title: Regulated protein-protein interaction between aPKC and PAR-3 plays an essential role in the polarization of epithelial cells.
abstract: BACKGROUND
  Recent studies have revealed that aPKC (atypical protein kinase C), PAR-3 and PAR-6 play indispensable roles in the regulation of various cell polarization events, from worms to mammals, suggesting that they comprise an evolutionarily conserved protein machinery which is essential for cell polarization. The three proteins interact with each other to form a ternary complex and thus mutually regulate their functionality and localization. Here, we investigated the biochemical nature of the aPKC-PAR-3 interaction in detail to clarify its functional importance in cell polarity.
  
  
  RESULTS
  The highly conserved 26 amino acid sequence 816-841, in PAR-3 was found to be necessary and sufficient for the tight association with aPKC. Among several conserved serine/threonine residues within the region, aPKC preferentially phosphorylates serine-827 in vitro, and this phosphorylation reduces the stability of the PAR-3-aPKC interaction. Several analyses using a phospho-serine 827 specific antibody have established that this phosphorylation by aPKC occurs in vivo. Over-expression of a point mutant of PAR-3 (S827A), which is predicted to form a stable complex with aPKC, causes defects in the cell-cell contact-induced cell polarization of epithelial MDCK cells, similarly to a dominant negative mutant of aPKC.
  
  
  CONCLUSIONS
  These results imply that serine 827 in the aPKC binding site of PAR-3 is a target of aPKC and that the regulated interaction between a protein kinase, aPKC, and its substrate, PAR-3, plays an essential role in the establishment of cell polarity.
authors.affiliation: Department of Molecular Biology, Yokohama City University School of Medicine, Yokohama 236-0004, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Nagai-Tamai
authors.forename: Keiko
authors.initials: K
authors.lastname: Mizuno
authors.forename: Tomonori
authors.initials: T
authors.lastname: Hirose
authors.forename: Atsushi
authors.initials: A
authors.lastname: Suzuki
authors.forename: Shigeo
authors.initials: S
authors.lastname: Ohno
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D017124:Conserved Sequence; D066298:In Vitro Techniques; D010766:Phosphorylation; D017354:Point Mutation; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases
chemical_list: D029742:Caenorhabditis elegans Proteins; C097238:PAR-3 protein, C elegans; D017346:Protein Serine-Threonine Kinases; C115015:PKC-3 protein; D011493:Protein Kinase C