Different roles of cAMP/PKA and PKC signaling in regulating progesterone and PGE levels in immortalized rat granulosa cell cultures.

Follicular cells from various species secrete steroids and prostaglandins, which are crucial for reproduction, in response to gonadotropins. Here, we examined prostaglandin E (PGE) secretion from immortalized rat granulosa cells derived from preovulaotry follicles expressing the rat follicle stimulating hormone receptor (denoted as FSHR cells) that produce progesterone in response to gonadotropins. The cells were stimulated with a) pregnant mare's serum gonadotropin (PMSG; a rat FSH receptor agonist), b) activators of the protein kinase A (PKA) pathway (forskolin and a cell permeable cAMP analog Dibutyryl-cAMP (DB-cAMP)) and c) protein kinase C (PKC) (12-O-tetradecanoylphorbol 13-acetate; TPA), alone and in combination for 24 h.

Celecoxib interferes to a limited extent with aspirin-mediated inhibition of platelets aggregation.

Aims: The aim of the study was to analyze the interaction between celecoxib and low dose aspirin for COX-1 binding and its consequences on the aspirin-mediated antiplatelet effects.

Methods: We investigated ex vivo the interaction between celecoxib and aspirin for COX-1 binding and measured the resulting antiplatelet effects. We applied mechanism-based pharmacokinetic-pharmacodynamic (PKPD) modelling to analyze these data and to predict in vivo platelet aggregation for different doses and administration schedules of aspirin and celecoxib.

Competition between low-dose aspirin and other NSAIDs for COX-1 binding and its clinical consequences for the drugs' antiplatelet effects.

Introduction: NSAIDs are frequently used in modern medicine to inhibit the COX enzymes and induce analgesic, antipyretic, anti-inflammatory, and antiplatelet effects. Concomitant treatment with two or more NSAIDs can lead to their competition for binding and inhibition of the COX enzymes and altered time course of the pharmacological effects.

Areas Covered: The competition between the low-dose aspirin and other NSAIDs for binding to COX-1 is described, including the recent findings on the differences in the interaction of NSAIDs with the individual COX-1 subunits, and the clinical consequences of this drug-drug interaction.

Prostaglandin receptor EP₁-mediated differential degradation of cyclooxygenases involves a specific lysine residue.

The cyclooxygenase (COX) enzyme isoforms COX-1 and COX-2 catalyze the main step in the generation of prostanoids that mediate major physiological functions. Whereas COX-1 is a ubiquitously expressed stable protein, COX-2 is transiently upregulated in many pathologies and is often associated with a poor prognostic outcome. We have recently shown that an interaction of COX-2 with the prostaglandin EP₁ receptor accelerates its degradation via a mechanism that augments its level of ubiquitination.

Prostaglandin EP1 receptor down-regulates expression of cyclooxygenase-2 by facilitating its proteasomal degradation.

The enzyme cyclooxygenase-2 (COX-2) is rapidly and transiently up-regulated by a large variety of signals and implicated in pathologies such as inflammation and tumorigenesis. Although many signals cause COX-2 up-regulation, much less is known about mechanisms that actively down-regulate its expression. Here we show that the G protein-coupled receptor prostaglandin E(1) (EP(1)) reduces the expression of COX-2 in a concentration-dependent manner through a mechanism that does not require receptor activation.

Coxibs interfere with the action of aspirin by binding tightly to one monomer of cyclooxygenase-1.

Pain associated with inflammation involves prostaglandins synthesized from arachidonic acid (AA) through cyclooxygenase-2 (COX-2) pathways while thromboxane A(2) formed by platelets from AA via cyclooxygenase-1 (COX-1) mediates thrombosis. COX-1 and COX-2 are both targets of nonselective nonsteroidal antiinflammatory drugs (nsNSAIDs) including aspirin whereas COX-2 activity is preferentially blocked by COX-2 inhibitors called coxibs. COXs are homodimers composed of identical subunits, but we have shown that only one subunit is active at a time during catalysis; moreover, many nsNSAIDS bind to a single subunit of a COX dimer to inhibit the COX activity of the entire dimer.

Interaction between prostaglandin E2 and l-cis-diltiazem, a specific blocker of cyclic nucleotide gated channels in bovine aortic endothelial cells.

Prostaglandins are known to transduce their signals via 7 transmembrane prostanoid receptors, which typically signal through coupling to G proteins and downstream second messenger molecules and protein kinase activation. Recently we have shown that cyclic nucleotides affect prostaglandins binding to bovine aortic endothelial cells independent of protein kinases. Here we show that incubation of bovine aortic endothelial cells with permeable analogs of cAMP or cGMP leads to a rapid and reversible reduction in PGE(2) binding to the cells.

Partnering between monomers of cyclooxygenase-2 homodimers.

Prostaglandin endoperoxide H synthases (PGHSs) 1 and 2 convert arachidonic acid to prostaglandin H2 in the committed step of prostanoid biosynthesis. These enzymes are pharmacological targets of nonsteroidal antiinflammatory drugs and cyclooxygenase (COX) 2 inhibitors. Although PGHSs function as homodimers and each monomer has its own COX and peroxidase active sites, the question of whether there is cross-talk between monomers has remained unresolved.

On the interaction of specific prostaglandin H synthase-2 inhibitors with prostaglandin H synthase-1.

Previous studies with both intact cells and ram seminal vesicles microsomes have shown that the specific PGHS-2 inhibitors NS-398 (N-[2-(cyclohexyloxy)-4-nitrophenyl]methanesulfonamide) and DuP-697 (5-bromo-2[4-fluorophenyl]-3-[4-methylsulfonylphenyl]-thiophene) attenuate the inhibition of PGHS-1 caused by aspirin and indomethacin. This effect occurs at concentrations of PGHS-2 inhibitors that do not inhibit the cyclooxygenase activity of PGHS-1. Here we study the effect of NS-398 and ibuprofen, a nonspecific inhibitor, on the indomethacin-induced inhibition of purified PGHS-1 and compare this effect with that observed with microsomal enzyme.

Channel modulators affect PGE(2) binding to bovine aortic endothelial cells.

PGE(2), PGF(2alpha) and the thromboxane agonist U-46619 bind to bovine aortic endothelial cells and compete on the same binding site with similar affinity. In addition, binding remains unaffected by prolonged exposure to the ligand. These characteristics differ significantly from those of any known G-coupled prostaglandin receptor.