Premium
Rac1/OSM and PLC‐gamma1 contribute in combination to high NaCl‐induced activation of the osmoprotective transcription factor TonEBP/OREBP
Author(s) -
Zhou Xiaoming,
Burg Maurice B.,
Ferraris Joan D.
Publication year - 2011
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.25.1_supplement.655.8
Subject(s) - rac1 , gene knockdown , transfection , microbiology and biotechnology , chemistry , p38 mitogen activated protein kinases , phosphorylation , biology , protein kinase a , biochemistry , signal transduction , gene
Separate reports that hypertonicity activates p38 via a Rac1/OSM ‐>MEKK3 ‐>MKK3 ‐> p38pathway and that p38 contributes to activation of TonEBP/OREBP led us to hypothesize that Rac1 might activate TonEBP/OREBP via p38. The present studies examine that possibility. We find that siRNA knockdown of Rac1 or OSM reduces high NaCl‐induced increase of TonEBP transcriptional activity (by reducing transactivating activity, but not nuclear localization). siRNA knock down of MKK3 does not reduce TonEBP/OREBP transcriptional activity, but siRNA knockdown of MKK6 does. Nevertheless, the effect of Rac1 on TonEBP/OREBP is independent of MKK6 (and MKK3) since it occurs in MKK3/MKK6 null cells. Further, we find that siRNA knock down of Rac1 or OSM actually increases activity (phosphorylation) of p38 (both with and without elevation of NaCl), rather than decreasing it, as previously reported. Thus, the effect of Rac1/OSM on TonEBP/OREBP is independent of p38. It has a different explanation involving PLC‐γ1. When transfected into PLC‐γ1 null MEF cells, catalytically active Rac1 does not increase TonEBP/OREBP transcriptional activity, but it does when PLC‐γ1 is reconstituted. Similarly, dominant negative Rac1 does not inhibit TonEBP/OREBP in PLC‐γ1 null cells, unless they are reconstituted. We conclude that Rac1/OSM supports TonEBP/OREBP activity, but that this is mediated byPLC‐γ1, not p38. Supported by DIR NHLBI and USUHS