Oncogenic Dbl, Cdc42, and p21-activated kinase form a ternary signaling intermediate through the minimum interactive domains.
Activation of many Rho family GTPase pathways involves the signaling module consisting of the Dbl-like guanine nucleotide exchange factors (GEFs), the Rho GTPases, and the Rho GTPase specific effectors. The current biochemical model postulates that the GEF-stimulated GDP/GTP exchange of Rho GTPases leads to the active Rho-GTP species, and subsequently the active Rho GTPases interact with and activate the effectors. Here we report an unexpected finding that the Dbl oncoprotein, Cdc42 GTPase, and PAK1 can form a complex through their minimum functional motifs, i.e., the Dbl-homolgy (DH) and Pleckstrin-homology domains of Dbl, Cdc42, and the PBD domain of PAK1. The Dbl-Cdc42-PAK1 complex is sensitive to the nucleotide-binding state of Cdc42 since either dominant negative or constitutively active Cdc42 readily disrupts the ternary binding interaction. The complex formation depends on the interactions between the DH domain of Dbl and Cdc42 and between Cdc42 and the PBD domain of PAK1 and can be reconstituted in vitro by using the purified components. Furthermore, the Dbl-Cdc42-PAK1 ternary complex is active in generating signaling output through the activated PAK1 kinase in the complex. The GEF-Rho-effector ternary intermediate is also found in other Dbl-like GEF, Rho GTPase, and effector interactions. Finally, PAK1, through the PDB domain, is able to accelerate the GEF-induced GTP loading onto Cdc42. These results suggest that signal transduction through Cdc42 and possibly other Rho family GTPases could involve tightly coupled guanine nucleotide exchange and effector activation mechanisms and that Rho GTPase effector may have a feedback regulatory role in the Rho GTPase activation.
Wang
Lei
L
Division of Experimental Hematology, Children's Hospital Research Foundation, Graduate Program of Molecular Developmental Biology, University of Cincinnati, Cincinnati, Ohio 45229, USA.
Zhu
Kejin
K
Zheng
Yi
Y
D000818:Animals; D001798:Blood Proteins / Q000737:chemistry / Q000378:metabolism; D019556:COS Cells; D002522:Chlorocebus aethiops; D004357:Drug Synergism; D004789:Enzyme Activation; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D008958:Models, Molecular; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D017434:Protein Structure, Tertiary; D015682:Retroviridae Proteins, Oncogenic / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D040681:Structural Homology, Protein; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D054462:p21-Activated Kinases; D020741:rho GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology
D001798:Blood Proteins; D020662:Guanine Nucleotide Exchange Factors; D010750:Phosphoproteins; D015682:Retroviridae Proteins, Oncogenic; C039077:platelet protein P47; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020764:cdc42 GTP-Binding Protein; D020741:rho GTP-Binding Proteins