Defects in cytokinesis, actin reorganization and the contractile vacuole in cells deficient in RhoGDI.
Rho GDP-dissociation inhibitors (RhoGDIs) modulate the cycling of Rho GTPases between active GTP-bound and inactive GDP-bound states. We identified two RhoGDI homologues in DICTYOSTELIUM: GDI1 shares 51-58% similarity to RhoGDIs from diverse species. GDI2 is more divergent (40-44% similarity) and lacks the N-terminal regulatory arm characteristic for RhoGDI proteins. Both are cytosolic proteins and do not relocalize upon reorganization of the actin cytoskeleton. Using a two-hybrid approach, we identified Rac1a/1b/1c, RacB, RacC and RacE as interacting partners for GDI1. Cells lacking GDI1 are multinucleate, grow slowly and display a moderate pinocytosis defect, but rates of phagocytosis are unaffected. Mutant cells present prominent actin-rich protrusions, and large vacuoles that are continuous with the contractile vacuole system. The actin polymerization response upon stimulation with cAMP was reduced, but the motile behavior toward the chemoattractant was unaffected. Our results indicate that GDI1 plays a central role in the regulation of signal transduction cascades mediated by Rho GTPases.
Institut für Biochemie I, Medizinische Fakultät, University of Cologne, Joseph-Stelzmann-Strasse 52, D-50931 Köln, Germany. francisco.rivero@uni-koeln.de
Francisco
F
Rivero
Daria
D
Illenberger
Baggavalli P
BP
Somesh
Heidrun
H
Dislich
Nicola
N
Adam
Ann-Kathrin
AK
Meyer
D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001704:Biopolymers; D002455:Cell Division / Q000235:genetics*; D002633:Chemotaxis / Q000502:physiology; D003572:Cytochalasins / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D004023:Dictyostelium / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000235:genetics / Q000502:physiology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013045:Species Specificity; D020798:Two-Hybrid System Techniques; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism; D014617:Vacuoles / Q000502:physiology*; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors
D000199:Actins; D001704:Biopolymers; D003572:Cytochalasins; D020730:Guanine Nucleotide Dissociation Inhibitors; D015800:Protozoan Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; C031218:cytochalasin A; D025262:Vacuolar Proton-Translocating ATPases; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins