Phosphorylation of threonine 290 in the activation loop of Tpl2/Cot is necessary but not sufficient for kinase activity.
Cot/Tpl2/MAP3K8 is a serine/threonine kinase known to activate the ERK, p38, and JNK kinase pathways. Studies of Tpl2 knock-out mice reveal a clear defect in tumor necrosis factor-alpha production, although very little detail is known about its regulation and the signaling events involved. In the present study we demonstrated that phosphorylation of Cot was required for its maximal activity as phosphatase treatment of Cot decreased its kinase activity. The Cot sequence contains a conserved threonine at position 290 in the activation loop of the kinase domain. We found that mutation of this residue to alanine eliminated its ability to activate MEK/ERK and NF-kappaB pathways, whereas a phosphomimetic mutation to aspartic acid could rescue the ability to activate MEK. Thr-290 was also required for robust autophosphorylation of Cot. Antibody generated to phospho-Thr-290-Cot recognized both wild-type and kinase-dead Cot, suggesting that phosphorylation of Thr-290 did not occur through autophosphorylation but via another kinase. We showed that Cot was constitutively phosphorylated at Thr-290 in transfected human embryonic kidney 293T cells as well as human monocytes as this residue was phosphorylated in unstimulated and lipopolysaccharide-stimulated cells to the same degree. Treatment with herbimycin A inhibited Cot activity in the MEK/ERK pathway but did not inhibit phosphorylation at Thr-290. Together these results showed that phosphorylation of Cot at Thr-290 is necessary but not sufficient for full kinase activity in the MEK/ERK pathway.
Luciano
Brenda S
BS
Department of Molecular Inflammation, Inflammation Signaling, Wyeth Research, Cambridge, Massachusetts 02140, USA.
Hsu
Sang
S
Channavajhala
Padma L
PL
Lin
Lih-Ling
LL
Cuozzo
John W
JW
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001483:Base Sequence; D016227:Benzoquinones; D002460:Cell Line; D004247:DNA / Q000235:genetics; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D047029:Lactams, Macrocyclic; D008070:Lipopolysaccharides / Q000494:pharmacology; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017828:Rifabutin / Q000031:analogs & derivatives; D013912:Threonine / Q000737:chemistry; D014162:Transfection
D016227:Benzoquinones; D047029:Lactams, Macrocyclic; D008070:Lipopolysaccharides; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D011809:Quinones; D011994:Recombinant Proteins; D017828:Rifabutin; D013912:Threonine; C020754:herbimycin; D004247:DNA; D020930:MAP Kinase Kinase Kinases; C069937:MAP3K8 protein, human; C489843:Map3k8 protein, mouse