title: Bardet-Biedl syndrome proteins control the cilia length through regulation of actin polymerization.
abstract: Primary cilia are cellular appendages important for signal transduction and sensing the environment. Bardet-Biedl syndrome proteins form a complex that is important for several cytoskeleton-related processes such as ciliogenesis, cell migration and division. However, the mechanisms by which BBS proteins may regulate the cytoskeleton remain unclear. We discovered that Bbs4- and Bbs6-deficient renal medullary cells display a characteristic behaviour comprising poor migration, adhesion and division with an inability to form lamellipodial and filopodial extensions. Moreover, fewer mutant cells were ciliated [48% ± 6 for wild-type (WT) cells versus 23% ± 7 for Bbs4 null cells; P < 0.0001] and their cilia were shorter (2.55 μm ± 0.41 for WT cells versus 2.16 μm ± 0.23 for Bbs4 null cells; P < 0.0001). While the microtubular cytoskeleton and cortical actin were intact, actin stress fibre formation was severely disrupted, forming abnormal apical stress fibre aggregates. Furthermore, we observed over-abundant focal adhesions (FAs) in Bbs4-, Bbs6- and Bbs8-deficient cells. In view of these findings and the role of RhoA in regulation of actin filament polymerization, we showed that RhoA-GTP levels were highly upregulated in the absence of Bbs proteins. Upon treatment of Bbs4-deficient cells with chemical inhibitors of RhoA, we were able to restore the cilia length and number as well as the integrity of the actin cytoskeleton. Together these findings indicate that Bbs proteins play a central role in the regulation of the actin cytoskeleton and control the cilia length through alteration of RhoA levels.
authors.forename: Victor
authors.initials: V
authors.lastname: Hernandez-Hernandez
authors.forename: Priyanka
authors.initials: P
authors.lastname: Pravincumar
authors.forename: Anna
authors.initials: A
authors.lastname: Diaz-Font
authors.forename: Helen
authors.initials: H
authors.lastname: May-Simera
authors.forename: Dagan
authors.initials: D
authors.lastname: Jenkins
authors.forename: Martin
authors.initials: M
authors.lastname: Knight
authors.forename: Philip L
authors.initials: PL
authors.lastname: Beales
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry / Q000378:metabolism; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D020788:Bardet-Biedl Syndrome / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002923:Cilia / Q000378:metabolism* / Q000648:ultrastructure*; D003598:Cytoskeletal Proteins; D004847:Epithelial Cells / Q000378:metabolism; D022001:Focal Adhesions / Q000378:metabolism; D056385:Group II Chaperonins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins; D041681:NIH 3T3 Cells; D010641:Phenotype; D058105:Polymerization; D055503:Protein Multimerization; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000199:Actins; C429655:BBS4 protein, human; D003598:Cytoskeletal Proteins; C414726:MKKS protein, human; D008869:Microtubule-Associated Proteins; D011506:Proteins; C478138:TTC8 protein, human; D029961:Zebrafish Proteins; C552737:ttc8 protein, zebrafish; D056385:Group II Chaperonins; D020742:rhoA GTP-Binding Protein