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- Title
Slit-Diaphragm Protein FAT1 Regulates Directed Actin Polymerization and Is Essential for the Establishment of Planar Cell Polarity.
- Authors
Moeller, M. J.; Braun, G. S.; Dau, C.; Kuszka, A.; Holzman, L. B.; Kriz, W.
- Abstract
Objective: FAT1 is a large transmembrane protocadherin highly expressed at the slit-diaphragm in podocyte foot-processes. FAT1 deficient mice die perinatally because of massive proteinuria. Ultrastructural analysis demonstrated that the primary defect was located in podocytes that have lost their ability to form actin-based interdigitating foot processes bridged by a slit-diaphragm. In this study, we have undertaken the first investigation of the molecular function of FAT1. Results: Several antisera against FAT1 were raised. In cultured cells, FAT1 was localized at the leading edge of lamellipodial protrusions and in filopodia, both of which are structures based on directed actin polymerization. Indeed, we were able to establish a direct interaction of FAT1 with regulatory proteins of directed actin polymerization: the Ena/VASP proteins. This interaction occurred in an EVH1-domain dependent fashion via a novel tandem repeat of EVH1-binding motifs in the cytoplasmic tail of FAT1. In accordance with our in vitro binding assays, FAT1 and Ena/VASP proteins co-localized in cultured cells. The functional significance of the FAT1-Ena/VASP interaction was investigated using a combination of RNA interference and a lentiviral transduction system. Our experiments indicated that FAT1 deficient cells exhibit a similar phenotype to cells with altered Ena/ VASP function. In addition, FAT1 deficient cells were evaluated in a wound assay. FAT1 deficient cells had lost their ability to polarize towards the denuded area and to migrate into the wound. Using a second experimental approach, we were able to confirm that FAT1 acts as an essential receptor for the orientation of cells in the horizontal plane of epithelia cells (planar cell polarity). Conclusions: These findings have important implications for our understanding of the molecular mechanisms at the slit-diaphragm as well as for the young field of planar cell polarity.
- Subjects
CADHERINS; PROTEINURIA; ACTIN; POLYMERIZATION; CELLS
- Publication
Kidney & Blood Pressure Research, 2004, Vol 27, Issue 5/6, p300
- ISSN
1420-4096
- Publication type
Article