eicosanoids synthesis step by step
Eicosanoids

Author: daniele viarisio
Date: 20/11/2007

Description

positive regulation negative regulation principal cell/tissue of expression

Phospholipase A2, the first enzyme in eicosanoids sinthesys

Increased calcium concentration promotes the translocation to the plasma membrane, where can colocalizes with enzymes like Cox, Lox, MAPK.

Phosphorilation on Ser505 by MAPKs

Phosphorilation on Ser515 by Ca++/calmodulin-dependent protein kinase II (CaMKII)

Phosphorilation on Ser707 by MAPK-interacting kinase (Mnk1)

Binding with PiP2 and PiP3

Binding with Vimentin, PLIP, p11

Binding with Annexin I (some annexins are upregulated by antiinflammatory glucocorticoids)

Cleaved and inactivated by Caspase-3 and -8

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COX-1 and COX-2
Two enzymes are necessary probably because their products have distinct metabolic pathways, different localization in the cell and so different effects on the cell. Some evidences suggest that PGHS-1 products act on membrane receptors, while PGHS-2 products might act more directly on nuclear receptors.

COX-1
“Constitutively” synthesized, but preferentially expressed at high levels in endothelium, monocytes, platelets, renal collecting tubules, and seminal vesicles and in cells that undergo differentiation

Sp1 regulatory elements in the promoter

Some hormonal stimuli (e.g. estrogen)

Works only with higher arachidonate concentration, >10 micromolar (exogenous source, or released during acute inflammation)

"Classical" NSAIDs (e.g. aspirin)

COX-2
Relatively more concentrated within the nuclear envelop (do the products directly act on nuclear receptors?)
Appears to couple preferentially to PGE synthase and PGI synthase

Inducible synthesis (depending of tissue of interest. E.g. synoviocytes, endothelial cells, chondrocytes, osteoblasts, monocytes/macrophages, some types of tumors)

infection, inflammation (IL-1, TNF-alpha, LPS, TPA – via NF-kB or C/EBP) mechanical stress, hypotonicity, hyperpolarization in nerve cells, growth factor

NF-kB, Sp1, ATF/CRE, E-Box, TATA Box elements in the promoter

Works with low arachidonate concentrations, <1 micromolar (endogenous source)

glucocorticoid, anti-inflammatory cytokines (IL-4, IL-6, IL-10...)

COX-2 specific NSAIDs (celecoxib, rofecoxib, valdecoxib, parecoxib)

There are two types of PGD synthase: H-PGDS and L-PGDS
PGD2 is known as a potent endogenous somnogen, nociceptive modulator, anti-coagulant, vasodilator, bronchoconstrictor, and also as an allergic and inflammatory mediator released from mast cells. It has also immunossupressive properties.

H-PGDS
Glutathione-dependent, is a 26 kDa cytosolic protein, responsible for the biosynthesis of PGD2 in immune and inflammatory cells such as mast cells, antigen-presenting cells, and Th2 cells. It is also preent in fallopian tube, endometrial gland cells, extravillous trophoblasts, and villous trophoblasts, and perhaps plays animportant role in female reproduction

Ca++ and Mg++ dependent

OCT-1, AP-2 elements in the promoter

RasGRP4 (acting downstream of stem cell factor/c-kit receptor) may act as a common upstream regulator in mast cells

L-PGDS

Glutathione-independent (but needs other sulphydryl compounds), is a 26 kDa secretory protein, N-glycosylated dual functional monomeric protein which acts as a PGD2- producing enzyme, as well as a lipophilic ligand-binding protein. L-PGDS is present in cerebrospinal fluid, seminal plasma and may play an important role in male reproduction

Prostacyclin , also known as prostaglandin I2, is a potent vasodilator and inhibitor of platelet aggregation

