Preparing your results

Our searching services are busy right now. Your search will reload in five seconds.

X
Forgot Password

If you have forgotten your password you can enter your email here and get a temporary password sent to your email.

Identification of guanine nucleotide exchange factors (GEFs) for the Rap1 GTPase. Regulation of MR-GEF by M-Ras-GTP interaction.

http://www.ncbi.nlm.nih.gov/pubmed/10934204

Although the Ras subfamily of GTPases consists of approximately 20 members, only a limited number of guanine nucleotide exchange factors (GEFs) that couple extracellular stimuli to Ras protein activation have been identified. Furthermore, no novel downstream effectors have been identified for the M-Ras/R-Ras3 GTPase. Here we report the identification and characterization of three Ras family GEFs that are most abundantly expressed in brain. Two of these GEFs, MR-GEF (M-Ras-regulated GEF, KIAA0277) and PDZ-GEF (KIAA0313) bound specifically to nucleotide-free Rap1 and Rap1/Rap2, respectively. Both proteins functioned as Rap1 GEFs in vivo. A third GEF, GRP3 (KIAA0846), activated both Ras and Rap1 and shared significant sequence homology with the calcium- and diacylglycerol-activated GEFs, GRP1 and GRP2. Similarly to previously identified Rap GEFs, C3G and Smg GDS, each of the newly identified exchange factors promoted the activation of Elk-1 in the LNCaP prostate tumor cell line where B-Raf can couple Rap1 to the extracellular receptor-activated kinase cascade. MR-GEF and PDZ-GEF both contain a region immediately N-terminal to their catalytic domains that share sequence homology with Ras-associating or RalGDS/AF6 homology (RA) domains. By searching for in vitro interaction with Ras-GTP proteins, PDZ-GEF specifically bound to Rap1A- and Rap2B-GTP, whereas MR-GEF bound to M-Ras-GTP. C-terminally truncated MR-GEF, lacking the GEF catalytic domain, retained its ability to bind M-Ras-GTP, suggesting that the RA domain is important for this interaction. Co-immunoprecipitation studies confirmed the interaction of M-Ras-GTP with MR-GEF in vivo. In addition, a constitutively active M-Ras(71L) mutant inhibited the ability of MR-GEF to promote Rap1A activation in a dose-dependent manner. These data suggest that M-Ras may inhibit Rap1 in order to elicit its biological effects.

Pubmed ID: 10934204 RIS Download

Mesh terms: Amino Acid Sequence | Blotting, Northern | Brain | Calcium | Catalytic Domain | Cell Line | DNA, Complementary | DNA-Binding Proteins | Diglycerides | Dose-Response Relationship, Drug | Enzyme Activation | Guanine Nucleotide Exchange Factors | Humans | Molecular Sequence Data | Mutagenesis | Nerve Tissue Proteins | Plasmids | Precipitin Tests | Protein Binding | Protein Structure, Tertiary | Proto-Oncogene Proteins | Proto-Oncogene Proteins c-raf | Receptors, Cytoplasmic and Nuclear | Sequence Homology, Amino Acid | Tissue Distribution | Transcription Factors | Tumor Cells, Cultured | ets-Domain Protein Elk-1 | rap GTP-Binding Proteins | rap1 GTP-Binding Proteins | ras Guanine Nucleotide Exchange Factors

Research resources used in this publication

None found

Research tools detected in this publication

None found

Data used in this publication

None found

Associated grants

None

GO (Data, Gene Annotation)

Publication data is provided by the National Library of Medicine ® and PubMed ®. Data is retrieved from PubMed ® on a weekly schedule. For terms and conditions see the National Library of Medicine Terms and Conditions.