title: Ser-3 is important for regulating Mos interaction with and stimulation of mitogen-activated protein kinase kinase.
abstract: Mos is a germ cell-specific serine/threonine protein kinase that activates mitogen-activated protein kinase (MAPK) through MAPK kinase (MKK). In Xenopus oocytes, Mos synthesis is required for progesterone-induced activation of MAPK and maturation promoting factor. Injection of Mos or active MAPK causes mitotic arrest in early embryos, suggesting that Mos also acts via MKK and MAPK to induce the arrest of unfertilized eggs in metaphase of meiosis II. We have investigated whether Mos activity is regulated by phosphorylation. Previous studies have identified Ser-3 as the principal autophosphorylation site. We show that Mos interacts with the catalytic domain of MKK in a Saccharomyces cerevisiae two-hybrid test. Acidic substitutions of the sites phosphorylated by Mos in MKK reduce the interaction, implying that the complex may dissociate after phosphorylation of MKK by Mos. Furthermore, the Mos-MKK interaction requires Mos kinase activity, suggesting that Mos autophosphorylation may be involved in the interaction. Substitution of Ser-3 of Mos with Ala reduces the interaction with MKK and also reduces both the activation of MKK by Mos in vitro and cleavage arrest induced by Mos fusion protein in Xenopus embryos. By contrast, substitution of Ser-3 by Glu, an acidic amino acid that mimics phosphoserine, fosters the Mos interaction with MKK and permits activation of MKK in vitro and Mos-induced cleavage arrest. Moreover, the Glu-3 substitution increases the interaction of a kinase-inactive Mos mutant with MKK. Taken together, these results suggest that an important step in Mos activation involves the phosphorylation at Ser-3, which promotes Mos interaction with and activation of MKK.
authors.affiliation: Department of Biochemistry, University of Washington, Seattle 98195, USA.
authors.forename: M
authors.initials: M
authors.lastname: Chen
authors.forename: J A
authors.initials: JA
authors.lastname: Cooper
mesh_terms: D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D017930:Genes, Reporter; D015151:Immunoblotting; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000378:metabolism*; D017231:Proto-Oncogene Proteins c-mos / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D012694:Serine / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D014981:Xenopus / Q000196:embryology
chemical_list: D012694:Serine; D011494:Protein Kinases; D017231:Proto-Oncogene Proteins c-mos; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases