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Department of Pharmacology, University of California, San Diego, La Jolla, California 92093-0636
Madin-Darby canine
kidney (MDCK) cells release ATP upon mechanical or biochemical
activation, initiating P2Y receptor signaling that regulates basal
levels of multiple second messengers, including cAMP (J Biol
Chem 275: 11735-11739, 2000). Data shown here document inhibition of cAMP formation by Gd3+ and niflumic acid,
channel inhibitors that block ATP release. cAMP production is
stimulated via Ca2+-dependent activation of cytosolic
phospholipase A2, release of arachidonic acid (AA), and
cyclooxygenase (COX)-dependent production of prostaglandins, which
activate prostanoid receptors coupled to Gs and adenylyl
cyclase. In the current investigation, we assessed the expression and
functional role of the two known isoforms of COX, COX-1 and
COX-2. Treatment of cells with either a COX-1-selective inhibitor, SC-560, or COX-2-selective inhibitors, SC-58125 or NS-398, inhibited basal and UTP-stimulated cAMP levels. COX inhibitors also decreased forskolin-stimulated cAMP formation, implying this response is in part attributable to an action of AA metabolites. These
findings imply an important role for the inducible form of COX, COX-2,
under basal conditions. Indeed, COX-2 expression was readily detectable
by immunoblot, and treatments that induce or reduce COX-2 expression in
other cells (interleukin-1
, tumor necrosis factor-
, phorbol
ester, or dexamethasone) had minimal or no effect on the levels of
COX-2 immunoreactivity. RT-PCR using isoform-specific primers detected
COX-2 mRNA. We conclude that COX-2 is constitutively expressed in
MDCK-D1 cells and participates in basal and
P2Y2-mediated signaling, implying a key role for COX-2 in
regulation of epithelial cell function.
adenosine 3',5'-cyclic monophosphate; adenosine 5'-triphosphate release; arachidonic acid; prostaglandin E2
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