THE ASSOCIATION OF TAU-LIKE PROTEINS WITH VIMENTIN FILAMENTS IN CULTURED-CELLS

There is increasing evidence that the different polymers that constitu te the cytoskeleton are interconnected to form a three dimensional net work. The macromolecular interaction patterns that stabilize this netw ork and its intrinsic dynamics are the basis for numerous cellular pro cesses. Within this context, in vitro studies have pointed to the exis tence of specific associations between microtubules, microfilaments, a nd intermediate filaments. It has also been postulated that microtubul e-associated proteins (MAPs) are directly involved in mediating these interactions. The interactions of tau with vimentin filaments, and its relationships with other filaments of the cytoskeletal network, were analyzed in SW-13 adenocarcinoma cells, through an integrated approach that included biochemical and immunological studies. This cell line h as the advantage of presenting a wild-type clone (vim+) and a mutant c lone (vim-) which is deficient in vimentin expression. We analyzed the cellular roles of tau, focusing on its interactions with vimentin fil aments, within the context of its functional aspects in the organizati on of the cytoskeletal network. Cosedimentation experiments of microtu bular protein with vimentin in cell extracts enriched in intermediate filaments, combined with studies on the direct interaction of tau with nitrocellulose-bound vimentin and analysis of tau binding to vimentin immobilized in single-strand DNA affinity columns, indicate that tau interacts with the vimentin network. These studies were conformed by a quantitative analysis of the immunofluorescence patterns of cytoskele ton-associated tubulin, tau, and vimentin using how cytometry. In this regard, a decrease in the levels of tau associated to the cytoskeleta l network in the vim-cell mutant compared with the wild-type clones wa s observed. However, immunofluorescence data on SW-13 cells suggest th at the absence of a structured network of vimentin in the mutant vim-c ells does not affect the cytoplasmic organization formed by microtubul es and acetin filaments, when compared with the wild-type vim+ cells. These studies suggest that tau associates with vimentin filaments and that these interactions may play a structural role in cells containing these filaments. (C) 1998 Academic Press.