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Rap1 is a small, Ras-like GTPase that was first identified as a protein that could suppress the oncogenic transformation of cells by Ras. Rap1 is activated by several extracellular stimuli and may be involved in cellular processes such as cell proliferation, cell differentiation, T-cell anergy and platelet activation. At least three different second messengers, namely diacylglycerol, calcium and cyclic AMP, are able to activate Rap1 by promoting its release of the guanine nucleotide GDP and its binding to GTP. Here we report that activation of Rap1 by forskolin and cAMP occurs independently of protein kinase A (also known as cAMP-activated protein kinase). We have cloned the gene encoding a guanine-nucleotide-exchange factor (GEF) which we have named Epac (exchange protein directly activated by cAMP). This protein contains a cAMP-binding site and a domain that is homologous to domains of known GEFs for Ras and Rap1. Epac binds cAMP in vitro and exhibits in vivo and in vitro GEF activity towards Rap1. cAMP strongly induces the GEF activity of Epac towards Rap1 both in vivo and in vitro. We conclude that Epac is a GEF for Rap1 that is regulated directly by cAMP and that Epac is a new target protein for cAMP.

Original publication

DOI

10.1038/24884

Type

Journal article

Journal

Nature

Publication Date

03/12/1998

Volume

396

Pages

474 - 477

Keywords

3T3 Cells, Amino Acid Sequence, Animals, CHO Cells, Cell Line, Cloning, Molecular, Colforsin, Cricetinae, Cyclic AMP, Cyclic AMP-Dependent Protein Kinases, GTP-Binding Proteins, Guanine Nucleotide Exchange Factors, Humans, Mice, Molecular Sequence Data, Proteins, Rats, Signal Transduction, rap GTP-Binding Proteins, ras Guanine Nucleotide Exchange Factors