Hypertonic sodium chloride and mannitol induces COX-2 via different signaling pathways in mouse cortical collecting duct M-1 cells.
The kidney cortical collecting duct is an important site for the maintenance of sodium balance. Previous studies have shown that, in renal medullary cells, hypertonic stress induces expression of cyclooxygenase-2 (COX-2) via NF-kappaB activation, but little is known about COX-2 expression in response to hypertonicity in the cortical collecting duct. Therefore, we examined the mechanism of hypertonic induction of COX-2 in M-1 cells derived from mouse cortical collecting duct. Induction of COX-2 protein was detected within 6 h of treatment with hypertonic sodium chloride. The treatment also increased COX-2 mRNA accumulation in a cycloheximide-independent manner, suggesting that ongoing protein synthesis is not required for COX-2 induction. Using reporter plasmids containing 0.2-, 0.3-, and 1.5-kb fragments of the COX-2 promoter, we found that hypertonic induction of COX-2 was due to an increase in promoter activity. The COX-2-inductive effect of hypertonicity was inhibited by SB203580, indicating that the effect is mediated by p38 MAPK. Since p38 MAPK can activate NF-kappaB, we made point mutations in the NF-kappaB binding site within the COX-2 promoter. The mutations did not block the induction of COX-2 promoter activity by hypertonic sodium chloride, and hypertonic sodium chloride failed to activate NF-kappaB binding site-driven reporter gene constructs. In contrast, hypertonic mannitol activated NF-kappaB, indicating that hypertonic mannitol and hypertonic sodium chloride activate COX-2 by different mechanisms. Thus, induction of COX-2 expression in M-1 cells by hypertonic sodium chloride does not involve activation of NF-kappaB. Furthermore, the signal transduction pathways that respond to hypertonic stress vary for different osmolytes in cortical collecting duct cells.
Lim
WonChung
W
College of Engineering, Institute of Biotechnology, Department of Bioscience and Biotechnology, Sejong University, Seoul, South Korea.
Jung
JinSup
J
Surh
YoungJoon
Y
Inoue
Hiroyasu
H
Lee
YoungJoo
Y
D000818:Animals; D002460:Cell Line; D051546:Cyclooxygenase 2 / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000201:enzymology*; D008353:Mannitol / Q000494:pharmacology*; D051379:Mice; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D012462:Saline Solution, Hypertonic / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D012965:Sodium Chloride / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000187:drug effects / Q000378:metabolism
D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D012462:Saline Solution, Hypertonic; D051996:Transcription Factor RelA; D008353:Mannitol; D012965:Sodium Chloride; D051546:Cyclooxygenase 2