title: MEK inhibition and phosphorylation of serine 4 on B23 are two coincident events in mitosis.
abstract: Previous studies have shown that activation of the Raf/MEK/ERK pathway is necessary for G2/M transition. However, as for the activation state of MEK in mitosis the conclusion is not consistent. Here we show that MEK is inhibited in mitosis. In addition, we identify a multifunctional protein named B23 that strongly cross-reacts with a phospho-MEK antibody in mitotic cells. Sequence homology between the N-terminus surrounding Ser 4 of B23 and the Raf phosphorylation site on MEK suggests a mechanism for cross-reaction of the antibody. Thus, mutation of Ser 4 to alanine abolishes cross-reactivity between B23 and the phospho-MEK antibody. Our findings may explain the discrepancy of results obtained with the use of phospho-MEK antibody regarding the activation state of MEK in mitosis.
authors.affiliation: Diabetes Research Unit, Section of Endocrinology, Department of Medicine, Boston University School of Medicine, Boston, MA 02118, USA.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Hayne
authors.forename: Xiaoqin
authors.initials: X
authors.lastname: Xiang
authors.forename: Zhijun
authors.initials: Z
authors.lastname: Luo
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D045163:Antibodies, Phospho-Specific / Q000378:metabolism; D019556:COS Cells; D002522:Chlorocebus aethiops; D003429:Cross Reactions; D004789:Enzyme Activation; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008938:Mitosis; D041681:NIH 3T3 Cells; D009687:Nuclear Proteins / Q000276:immunology / Q000378:metabolism*; D000090243:Nucleophosmin; D010766:Phosphorylation; D012694:Serine / Q000378:metabolism*
chemical_list: D000906:Antibodies; D045163:Antibodies, Phospho-Specific; D008565:Membrane Proteins; C000715570:Npm1 protein, mouse; D009687:Nuclear Proteins; D000090243:Nucleophosmin; D012694:Serine; D020929:Mitogen-Activated Protein Kinase Kinases