Keap1 in adhesion complexes

Cell adhesion complexes are sensors that interact with the extracellular environment and allow for the transmission of signals found outside the cell across the plasma membrane to the cell interior. Keapl is a newly identified component of cell adhesion complexes. We investigated Keapl's association with these complexes in diverse tissues and cell types. Keapl is present in focal adhesion (FA)-like assemblies in kidney proximal tubule cells where it colocates with actin. In liver, Keapl is found in the adherens junctions (AJ) and at the base of the bile canaliculi. To study Keapl's involvement in both the integrin-based FA and the cadherin-based AJ, we induced formation of these complexes in fibroblasts, using a serum starvation followed by a serum supplementation method. When compared with vinculin, a component of all FA, we found that Keapl assembles only in the peripheral FA. Within the peripheral FA, Keapl was present in distinct foci along the length of the FA and these foci were different from vinculin, talin, paxillin, and phospho-tyrosine rich regions of the FA. Unlike most FA components, Keapl was also recruited to the newly formed AJ. As Keapl homologues are actin-bundling proteins, we hypothesize that Keapl's function is to bundle F-actin within these diverse types of cell adhesion components. (C) 2003 Wiley-Liss, Inc.