期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2011
卷号：108
期号：29
页码：12155-12160
DOI：10.1073/pnas.1108107108
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Separate reports that hypertonicity activates p38 via a Rac1-OSM-MEKK3-MKK3-p38 pathway and that p38 contributes to activation of TonEBP/OREBP led us to the hypothesis that Rac1 might activate TonEBP/OREBP via p38. The present studies examine that possibility. High NaCl is hypertonic. We find that siRNA knockdown of Rac1 reduces high NaCl-induced increase of TonEBP/OREBP transcriptional activity (by reducing its transactivating activity but not its nuclear localization). Similarly, siRNA knockdown of osmosensing scaffold for MEKK3 (OSM) also reduces high NaCl-dependent TonEBP/OREBP transcriptional and transactivating activities. Simultaneous siRNA knockdown of Rac1 and OSM is not additive in reduction of TonEBP/OREBP transcriptional activity, indicating a common pathway. However, siRNA knockdown of MKK3 does not reduce TonEBP/OREBP transcriptional activity, although siRNA knockdown of MKK6 does. Nevertheless, the effect of Rac1 on TonEBP/OREBP is also independent of MKK6 because it occurs in MKK6-null cells. Furthermore, we find that siRNA knockdown of Rac1 or OSM actually increases activity (phosphorylation) of p38, rather than decreasing it, as previously reported. Thus, the effect of Rac1 on TonEBP/OREBP is independent of p38. We find instead that phospholipase C-{gamma}1 (PLC-{gamma}1) is involved. When transfected into PLC-{gamma}1-null mouse embryonic fibroblast cells, catalytically active Rac1 does not increase TonEBP/OREBP transcriptional activity unless PLC-{gamma}1 is reconstituted. Similarly, dominant-negative Rac1 also does not inhibit TonEBP/OREBP in PLC-{gamma}1-null cells unless PLC-{gamma}1 is reconstituted. We conclude that Rac1/OSM supports TonEBP/OREBP activity and that this activity is mediated via PLC-{gamma}1, not p38.
