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Rac1 and p38 contribute to signaling high NaCl‐induced movement of Tonicity Enhanced Binding Protein (TonEBP) from cytoplasm to nucleus
Author(s) -
Gallardo Pedro,
Burg Maurice B,
Ferraris Joan D
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a961-d
Subject(s) - rac1 , cytosol , microbiology and biotechnology , cytoplasm , p38 mitogen activated protein kinases , nucleus , kinase , phosphorylation , signal transduction , transfection , protein kinase a , transcription factor , chemistry , biology , biochemistry , gene , enzyme
Hypertonicity activates the transcription factor TonEBP, which protects cells by stimulating the transcription of transporters and enzymes involved in organic osmolyte accumulation. p38 kinase is activated by hypertonicity and contributes to the activation of TonEBP. Rac1 GTPase signals an activation of p38 kinase, associated with hypertonicity‐induced cytoskeletal reorganization. An important part of the activation of TonEBP is its movement from cytosol to nucleus. The signaling pathways involved in this translocation are incompletely understood. Since Rac1 and p38 are activated by hypertonicity and p38 is involved in TonEBP activation, we hypothesized that Rac1 and p38 activity might both be necessary for TonEBP translocation. In the present experiments, to test for a role of Rac1we transiently transfected Hek293 cells with expression plasmids containing either catalytically active (CA) Rac1 or dominant negative (DN) Rac1 or empty vector (EV). To test for a role of p38, we added the inhibitor SB203580. The cells were incubated for 2 hours in 200 (hypotonic), 300 (normotonic) or 500 (hypertonic) mosmol/kg medium (NaCl varied). We extracted cytosolic and nuclear proteins and measured TonEBP in both fractions by Western analysis, then calculated the total amount of TonEBP in each compartment and the nuclear to cytosolic ratio (N/C). We found that at 500 mosmol/kg N/C TonEBP is increased by expression of Rac1CA and is decreased by expression of Rac1DN or by addition of SB203580. We conclude that Rac1 and p38 contribute to high NaCl‐induced movement of TonEBP from the cytoplasm to the nucleus.