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Expression of α 1 ‐chimaerin ( rac ‐1 GAP) alters the cytoskeletal and adhesive properties of fibroblasts
Author(s) -
Herrera Roman,
Shivers Brenda D.
Publication year - 1994
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240560419
Subject(s) - microbiology and biotechnology , vinculin , stress fiber , cytoskeleton , gtpase activating protein , membrane ruffling , actin , focal adhesion , cdc42 , gtpase , rac gtp binding proteins , biology , signal transduction , chemistry , rac1 , g protein , cell , biochemistry
The small GTP‐binding protein rac ‐1, a member of the ras gene superfamily of GTPases, is thought to be a key component of a signal transduction pathway that mediates cell membrane ruffling and actin stress fiber formation induced by growth factors. rac ‐1 protein is regulated by the interplay of several activities:proteins that enhance GDP dissociation (GDP Dissociation Stimulator, GDS), inhibit nucleotide exchange (GDP Dissociation Inhibitor, GDI), or accelerate GTP hydrolysis (GTPase Activating Protein, GAP). We have assessed the relative contribution of the rac ‐1/GAP interactions to the overall activity of rac ‐1 by expressing α 1 ‐chimaerin, a rac ‐1‐specific GAP, in fibroblasts. NIH 3T3 cells were transfected with (α 1 )‐chimaerin‐expressing cells showed rac ‐1 GAP activity that was regulated by phosphatidylserine and phorbol ester. The cells expressing α 1 ‐chimaerin showed a distinct phenotype. They had altered adhesive properties as measured by their ability to bind to a fibronection‐coated glass surface, suggesting that the expression of a rac ‐1 GAP alters the assembly of integrin receptors, actin and cytoskeletal proteins such as vinculin and talin. Direct demonstration of this phenomenon was achieved by studying the organization of actin stress fiber and formation of focal adhesions in the α 1 ‐chimaerin expressing cells following stimulation by growth factors. Mock transfected cells, upon serum or lysophospatidic acid stimulation, organize actin as a dense array of parallel fibers running the length of the cell. This process did not take place in the cells expressing rac ‐1 GAP. Similarly, the formation of focal adhesions as measured by the appearance of vinculin clusters was imparied in the α 1 ‐chimaerin expressing cells. These results demonstrate that expression of a GAP for rac ‐1 in fibroblasts produces profound changes in the cytoskeletal organization and suggest that GAP activity negatively regulates rac ‐1 function.