ABSTRACT
Docking proteins are substrates of tyrosine kinases and function in the recruitment and assembly of specific signal transduction molecules. Here we found that p62dok family members act as substrates for the c-Ret receptor tyrosine kinase. In addition to dok-1, dok-2, and dok-3, we identified two new family members, dok-4 and dok-5, that can directly associate with Y1062 of c-Ret. Dok-4 and dok-5 constitute a subgroup of dok family members that is coexpressed with c-Ret in various neuronal tissues. Activated c-Ret promotes neurite outgrowth of PC12 cells; for this activity, Y1062 in c-Ret is essential. c-Ret/dok fusion proteins, in which Y1062 of c-Ret is deleted and replaced by the sequences of dok-4 or dok-5, induce ligand-dependent axonal outgrowth of PC12 cells, whereas a c-Ret fusion containing dok-2 sequences does not elicit this response. Dok-4 and dok-5 do not associate with rasGAP or Nck, in contrast to p62dok and dok-2. Moreover, dok-4 and dok-5 enhance c-Ret-dependent activation of mitogen-activated protein kinase. Thus, we have identified a subclass of p62dok proteins that are putative links with downstream effectors of c-Ret in neuronal differentiation.
Subject(s)
Adaptor Proteins, Signal Transducing , Carrier Proteins/metabolism , DNA-Binding Proteins , Drosophila Proteins , Intracellular Signaling Peptides and Proteins , Neurons/metabolism , Phosphoproteins/genetics , Proto-Oncogene Proteins/metabolism , RNA-Binding Proteins , Receptor Protein-Tyrosine Kinases/metabolism , Amino Acid Sequence , Animals , Carrier Proteins/genetics , Carrier Proteins/pharmacology , Cell Differentiation/drug effects , Cell Differentiation/physiology , DNA, Complementary/genetics , DNA, Complementary/isolation & purification , Embryo, Mammalian , Mice , Molecular Sequence Data , Multigene Family , Neurites/drug effects , Neurons/cytology , Organ Specificity , PC12 Cells , Phosphoproteins/metabolism , Phosphorylation , Proto-Oncogene Proteins c-ret , Rats , Receptor, TIE-2 , Sequence Homology, Amino Acid , Signal Transduction/physiology , Two-Hybrid System Techniques , ras GTPase-Activating Proteins/metabolismABSTRACT
Interactions between beta-catenin and LEF-1/TCF, APC and conductin/axin are essential for wnt-controlled stabilization of beta-catenin and transcriptional activation. The wnt signal transduction pathway is important in both embryonic development and tumor progression. We identify here amino acid residues in beta-catenin that distinctly affect its binding to LEF-1/TCF, APC and conductin. These residues form separate surface clusters, termed hot spots, along the armadillo superhelix of beta-catenin. We also show that complementary charged and hydrophobic amino acids are required for formation of the bipartite beta-catenin-LEF-1 transcription factor. Moreover, we demonstrate that conductin/axin binding to beta-catenin is essential for beta-catenin degradation, and that APC acts as a cofactor of conductin/axin in this process. Binding of APC to conductin/axin activates the latter and occurs between their SAMP and RGS domains, respectively.
