title: Protein phosphatase 1 regulates the phosphorylation state of the polarity scaffold Par-3.
abstract: Phosphorylation of the polarity protein Par-3 by the serine/threonine kinases aPKCzeta/iota and Par-1 (EMK1/MARK2) regulates various aspects of epithelial cell polarity, but little is known about the mechanisms by which these posttranslational modifications are reversed. We find that the serine/threonine protein phosphatase PP1 (predominantly the alpha isoform) binds Par-3, which localizes to tight junctions in MDCKII cells. PP1alpha can associate with multiple sites on Par-3 while retaining its phosphatase activity. By using a quantitative mass spectrometry-based technique, multiple reaction monitoring, we show that PP1alpha specifically dephosphorylates Ser-144 and Ser-824 of mouse Par-3, as well as a peptide encompassing Ser-885. Consistent with these observations, PP1alpha regulates the binding of 14-3-3 proteins and the atypical protein kinase C (aPKC) zeta to Par-3. Furthermore, the induced expression of a catalytically inactive mutant of PP1alpha severely delays the formation of functional tight junctions in MDCKII cells. Collectively, these results show that Par-3 functions as a scaffold, coordinating both serine/threonine kinases and the PP1alpha phosphatase, thereby providing dynamic control of the phosphorylation events that regulate the Par-3/aPKC complex.
authors.affiliation: Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, ON, Canada.
authors.forename: Andreas
authors.initials: A
authors.lastname: Traweger
authors.forename: Giselle
authors.initials: G
authors.lastname: Wiggin
authors.forename: Lorne
authors.initials: L
authors.lastname: Taylor
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Tate
authors.forename: Pavel
authors.initials: P
authors.lastname: Metalnikov
authors.forename: Tony
authors.initials: T
authors.lastname: Pawson
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002460:Cell Line; D004285:Dogs; D006801:Humans; D051379:Mice; D008954:Models, Biological; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D020033:Protein Isoforms; D051571:Protein Kinase C-alpha / Q000378:metabolism; D054645:Protein Phosphatase 1 / Q000502:physiology*; D012694:Serine / Q000737:chemistry; D019108:Tight Junctions / Q000378:metabolism
chemical_list: D048948:14-3-3 Proteins; D048868:Adaptor Proteins, Signal Transducing; D015815:Cell Adhesion Molecules; D018797:Cell Cycle Proteins; C115084:Pard3 protein, mouse; D020033:Protein Isoforms; D012694:Serine; D051571:Protein Kinase C-alpha; D054645:Protein Phosphatase 1; D010744:Phosphoric Monoester Hydrolases