Novel regulatory mechanisms for the Dbl family guanine nucleotide exchange factor Cool-2/alpha-Pix.
The Cool-2 (cloned-out of library-2) protein (identical to alpha-Pix for Pak-interactive exchange factor) has been implicated in various biological responses including chemoattractant signaling and in certain forms of mental retardation. We show that when Cool-2 exists as a dimer, it functions as a Rac-specific guanine nucleotide exchange factor (GEF). Dimerization of Cool-2 enables its Dbl (diffuse B-cell lymphoma) and pleckstrin homology domains to work together (in trans) to bind specifically to Rac-GDP. Dissociation of dimeric Cool-2 into its monomeric form allows it to act as a GEF for Cdc42 as well as for Rac. The binding of either PAK (p21-activated kinase) or Cbl (Casitas B-lymphoma) to the SH3 domain of monomeric Cool-2 is necessary for the functional interactions between GDP-bound Cdc42 or Rac and the Cool-2 monomer. The betagamma subunit complex of large GTP-binding proteins, by interacting with PAK, stimulates the dissociation of the Cool-2 dimer and activates its GEF activity for Cdc42. Overall, these findings highlight novel mechanisms by which extracellular signals can direct the specific activation of Rac versus Cdc42 by Cool-2/alpha-Pix.
Feng
Qiyu
Q
Department of Molecular Medicine, Cornell University, Ithaca, NY 14853-6401, USA.
Baird
Daniel
D
Cerione
Richard A
RA
D000818:Animals; D019556:COS Cells; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008954:Models, Biological; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D064067:Rho Guanine Nucleotide Exchange Factors; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D018909:src Homology Domains
D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D011994:Recombinant Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins