAMP [23].
• In cellular models where Rap1 is activated via endogenous GEFs, the Rap1[S17A] mutant inhibits both the cAMP-Epac and EGF-C3G pathways, whereas Rap1[G15D] selectively interferes with the latter [24].
• Rap1 activation by Epac-CAAX, but not wild-type Epac, triggers its association with B-Raf [15].
• From these results, we conclude that all three members of the Epac family regulate both Rap1 and Rap2 [23].

Analytical, diagnostic and therapeutic context of RAPGEF3

• We found that deletion of the cAMP-binding domain inhibited interaction between EPAC1 and LC2 in a two-hybrid assay, but removal of the DEP domain had little effect [21].
• We applied an immunoprecipitation assay to demonstrate protein interaction between EPAC1 and LC2 in co-transfected human embryonic kidney 293 cells [21].
• To further investigate a role for EPAC in these cells, we carried out cDNA microarray analysis of cells stimulated with 8-CPT-2Me-cAMP [25].
• Immunofluorescence study also confirmed the presence of Epac (isoform I) in IMCD [26].
• Exchange protein directly activated by cAMP (Epac) has been shown to increase its expression in rat prefrontal cortex after self-administration of nicotine [5].

References