The guanine nucleotide exchange factor CNrasGEF activates ras in response to cAMP and cGMP.
Small GTPase proteins such as Ras are key regulators of cellular proliferation and are activated by guanine nucleotide exchange/releasing factors (GEFs/GRFs). Three classes of Ras GRFs have been identified to date, represented by Sos1/2, Ras-GRF1/2 and Ras-GRP. Here, we describe a novel candidate Ras activator, cyclic nucleotide rasGEF (CNrasGEF), which contains CDC25, Ras exchange motif (REM), Ras-association (RA), PDZ and cNMP (cAMP/cGMP) binding (cNMP-BD) domains, two PY motifs and a carboxy-terminal SxV sequence. CNrasGEF can activate Ras in vitro, and it binds cAMP directly via its cNMP-BD. In cells, CNrasGEF activates Ras in response to elevation of intracellular cAMP or cGMP, or treatment with their analogues 8-Br-cAMP or 8-Br-cGMP, independently of protein kinases A and G (PKA and PKG). This activation is prevented in CNrasGEF lacking its CDC25 domain or cNMP-BD. CNrasGEF can also activate the small GTPase Rap1 in cells, but this activation is constitutive and independent of cAMP. CNrasGEF is expressed mainly in the brain and is localized at the plasma membrane, a localization dependent on the presence of intact PDZ domain but not the SxV sequence. These results suggest that CNrasGEF may directly connect cAMP-generating pathways or cGMP-generating pathways to Ras.
Pham
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N
Program in Cell Biology, Department of Biochemistry, The Hospital for Sick Children, University of Toronto, Toronto, M5G 1X8, Canada.
Cheglakov
I
I
Koch
C A
CA
de Hoog
C L
CL
Moran
M F
MF
Rotin
D
D
D000818:Animals; D002461:Cell Line, Transformed; D000071877:Checkpoint Kinase 1; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins; D006801:Humans; D051381:Rats; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism; D020663:ras Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
D029721:Drosophila Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D000242:Cyclic AMP; D000071877:Checkpoint Kinase 1; C000605877:grp protein, Drosophila; D017868:Cyclic AMP-Dependent Protein Kinases; D020827:rap1 GTP-Binding Proteins; D018631:ras Proteins; D006152:Cyclic GMP