title: MEKK2 associates with the adapter protein Lad/RIBP and regulates the MEK5-BMK1/ERK5 pathway.
abstract: 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.
authors.affiliation: Department of Pharmacology, University of Colorado Health Sciences Center and University of Colorado Cancer Center, Denver, CO 80262, USA.
authors.forename: W
authors.initials: W
authors.lastname: Sun
authors.forename: K
authors.initials: K
authors.lastname: Kesavan
authors.forename: B C
authors.initials: BC
authors.lastname: Schaefer
authors.forename: T P
authors.initials: TP
authors.lastname: Garrington
authors.forename: M
authors.initials: M
authors.lastname: Ware
authors.forename: N L
authors.initials: NL
authors.lastname: Johnson
authors.forename: E W
authors.initials: EW
authors.lastname: Gelfand
authors.forename: G L
authors.initials: GL
authors.lastname: Johnson
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008213:Lymphocyte Activation; D048671:MAP Kinase Kinase 5; D048730:MAP Kinase Kinase Kinase 2; D048748:MAP Kinase Kinase Kinase 3; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism / Q000502:physiology*; D020935:MAP Kinase Signaling System; D048054:Mitogen-Activated Protein Kinase 7; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009154:Mutation; D016877:Oxidants / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D014162:Transfection; D020798:Two-Hybrid System Techniques
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D016877:Oxidants; C402726:Sh2d2a protein, mouse; D004815:Epidermal Growth Factor; D006861:Hydrogen Peroxide; D048054:Mitogen-Activated Protein Kinase 7; D020928:Mitogen-Activated Protein Kinases; D048730:MAP Kinase Kinase Kinase 2; D048748:MAP Kinase Kinase Kinase 3; D020930:MAP Kinase Kinase Kinases; C482618:MAP3K2 protein, human; C482625:MAP3K3 protein, human; C482619:Map3k2 protein, mouse; C482626:Map3k3 protein, mouse; D048671:MAP Kinase Kinase 5; C482563:MAP2K5 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases