Caenorhabditis elegans CNK-1 promotes Raf activation but is not essential for Ras/Raf signaling.
Connector enhancer of Ksr (CNK) is a conserved multidomain protein essential for Ras signaling in Drosophila melanogaster and thought to be involved in Raf kinase activation. However, the precise role of CNK in Ras signaling is not known, and mammalian CNKs are proposed to have distinct functions. Caenorhabditis elegans has a single CNK homologue, cnk-1. Here, we describe the role of cnk-1 in C. elegans Ras signaling and its requirements for LIN-45 Raf activation. We find that cnk-1 positively regulates multiple Ras signaling events during development, but, unlike Drosophila CNK, cnk-1 does not appear to be essential for signaling. cnk-1 mutants appear to be normal but show cell-type-specific genetic interactions with mutations in two other Ras pathway scaffolds/adaptors ksr-1 and sur-8. Genetic epistasis using various activated LIN-45 Raf transgenes shows that CNK-1 promotes LIN-45 Raf activation at a step between the dephosphorylation of inhibitory sites in the regulatory domain and activating phosphorylation in the kinase domain. Our data are consistent with a model in which CNK promotes Raf phosphorylation/activation through membrane localization, oligomerization, or association with an activating kinase.
Rocheleau
Christian E
CE
Department of Genetics, University of Pennsylvania, Philadelphia, PA 19104-6145, USA.
Rönnlund
Agneta
A
Tuck
Simon
S
Sundaram
Meera V
MV
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D048490:raf Kinases / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C504803:CNK-1 protein, C elegans; D029742:Caenorhabditis elegans Proteins; D047908:Intracellular Signaling Peptides and Proteins; C113520:soc-2 protein, C elegans; D011494:Protein Kinases; C097199:KSR-1 protein kinase; C454817:lin-45 protein, C elegans; D048490:raf Kinases; D018631:ras Proteins