PGIS is constitutively expressed in vascular cells such as in endothelial cells and smooth muscle cells, as well in some non-vascular cells, including neurons. Colocalizes with COX-1 in resting endothelial cells and with COX-2 (in the nuclear envelope and in the ER) in EC stimulated by PMA. In EC is less expressed than PGES, but when PGIS is upregulated PGH2 seems to be converted more easily to PGI. Some evidences show that intracellular PGI2 could directly activates PPARgamma

Promoter TATA less but with two Sp1 binding region. A polymorphism in Sp1 region is related with hypertension

IL-6

PGIS (such as PLA2 and COX-2) is overexpressed in RAS transfected cells, suggesting a role for the RAS signaling pathway

weakly by IL-1beta

weakly by TNF-alpha

Superoxide ion and NO (via formation of peroxynitrite and succesive nitration of Tyr-430 that completely inhibits the activity)

LPS (via NO production). PGIS inhibition in endothelial cells with LPS results in a shunt to PGE2 synthesis!

Three isoforms of PGE synthase have been described:
membrane prostaglandin E synthase 1 (mPGES-1) 14-15 kDa, GSH-dependent
membrane prostaglandin E synthase 2 (mPGES-2) 33 kDa GSH-independent
cytosolic prostaglandin E synthase (cPGES) 26 kDa GSH-dependent

mPGES-1: prostate, testis, placenta, mammary gland, bladder, some kind of tumors (pulmonary fibroblast, cervical epithelial cells), synovial macrophages and fibroblast in rheumatoid arthritis, cartilage in osteoarthristis. Preferentially couples with COX-2.

IL-1beta, via ERK (MAPK family)

NF-kB, via EGR-1 that binds GC-reach sequences in the promoter

PPARgamma, via inhibition of EGR-1 expression

15d-PGJ2 (anti-inflammatory effect), via NF-kB inhibition and PPARgamma stimulation

mPGES-2: brain, heart, skeletal muscle, kidney, liver. Modest preference for coordination with COX-2

cPGES: ubiquitous. Preferentially couples with COX-1.

GSH

LPS

Some pro-inflammatory cytokines could affect not direclty the activity but the localization to the nuclear membrane, leading to an increased association with COX

(in vitro) HSP90

phosphorylation by casein kinase II (CK-II), a client protein for HSP90

Dexamethasone

p38MAPK inhibitors (probably inhibiting CK-II activity)

Prostaglandin (PG) F2 is synthesized via three pathways from PGE2, PGD2, or PGH2 by PGE 9-ketoreductase, PGD 11-ketoreductase, or PGH 9-, 11-endoperoxide reductase, respectively.

PGE 9-ketoreductase is demonstrated to be very important in PGs production in endometrium during periimplantation period

NADPH dependent

There are two isozymes of PGD 11-ketoreductase, one in the lung (contractile interstitial cells) and the other in the liver (sinusoidal endothelial cells, in coexpression with COX-1) with different Km values for PGD2 (120 and 10microM, respectively). mRNA has been also found in kidney, muscle and peripheral blood lymphocytes.

NADPH dependent

phenanthrenequinone

9-,11-endoperoxide reductase is an isozyme of glutathione S-transferase and has been isolated from seminal vescicle

NADPH and GSH dependent

Hematopoietic cells, such as platelets, macrophages, monocytes and leukocytes, as well as in various tissues, particularly in lung, kidney, liver, spleen, prostate, placenta and thymus. It seems that TXA2 can act in a paracrine manner to induce endothelial COX-2 expression and PGI2 synthesis.

The promoter contains two putative elements, a TATA box, an initiator and a cis-element for NF-E2 transcription factor binding at−83/−77.

Transcription factor NF-E2 is a basic leucine zipper heterodimer consisting of p45 and p18 subunits. Expression of p45 is primarily restricted to hematopoietic cells, while small Maf (p18) appears to be ubiquitously expressed

Further studies have indicated that TXAS is coordinately expressed with other platelet proteins, such as GPIIb (CD41) and c-mpl, during megakaryocyte differentiation but is not directly involved in platelet formation.

PPARg

Pathways
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