Cloning and characterization of GEF-H1, a microtubule-associated guanine nucleotide exchange factor for Rac and Rho GTPases.
The Rho-related small GTPases are critical elements involved in regulation of signal transduction cascades from extracellular stimuli to cell nucleus and cytoskeleton. The Dbl-like guanine nucleotide exchange factors (GEF) have been implicated in direct activation of these GTPases. Here we have identified a new member of the Dbl family, GEF-H1, ... by screening a human HeLa cell cDNA library. GEF-H1 encodes a 100-kDa protein containing the conserved structural array of a Dbl homology domain in tandem with a pleckstrin homology domain and is most closely related to the lfc oncogene, but additionally it contains a unique coiled-coil domain at the carboxyl terminus. Biochemical analysis reveals that GEF-H1 is capable of stimulating guanine nucleotide exchange of Rac and Rho but is inactive toward Cdc42, TC10, or Ras. Moreover, GEF-H1 binds to Rac and Rho proteins in both the GDP- and guanosine 5'-3-O-(thio)triphosphate-bound states without detectable affinity for Cdc42 or Ras. Immunofluorescence reveals that GEF-H1 colocalizes with microtubules through the carboxyl-terminal coiled-coil domain. Overexpression of GEF-H1 in COS-7 cells results in induction of membrane ruffles. These results suggest that GEF-H1 may have a direct role in activation of Rac and/or Rho and in bringing the activated GTPase to specific target sites such as microtubules.
Mesh Terms:
3T3 Cells, Amino Acid Sequence, Animals, COS Cells, Enzyme Activation, Fluorescent Antibody Technique, GTP Phosphohydrolases, GTP-Binding Proteins, GTPase-Activating Proteins, Gene Library, Guanine Nucleotide Exchange Factors, Guanine Nucleotides, Humans, Mice, Microtubule-Associated Proteins, Molecular Sequence Data, Open Reading Frames, Proteins, Proto-Oncogene Proteins, Recombinant Proteins, Sequence Homology, Amino Acid, rac GTP-Binding Proteins, ras GTPase-Activating Proteins, ras Guanine Nucleotide Exchange Factors, rho GTP-Binding Proteins
3T3 Cells, Amino Acid Sequence, Animals, COS Cells, Enzyme Activation, Fluorescent Antibody Technique, GTP Phosphohydrolases, GTP-Binding Proteins, GTPase-Activating Proteins, Gene Library, Guanine Nucleotide Exchange Factors, Guanine Nucleotides, Humans, Mice, Microtubule-Associated Proteins, Molecular Sequence Data, Open Reading Frames, Proteins, Proto-Oncogene Proteins, Recombinant Proteins, Sequence Homology, Amino Acid, rac GTP-Binding Proteins, ras GTPase-Activating Proteins, ras Guanine Nucleotide Exchange Factors, rho GTP-Binding Proteins
J. Biol. Chem.
Date: Dec. 25, 1998
PubMed ID: 9857026
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