Association of CNK1 with Rho guanine nucleotide exchange factors controls signaling specificity downstream of Rho.
BACKGROUND
Rho is a small GTPase that controls signal transduction pathways in response to a large number of extracellular stimuli. With over 15 potential Rho target proteins identified to date, however, it is not clear how distinct signaling outputs can be generated downstream of a particular stimulus.


RESULTS
Several of the known Rho targets are structurally reminiscent of scaffold proteins, which are generally thought to play an important role in controlling signaling specificity. Here, we show that the Rho target CNK1 is a scaffold protein that interacts with Net1 or p115RhoGEF, two Rho-specific guanine nucleotide exchange factors (GEFs), as well with MLK2 and MKK7, two of the kinase components in the JNK MAP kinase cascade. CNK1 acts cooperatively with the two GEFs to activate JNK MAP kinase, but not other Rho-mediated pathways. In HeLa cells, serum or sphingosine-1-phosphate stimulate Rho-dependent activation of the JNK MAP kinase cascade, and this requires endogenous CNK1.


CONCLUSIONS
We conclude that CNK1 couples a subset of Rho exchange factors to activation of the JNK MAP kinase pathway and that signaling specificity is achieved through complexes containing both upstream activators and downstream targets of Rho.
Jaffe
Aron B
AB
Medical Research Council Laboratory for Molecular Cell Biology, Cancer Research UK Oncogene and Signal Transduction Group and Department of Biochemistry, University College London, London WC1E 6BT, United Kingdom.
Hall
Alan
A
Schmidt
Anja
A
D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D005982:Glutathione Transferase; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008156:Luciferases; D048688:MAP Kinase Kinase 7 / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D034521:Nuclear Matrix-Associated Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
C500833:CNKSR1 protein, human; D020662:Guanine Nucleotide Exchange Factors; D047908:Intracellular Signaling Peptides and Proteins; D034521:Nuclear Matrix-Associated Proteins; D008156:Luciferases; D005982:Glutathione Transferase; D048031:JNK Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; C093290:MAP3K10 protein, human; D048688:MAP Kinase Kinase 7; C482569:MAP2K7 protein, human; D020741:rho GTP-Binding Proteins