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General Comment |
By searching databases for proteins with cAMP-binding sites and homology to
guanine nucleotide exchange factors (GEFs) for RAS (190020) and RAP1, followed by RT-PCR, de Rooij et al. (1998)
isolated a cDNA encoding EPAC. Sequence analysis predicted that the 881-amino acid EPAC protein has a cAMP-binding
site; a GEF homology domain; a RAS exchange motif, which may be important in GEF structure stabilization; and a DEP
(dishevelled, egl10, pleckstrin) domain, which may be involved in membrane attachment. Northern blot analysis revealed
ubiquitous expression of EPAC, with highest levels in kidney and heart. Binding analysis confirmed a direct interaction
between EPAC and cAMP. Functional analysis showed that EPAC is a GEF for RAP1A that is directly regulated by cAMP.
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Comment |
Dynamic expression of Epac and Rap1 in mouse oocytes and preimplantation embryos. Wang JC et al. (2018) Cyclic adenosine monophosphate (cAMP) is an important secondary messenger that has long been recognized to control the initiation of meiosis through the activation of protein kinase A (PKA) in mammalian oocytes. However, PKA is not the only target for cAMP. Recent studies on cAMP-dependent and PKA-independent pathways suggest that Ras-related protein-1 (Rap1) is activated through its cAMP-responsive guanine exchange factors (cAMP-GEFs), which comprises the involvement of exchange proteins directly activated by cAMP (Epac) in various cellular processes. The aim of the present study was to investigate the possible implication of a cAMP/Epac/Rap1 pathway in mouse oocytes and embryos. Reverse transcription polymerase chain reaction and immunohistochemistry assays demonstrated the expression of Epac and Rap1 in oocytes and embryos at different stages. Immunofluorescene demonstrated that Epac and Rap1 had different dynamic subcellular localizations and expression patterns in oocytes and embryos at different stages. It was therefore indicated that Epac and Rap1 may have multiple and specific functions during oocyte maturation and embryonic development.//////////////////
Signaling pathways in ascidian oocyte maturation: The roles of cAMP/Epac, intracellular calcium levels, and calmodulin kinase in regulating GVBD. Lambert CC et al. Most mature ascidian oocytes undergo germinal vesicle breakdown (GVBD) when released by the ovary into seawater. Acidic seawater blocks this, but the oocytes can be stimulated by raising the pH, increasing intracellular cAMP levels by cell permeant forms, inhibiting its breakdown or causing its synthesis. Boltenia villosa oocytes undergo GVBD in response to these drugs. The cAMP receptor protein kinase A (PKA), however, does not appear to be involved as oocytes are not affected by the kinase inhibitor H-89. Also the PKA-independent Epac agonist 8CPT-2Me-cAMP stimulates GVBD in acidic seawater. GVBD is inhibited in calcium-free seawater (CaFSW), and by 10?M concentrations of the intracellular calcium chelator BAPTA-AM. GVBD is also inhibited when the ryanodine receptors (RYR) are blocked by tetracaine or ruthenium red, but not by the IP(3) inhibitor D-609. Dimethylbenzanthracene, a protein kinase activator, bypasses this block and stimulates GVBD in BAPTA-, tetracaine-, or ruthenium red-blocked oocytes. Finally, the calmodulin kinase inhibitor KN-93 blocks GVBD at 10?M. This and preceding articles support the hypothesis that the maturation-inducing substance produced by the follicle cells in response to increased pH activates a G protein that triggers cAMP synthesis. The cAMP then activates an Epac molecule, which causes an increase in intracellular calcium from the endoplasmic reticulum RYR. The increased intracellular calcium subsequently activates calmodulin kinase, causing an increase in cdc25 phosphatase activity, activating MPF and the progression of the oocyte into meiosis. Mol. Reprod. Dev. 2011 Wiley-Liss, Inc.
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