title: Identification of MEKK2/3 serine phosphorylation site targeted by the Toll-like receptor and stress pathways.
abstract: Members of the mitogen-activated protein kinase kinase kinase (MAP3K) family are crucial for the Toll-like receptor (TLR) signaling and cellular stress responses. However, the molecular mechanisms underlying the TLR- and cellular stress-mediated MAP3K activation remain largely unknown. In this study, we identified a key regulatory phosphorylation site, serine 519 and serine 526, in MAP3K MEKK2 and MEKK3, respectively. Mutation of this serine to an alanine severely impaired MEKK2/3 activation. We generated an anti-p-MEKK2/3 antibody and used this antibody to demonstrate that lipopolysaccharide induced MEKK2 and MEKK3 phosphorylation on their regulatory serine. We found that the serine phosphorylation was crucial for TLR-induced interleukin 6 production and this process is regulated by TRAF6, a key adaptor molecule for the TLR pathway. We further demonstrated that many, but not all, MAPK agonists induced the regulatory serine phosphorylation, suggesting an involvement of different MAP3Ks in activation of the MAPK cascades leading to different cellular responses. In conclusion, this study reveals a novel molecular mechanism for MEKK2/3 activation by the TLR and cellular stress pathways.
authors.affiliation: Department of Immunology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030-1903, USA.
authors.forename: Dongyu
authors.initials: D
authors.lastname: Zhang
authors.forename: Valeria
authors.initials: V
authors.lastname: Facchinetti
authors.forename: Xiaofang
authors.initials: X
authors.lastname: Wang
authors.forename: Qiaojia
authors.initials: Q
authors.lastname: Huang
authors.forename: Jun
authors.initials: J
authors.lastname: Qin
authors.forename: Bing
authors.initials: B
authors.lastname: Su
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D045163:Antibodies, Phospho-Specific / Q000276:immunology; D016207:Cytokines / Q000378:metabolism; D004789:Enzyme Activation; D015850:Interleukin-6 / Q000378:metabolism; D008024:Ligands; D008070:Lipopolysaccharides / Q000494:pharmacology; D048730:MAP Kinase Kinase Kinase 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D048748:MAP Kinase Kinase Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D019606:Phosphoamino Acids / Q000032:analysis / Q000276:immunology; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012694:Serine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D051193:Toll-Like Receptors / Q000378:metabolism*
chemical_list: D045163:Antibodies, Phospho-Specific; D016207:Cytokines; D015850:Interleukin-6; D008024:Ligands; D008070:Lipopolysaccharides; D019606:Phosphoamino Acids; D047428:Protein Kinase Inhibitors; D048029:TNF Receptor-Associated Factor 6; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D012694:Serine; D048730:MAP Kinase Kinase Kinase 2; D048748:MAP Kinase Kinase Kinase 3