title: Rho-kinase phosphorylates PAR-3 and disrupts PAR complex formation.
abstract: A polarity complex of PAR-3, PAR-6, and atypical protein kinase C (aPKC) functions in various cell polarization events. PAR-3 directly interacts with Tiam1/Taim2 (STEF), Rac1-specific guanine nucleotide exchange factors, and forms a complex with aPKC-PAR-6-Cdc42*GTP, leading to Rac1 activation. RhoA antagonizes Rac1 in certain types of cells. However, the relationship between RhoA and the PAR complex remains elusive. We found here that Rho-kinase/ROCK/ROK, the effector of RhoA, phosphorylated PAR-3 at Thr833 and thereby disrupted its interaction with aPKC and PAR-6, but not with Tiam2. Phosphorylated PAR-3 was observed in the leading edge, and in central and rear portions of migrating cells having front-rear polarity. Knockdown of PAR-3 by small interfering RNA (siRNA) impaired cell migration, front-rear polarization, and PAR-3-mediated Rac1 activation, which were recovered with siRNA-resistant PAR-3, but not with the phospho-mimic PAR-3 mutant. We propose that RhoA/Rho-kinase inhibits PAR complex formation through PAR-3 phosphorylation, resulting in Rac1 inactivation.
authors.affiliation: Department of Cell Pharmacology, Graduate School of Medicine, Nagoya University, 65 Tsurumai, Showa-ku, Nagoya, Aichi 466-8550, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Nakayama
authors.forename: Takaaki M
authors.initials: TM
authors.lastname: Goto
authors.forename: Masayuki
authors.initials: M
authors.lastname: Sugimoto
authors.forename: Takashi
authors.initials: T
authors.lastname: Nishimura
authors.forename: Takafumi
authors.initials: T
authors.lastname: Shinagawa
authors.forename: Sigeo
authors.initials: S
authors.lastname: Ohno
authors.forename: Mutsuki
authors.initials: M
authors.lastname: Amano
authors.forename: Kozo
authors.initials: K
authors.lastname: Kaibuchi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002465:Cell Movement; D016764:Cell Polarity; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000378:metabolism*; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism; D051381:Rats; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D054460:rho-Associated Kinases / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D046912:Multiprotein Complexes; D010769:Phosphothreonine; D054460:rho-Associated Kinases; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein