Differential regulation of cyclo-oxygenase-2 and 5-lipoxygenase-activating protein (FLAP) expression by glucocorticoids in monocytic cells

Br J Pharmacol. 1997 Oct;122(4):619-24. doi: 10.1038/sj.bjp.0701425.


1. The objective of the present study was to determine the effects of dexamethasone on key constituents of prostaglandin and leukotriene biosynthesis, cyclo-oxygenase-2 (COX-2) and 5-lipoxygenase activating protein (FLAP). The human monocytic cell line THP-1 was used as a model system. mRNA and protein levels of COX-2 and FLAP were determined by Northern and Western blot analyses, respectively. 2. Low levels of COX-2 and FLAP mRNA were expressed in undifferentiated THP-1 cells, but were induced upon differentiation of the cells along the monocytic pathway by treatment with phorbol ester (TPA, 5 nM). Maximal expression was observed after two days. 3. Coincubation of the undifferentiated cells with dexamethasone (10(-9) - 10(-6) M) and phorbol ester prevented induction of COX-2 mRNA, but did not affect the induction of FLAP mRNA. 4. Dexamethasone downregulated COX-2 mRNA and protein in differentiated, monocyte-like THP-1 cells. In contrast, FLAP mRNA and protein were upregulated by dexamethasone in differentiated THP-1 cells. After 24 h, FLAP mRNA levels were increased more than 2 fold. Dexamethasone did not change 5-lipoxygenase mRNA expression. 5. Release of prostaglandin E2 (PGE2) and peptidoleukotrienes was determined in cell culture supernatants of differentiated THP-1 cells by ELISA. Calcium ionophore-dependent PGE2 synthesis was associated with COX-2 expression, whereas COX-1 and COX-2 seemed to participate in arachidonic acid-dependent PGE2 synthesis. Very low levels of peptidoleukotrienes were released from differentiated THP-1 cells upon incubation with ionophore. Treatment with dexamethasone did not significantly affect leukotriene release. 6. These data provide evidence that prostaglandin synthesis is consistently downregulated by glucocorticoids. However, the glucocorticoid-mediated induction of FLAP may provide a mechanism to maintain leukotriene biosynthesis through more efficient transfer of arachidonic acid to the 5-lipoxygenase reaction, in spite of inhibitory effects on other enzymes of the biosynthetic pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5-Lipoxygenase-Activating Proteins
  • Arachidonate 5-Lipoxygenase / genetics
  • Arachidonate 5-Lipoxygenase / metabolism
  • Carrier Proteins / genetics*
  • Cell Differentiation / genetics
  • Cell Line
  • Cyclooxygenase 2
  • Dexamethasone / pharmacology*
  • Eicosanoids / metabolism
  • Gene Expression Regulation, Enzymologic / drug effects*
  • Humans
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Membrane Proteins / genetics*
  • Monocytes / drug effects*
  • Monocytes / metabolism
  • Prostaglandin-Endoperoxide Synthases / genetics
  • Prostaglandin-Endoperoxide Synthases / metabolism
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism


  • 5-Lipoxygenase-Activating Proteins
  • ALOX5AP protein, human
  • Carrier Proteins
  • Eicosanoids
  • Isoenzymes
  • Membrane Proteins
  • RNA, Messenger
  • Dexamethasone
  • Arachidonate 5-Lipoxygenase
  • Cyclooxygenase 2
  • PTGS2 protein, human
  • Prostaglandin-Endoperoxide Synthases