MEKK2 is required for T-cell receptor signals in JNK activation and interleukin-2 gene expression.
The c-Jun N-terminal kinases (JNKs) are members of the mitogen-activated protein kinase (MAPK) gene family and are essential for cell proliferation, differentiation, and apoptosis. Previously we found that activation of JNK in T-cells required costimulation of both T-cell receptor and auxiliary receptors such as CD28. In this study, we cloned a full-length human MEK kinase (MEKK) 2 cDNA from Jurkat T-cells and demonstrated that it was a major upstream MAPK kinase kinase for the JNK cascade in T-cells. The human MEKK2 cDNA encoded a polypeptide of 619 amino acids and was the human counterpart of the reported murine MEKK2. It was 94% homologous with human and murine MEKK3 at the catalytic domains and 60% homologous at the N-terminal noncatalytic region. Northern blot analysis showed that MEKK2 was ubiquitously expressed, with the highest level in peripheral blood leukocytes. In T cells, MEKK2 was found to be a strong activator of JNK but not of extracellular signal-regulated kinase MAPKs and to activate JNK-dependent AP-1 reporter gene expression. MEKK2 also synergized with anti-CD3 antibody to activate JNK in T cells, and stimulation of T cells led to induction of MEKK2 tyrosine phosphorylation. Significantly, the JNK activation induced by anti-CD3 and anti-CD28 antibodies, but not by 12-O-tetradecanoylphorbol-13-acetate and Ca(2+) ionophore A23187, was inhibited by dominant negative MEKK2 mutants. AP-1 and interleukin-2 reporter gene induction in T-cells was also inhibited by dominant negative MEKK2 mutants. Taken together, our results showed that human MEKK2 is a key signaling molecule for T-cell receptor/CD3-mediated JNK MAPK activation and interleukin-2 gene expression.
Department of Immunology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA. bingsu@odin.mdacc.tmc.edu
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D004789:Enzyme Activation; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D007376:Interleukin-2 / Q000235:genetics*; D048031:JNK Mitogen-Activated Protein Kinases; D048730:MAP Kinase Kinase Kinase 2; D020930:MAP Kinase Kinase Kinases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008969:Molecular Sequence Data; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D015533:Transcriptional Activation
D017931:DNA Primers; D007376:Interleukin-2; D011948:Receptors, Antigen, T-Cell; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048730:MAP Kinase Kinase Kinase 2; D020930:MAP Kinase Kinase Kinases; C482618:MAP3K2 protein, human; C482619:Map3k2 protein, mouse