MEKK2 associates with the adapter protein Lad/RIBP and regulates the MEK5-BMK1/ERK5 pathway.
MEKK2 and MEKK3 are two closely related mitogen-activated protein kinase (MAPK) kinase kinases. The kinase domains of MEKK2 and MEKK3 are nearly identical, although their N-terminal regulatory domains are significantly divergent. By yeast two-hybrid library screening, we have identified MEK5, the MAPK kinase in the big mitogen-activated protein kinase 1 ... (BMK1)/ERK5 pathway, as a binding partner for MEKK2. MEKK2 expression stimulates BMK1/ERK5 activity, the downstream substrate for MEK5. Compared with MEKK3, MEKK2 activated BMK1/ERK5 to a greater extent, which might correlate with a higher affinity MEKK2-MEK5 interaction. A dominant negative form of MEK5 blocked the activation of BMK1/ERK5 by MEKK2, whereas activation of c-Jun N-terminal kinase (JNK) was unaffected, showing that MEK5 is a specific downstream effector of MEKK2 in the BMK1/ERK5 pathway. Activation of BMK1/ERK5 by epidermal growth factor and H2O2 in Cos7 and HEK293 cells was completely blocked by a kinase-inactive MEKK3 (MEKK3kin(-)), whereas MEKK2kin(-) had no effect. However, in D10 T cells, expression of MEKK2kin(-) but not MEKK3kin(-) inhibited BMK1/ERK5 activity. Two-hybrid screening also identified Lck-associated adapter/Rlk- and Itk-binding protein (Lad/RIBP), a T cell adapter protein, as a binding partner for MEKK2. MEKK2 and Lad/RIBP colocalize at the T cell contact site with antigen-loaded presenting cells, demonstrating cotranslocation of MEKK2 and Lad/RIBP during T cell activation. MEKK3 neither binds Lad/RIBP nor is recruited to the T cell contact with antigen presenting cell. MEKK2 and MEKK3 are differentially associated with signaling from specific upstream receptor systems, whereas both activate the MEK5-BMK1/ERK5 pathway.
Mesh Terms:
Adaptor Proteins, Signal Transducing, Animals, Antigen-Presenting Cells, COS Cells, Carrier Proteins, Cell Line, Epidermal Growth Factor, Humans, Hydrogen Peroxide, Lymphocyte Activation, MAP Kinase Kinase 5, MAP Kinase Kinase Kinase 2, MAP Kinase Kinase Kinase 3, MAP Kinase Kinase Kinases, MAP Kinase Signaling System, Mitogen-Activated Protein Kinase 7, Mitogen-Activated Protein Kinase Kinases, Mitogen-Activated Protein Kinases, Mutation, Oxidants, T-Lymphocytes, Transfection, Two-Hybrid System Techniques
Adaptor Proteins, Signal Transducing, Animals, Antigen-Presenting Cells, COS Cells, Carrier Proteins, Cell Line, Epidermal Growth Factor, Humans, Hydrogen Peroxide, Lymphocyte Activation, MAP Kinase Kinase 5, MAP Kinase Kinase Kinase 2, MAP Kinase Kinase Kinase 3, MAP Kinase Kinase Kinases, MAP Kinase Signaling System, Mitogen-Activated Protein Kinase 7, Mitogen-Activated Protein Kinase Kinases, Mitogen-Activated Protein Kinases, Mutation, Oxidants, T-Lymphocytes, Transfection, Two-Hybrid System Techniques
J. Biol. Chem.
Date: Feb. 16, 2001
PubMed ID: 11073940
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