Delayed production of arachidonic acid contributes to the delay of proteinase-activated receptor-1 (PAR1)-triggered prostaglandin E2 release in rat gastric epithelial RGM1 cells
✍ Scribed by Fumiko Sekiguchi; Ai Ohi; Yuma Maeda; Kaori Takaoka; Teruki Sekimoto; Hiroyuki Nishikawa; Prof. Atsufumi Kawabata
- Publisher
- John Wiley and Sons
- Year
- 2011
- Tongue
- English
- Weight
- 297 KB
- Volume
- 112
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
Abstract
Proteinase‐activated receptor‐1 (PAR1), upon activation, exerts prostanoid‐dependent gastroprotection, and increases prostaglandin E~2~ (PGE~2~) release through cyclooxygenase‐2 (COX‐2) upregulation in rat gastric mucosal epithelial RGM1 cells. However, there is a big time lag between the PAR1‐triggered PGE~2~ release and COX‐2 upregulation in RGM1 cells; that is, the former event takes 18 h to occur, while the latter rapidly develops and reaches a plateau in 6 h. The present study thus aimed at clarifying mechanisms for the delay of PGE~2~ release after PAR1 activation in RGM1 cells. Although a PAR1‐activating peptide, TFLLR‐NH~2~, alone caused PGE~2~ release at 18 h, but not 6 h, TFLLR‐NH~2~ in combination with arachidonic acid dramatically enhanced PGE~2~ release even for 1–6 h. TFLLR‐NH~2~ plus linoleic acid caused a similar rapid response. CP‐24879, a Δ^5^/Δ^6^‐desaturase inhibitor, abolished the PGE~2~ release induced by TFLLR‐NH~2~ plus linoleic acid, but not by TFLLR‐NH~2~ alone. The TFLLR‐NH~2~‐induced PGE~2~ release was not affected by inhibitors of cytosolic phospholipase A~2~ (cPLA~2~), Ca^2+^‐independent PLA~2~ (cPLA~2~) or secretory PLA~2~ (sPLA~2~), but was abolished by their mixture or a pan‐PLA~2~ inhibitor. Among PLA~2~ isozymes, mRNA of group IIA sPLA~2~ (sPLA~2~‐IIA) was upregulated following PAR1 stimulation for 6–18 h, whereas protein levels of PGE synthases were unchanged. These data suggest that the delay of PGE~2~ release after COX‐2 upregulation triggered by PAR1 is due to the poor supply of free arachidonic acid at the early stage in RGM1 cells, and that plural isozymes of PLA~2~ including sPLA~2~‐IIA may complementarily contribute to the liberation of free arachidonic acid. J. Cell. Biochem. 112: 909–915, 2011. © 2010 Wiley‐Liss, Inc.