title: Cilia movement regulates expression of the Raf-1 kinase inhibitor protein.
abstract: Renal epithelial cell primary cilia act as mechanosensors in response to changes in luminal fluid flow. To determine the role of cilia bending in the mechanosensory function of cilia, we performed proteomic analysis of collecting duct cell lines with or without cilia that were kept stationary or rotated to stimulate cilia bending. Expression of the Raf-1 kinase inhibitor protein (RKIP), an inhibitor of the MAPK pathway, was significantly elevated in rotated cilia (+) cells. This was compared with RKIP levels in cilia (-) cells that were stationary or rotated as well as in cilia (+) cells that were stationary. This result was confirmed in cilia knockout adult mice that had lower renal RKIP levels compared with adult mice with cilia. Downstream of RKIP, expression of phosphorylated ERK was decreased only in cells that had cilia and were subjected to constant cilia bending. Furthermore, elevated RKIP levels were associated with reduced cell proliferation. Blockade of PKC abrogated ciliary bending-induced increases in RKIP. In summary, we found that ciliary movement may help control the expression of the Raf-1 kinase inhibitor protein and thus maintain cell differentiation. In terms of polycystic kidney disease, loss of cilia and therefore sensitivity to flow may lead to reduced RKIP levels, activation of the MAPK pathway, and contribute to the formation of cysts.
authors.affiliation: Ralph H. Johnson Veterans Affairs Medical Center, Medical University of South Carolina, Charleston, 29425, USA.
authors.forename: Kelli M
authors.initials: KM
authors.lastname: Sas
authors.forename: Michael G
authors.initials: MG
authors.lastname: Janech
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Favre
authors.forename: John M
authors.initials: JM
authors.lastname: Arthur
authors.forename: P Darwin
authors.initials: PD
authors.lastname: Bell
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D049109:Cell Proliferation; D002923:Cilia / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D049488:Phosphatidylethanolamine Binding Protein / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D040901:Proteomics; D012399:Rotation; D013997:Time Factors; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
chemical_list: D049488:Phosphatidylethanolamine Binding Protein; D047428:Protein Kinase Inhibitors; C539308:Raf kinase inhibitory protein, mouse; C490898:Tg737Rpw protein, mouse; D025521:Tumor Suppressor Proteins; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases