CREB-dependent cyclooxygenase-2 and microsomal prostaglandin E synthase-1 expression is mediated by protein kinase C and calcium

Low Salt Delivery Triggers Autocrine Release of Prostaglandin E2 From the Aldosterone-Sensitive Distal Nephron in Familial Hyperkalemic Hypertension Mice

Aberrant activation of with-no-lysine kinase (WNK)-STE20/SPS1-related proline-alanine-rich protein kinase (SPAK) kinase signaling in the distal convoluted tubule (DCT) causes unbridled activation of the thiazide-sensitive sodium chloride cotransporter (NCC), leading to familial hyperkalemic hypertension (FHHt) in humans. Studies in FHHt mice engineered to constitutively activate SPAK specifically in the DCT (CA-SPAK mice) revealed maladaptive remodeling of the aldosterone sensitive distal nephron (ASDN), characterized by decrease in the potassium excretory channel, renal outer medullary potassium (ROMK), and epithelial sodium channel (ENaC), that contributes to the hyperkalemia. The mechanisms by which NCC activation in DCT promotes remodeling of connecting tubule (CNT) are unknown, but paracrine communication and reduced salt delivery to the ASDN have been suspected. Here, we explore the involvement of prostaglandin E2 (PGE2). We found that PGE2 and the terminal PGE2 synthase, mPGES1, are increased in kidney cortex of CA-SPAK mice, compared to control or SPAK KO mice. Hydrochlorothiazide (HCTZ) reduced PGE2 to control levels, indicating increased PGE2 synthesis is dependent on increased NCC activity. Immunolocalization studies revealed mPGES1 is selectively increased in the CNT of CA-SPAK mice, implicating low salt-delivery to ASDN as the trigger. Salt titration studies in an in vitro ASDN cell model, mouse CCD cell (mCCD-CL1), confirmed PGE2 synthesis is activated by low salt, and revealed that response is paralleled by induction of mPGES1 gene expression. Finally, inhibition of the PGE2 receptor, EP1, in CA-SPAK mice partially restored potassium homeostasis as it partially rescued ROMK protein abundance, but not ENaC. Together, these data indicate low sodium delivery to the ASDN activates PGE2 synthesis and this inhibits ROMK through autocrine activation of the EP1 receptor. These findings provide new insights into the mechanism by which activation of sodium transport in the DCT causes remodeling of the ASDN.

Is fatty acid composition of human bone marrow significant to bone health?

The bone marrow adipose tissue (BMAT) is a conserved component of the marrow microenvironment, providing storage and release of energy and stabilizing the marrow extent. Also, it is recognized both the amount and quality of BMAT are relevant to preserve the functional relationships between BMAT, bone, and blood cell production. In this article we ponder the information supporting the tenet that the quality of BMAT is relevant to bone health. In the human adult the distribution of BMAT is heterogeneous over the entire skeleton, and both BMAT accumulation and bone loss come about with aging in healthy populations. But some pathological conditions which increase BMAT formation lead to bone impairment and fragility. Analysis in vivo of the relative content of saturated and unsaturated fatty acids (FA) in BMAT indicates site-related bone marrow fat composition and an association between increased unsaturation index (UI) and bone health. With aging some impairment ensues in the regulation of bone marrow cells and systemic signals leading to local chronic inflammation. Most of the bone loss diseases which evolve altered BMAT composition have as common factors aging and/or chronic inflammation. Both saturated and unsaturated FAs originate lipid species which are active mediators in the inflammation process. Increased free saturated FAs may lead to lipotoxicity of bone marrow cells. The pro-inflammatory, anti-inflammatory or resolving actions of compounds derived from long chain poly unsaturated FAs (PUFA) on bone cells is varied, and depending on the metabolism of the parent n:3 or n:6 PUFAs series. Taking together the evidence substantiate that marrow adipocyte function is fundamental for an efficient link between systemic and marrow fatty acids to accomplish specific energy or regulatory needs of skeletal and marrow cells. Further, they reveal marrow requirements of PUFAs.

Termination mechanism of CREB-dependent activation of COX-2 expression in early phase of adipogenesis

We elucidated the molecular mechanism of prostaglandin (PG) E2- and PGF2α-mediated suppression of the early phase of adipogenesis through enhanced COX-2 expression in 3T3-L1 cells. 3-Isobutyl-1-methylxanthine, an inhibitor of phosphodiesterase which catalyzes the conversion of cAMP to AMP, enhanced the activity of protein kinase A (PKA). Dibutyryl cAMP activated PKA and enhanced the phosphorylation of cAMP response element (CRE)-binding protein (CREB). The ability of CREB binding to the CRE of the COX-2 promoter was elevated for enhancement of the expression of the COX-2 gene. CREB siRNA suppressed the expression of the COX-2 gene. Furthermore, okadaic acid, a protein phosphatase (PP) 1/2A inhibitor, suppressed the progression of adipogenesis by preventing PP1/2A-mediated suppression of CREB-dependent COX-2 expression, thus resulting in increased production of anti-adipogenic PGE2 and PGF2α. These results indicate that CREB-dependent expression of COX-2 for the production of anti-adipogenic PGs is critical for the regulation of the early phase of adipogenesis.

Modulation of Rho-Rock signaling pathway protects oligodendrocytes against cytokine toxicity via PPAR-α-dependent mechanism

We earlier documented that lovastatin (LOV)-mediated inhibition of small Rho GTPases activity protects vulnerable oligodendrocytes (OLs) in mixed glial cell cultures stimulated with Th1 cytokines and in a murine model of multiple sclerosis (MS). However, the precise mechanism of OL protection remains unclear. We here employed genetic and biochemical approaches to elucidate the underlying mechanism that protects LOV treated OLs from Th1 (tumor necrosis factor-α) and Th17 (interleukin-17) cytokines toxicity in in vitro. Cytokines enhanced the reactive oxygen species (ROS) generation and mitochondrial membrane depolarization with corresponding lowering of glutathione (reduced) level in OLs and that were reverted by LOV. In addition, the expression of ROS detoxifying enzymes (catalase and superoxide-dismutase 2) and the transactivation of peroxisome proliferators-activated receptor (PPAR)-α/-β/-γ including PPAR-γ coactivator-1α were enhanced by LOV in similarly treated OLs. Interestingly, LOV-mediated inhibition of small Rho GTPases, i.e., RhoA and cdc42, and Rho-associated kinase (ROCK) activity enhanced the levels of PPAR ligands in OLs via extracellular signal regulated kinase (1/2)/p38 mitogen-activated protein kinase/cytoplasmic phospholipase 2/cyclooxygenase-2 signaling cascade activation. Small hairpin RNA transfection-based studies established that LOV mainly enhances PPAR-α and less so of PPAR-β and PPAR-γ transactivation that enhances ROS detoxifying defense in OLs. In support of this, the observed LOV-mediated protection was lacking in PPAR-α-deficient OLs exposed to cytokines. Collectively, these data provide unprecedented evidence that LOV-mediated inhibition of the Rho-ROCK signaling pathway boosts ROS detoxifying defense in OLs via PPAR-α-dependent mechanism that has implication in neurodegenerative disorders including MS.

Cell signalling by reactive lipid species: new concepts and molecular mechanisms

The process of lipid peroxidation is widespread in biology and is mediated through both enzymatic and non-enzymatic pathways. A significant proportion of the oxidized lipid products are electrophilic in nature, the RLS (reactive lipid species), and react with cellular nucleophiles such as the amino acids cysteine, lysine and histidine. Cell signalling by electrophiles appears to be limited to the modification of cysteine residues in proteins, whereas non-specific toxic effects involve modification of other nucleophiles. RLS have been found to participate in several physiological pathways including resolution of inflammation, cell death and induction of cellular antioxidants through the modification of specific signalling proteins. The covalent modification of proteins endows some unique features to this signalling mechanism which we have termed the ‘covalent advantage’. For example, covalent modification of signalling proteins allows for the accumulation of a signal over time. The activation of cell signalling pathways by electrophiles is hierarchical and depends on a complex interaction of factors such as the intrinsic chemical reactivity of the electrophile, the intracellular domain to which it is exposed and steric factors. This introduces the concept of electrophilic signalling domains in which the production of the lipid electrophile is in close proximity to the thiol-containing signalling protein. In addition, we propose that the role of glutathione and associated enzymes is to insulate the signalling domain from uncontrolled electrophilic stress. The persistence of the signal is in turn regulated by the proteasomal pathway which may itself be subject to redox regulation by RLS. Cell death mediated by RLS is associated with bioenergetic dysfunction, and the damaged proteins are probably removed by the lysosome-autophagy pathway.

Carnosol and carnosic acids from Salvia officinalis inhibit microsomal prostaglandin E2 synthase-1

Prostaglandin E(2) (PGE(2)), the most relevant eicosanoid promoting inflammation and tumorigenesis, is formed by cyclooxygenases (COXs) and PGE(2) synthases from free arachidonic acid. Preparations of the leaves of Salvia officinalis are commonly used in folk medicine as an effective antiseptic and anti-inflammatory remedy and possess anticancer activity. Here, we demonstrate that a standard ethyl acetate extract of S. officinalis efficiently suppresses the formation of PGE(2) in a cell-free assay by direct interference with microsomal PGE(2) synthase (mPGES)-1. Bioactivity-guided fractionation of the extract yielded closely related fractions that potently suppressed mPGES-1 with IC(50) values between 1.9 and 3.5 μg/ml. Component analysis of these fractions revealed the diterpenes carnosol and carnosic acid as potential bioactive principles inhibiting mPGES-1 activity with IC(50) values of 5.0 μM. Using a human whole-blood assay as a robust cell-based model, carnosic acid, but not carnosol, blocked PGE(2) generation upon stimulation with lipopolysaccharide (IC(50) = 9.3 μM). Carnosic acid neither inhibited the concomitant biosynthesis of other prostanoids [6-keto PGF(1α), 12(S)-hydroxy-5-cis-8,10-trans-heptadecatrienoic acid, and thromboxane B(2)] in human whole blood nor affected the activities of COX-1/2 in a cell-free assay. Together, S. officinalis extracts and its ingredients carnosol and carnosic acid inhibit PGE(2) formation by selectively targeting mPGES-1. We conclude that the inhibitory effect of carnosic acid on PGE(2) formation, observed in the physiologically relevant whole-blood model, may critically contribute to the anti-inflammatory and anticarcinogenic properties of S. officinalis.

Loss of 15-hydroxyprostaglandin dehydrogenase increases prostaglandin E2 in pancreatic tumors

OBJECTIVES

Prostaglandin E2 (PGE2) is a product of cyclooxygenase (COX) and PGE synthase (PGES) and deactivated by 15-hydroxyprostaglandin dehydrogenase (PGDH). Down-regulation of PGDH contributes to PGE2 accumulation in lung and colon cancers but has not been identified in pancreatic cancer.

METHODS

Normal human pancreatic and tumor-matched tissues, as well as MiaPaCa-2 and BxPC-3 cell lines, were assessed for COX-2, microsomal PGES-1, PGDH, and snail homolog 1 (SNAI1) and SNAI2 expressions by real-time polymerase chain reaction and Western blotting and PGE2 by enzyme-linked immunosorbent assay.

RESULTS

Normal tissues exhibited low COX-2 messenger RNA (mRNA) and protein expressions and high PGDH mRNA and protein expressions and PGE2 levels at 13 pg/mg of protein. In contrast, tumor tissues exhibited high COX-2 mRNA and protein expressions and low PGDH mRNA and protein expressions and PGE2 levels at 32 pg/mg of protein. Tumor tissues exhibited significantly elevated expressions of SNAI2 mRNA and protein but not SNAI1 because SNAI1 and SNAI2 reportedly down-regulate PGDH expression. The COX-2-positive BxPC-3 but not the COX-2-negative MiaPaCa-2 treated with 100-nmol/L PGE2 induced phosphorylated extracellular signal-related kinase that was blocked by the mitogen-activated protein kinase kinase inhibitor U0126, demonstrating the ability of PGE2 to activate ERK.

CONCLUSIONS

These results suggest that enhanced PGE2 production proceeds through the expressions of COX-2 and microsomal PGES-1 and down-regulation of PGDH by SNAI2 in pancreatic tumors.

Knockdown of L calcium channel subtypes: differential effects in neuropathic pain

The maintenance of chronic pain states requires the regulation of gene expression, which relies on an influx of calcium. Calcium influx through neuronal L-type voltage-gated calcium channels (LTCs) plays a pivotal role in excitation-transcription coupling, but the involvement of LTCs in chronic pain remains unclear. We used a peptide nucleic acid (transportan 10-PNA conjugates)-based antisense strategy to investigate the role of the LTC subtypes Ca(V)1.2 and Ca(V)1.3 in long-term pain sensitization in a rat model of neuropathy (spinal nerve ligation). Our results demonstrate that specific knockdown of Ca(V)1.2 in the spinal dorsal horn reversed the neuropathy-associated mechanical hypersensitivity and the hyperexcitability and increased responsiveness of dorsal horn neurons. Intrathecal application of anti-Ca(V)1.2 siRNAs confirmed the preceding results. We also demonstrated an upregulation of Ca(V)1.2 mRNA and protein in neuropathic animals concomitant to specific Ca(V)1.2-dependent phosphorylation of the cAMP response element (CRE)-binding protein (CREB) transcription factor. Moreover, spinal nerve ligation animals showed enhanced transcription of the CREB/CRE-dependent gene COX-2 (cyclooxygenase 2), which also depends strictly on Ca(V)1.2 activation. We propose that L-type calcium channels in the spinal dorsal horn play an important role in pain processing, and that the maintenance of chronic neuropathic pain depends specifically on channels comprising Ca(V)1.2.

Proteinase-activated receptor-2-triggered prostaglandin E(2) release, but not cyclooxygenase-2 upregulation, requires activation of the phosphatidylinositol 3-kinase/Akt / nuclear factor-kappaB pathway in human alveolar epithelial cells

Proteinase-activated receptor-2 (PAR2) triggers upregulation of cyclooxygenase-2 (COX-2) and prostaglandin E(2) (PGE(2)) formation in human alveolar epithelial A549 cells. This COX-2 upregulation appears to involve the Src / epidermal growth factor (EGF) receptor / p38 MAP kinase (p38MAPK) pathway and also the cAMP-response element-binding protein (CREB) pathway. Here, we investigated the roles of nuclear factor-kappaB (NF-kappaB)-related signals in the PAR2-triggered PGE(2) release / COX-2 upregulation in A549 cells. The PAR2-triggered PGE(2) release was clearly blocked by an inhibitor of the NF-kappaB pathway. Stimulation of PAR2 actually caused phosphorylation of inhibitor-kappaB, an indicator of NF-kappaB activation, an effect being blocked by inhibitors of MEK, phosphatidylinositol 3-kinase (PI3-kinase), and Akt, but little or not by inhibitors of p38MAPK and JNK. Stimulation of PAR2 also caused phosphorylation of Akt, an effect suppressed by inhibitors of PI3-kinase and MEK. Nonetheless, the PAR2-triggered upregulation of COX-2 was resistant to inhibitors of NF-kappaB, PI3-kinase, and Akt, but was attenuated by inhibitors of MEK and JNK. Stimulation of PAR2 induced phosphorylation of CREB, an effect abolished by an inhibitor of MEK but not inhibitors of p38MAPK and EGF receptor. These findings demonstrate that the MEK / ERK / PI3-kinase / Akt / NF-kappaB pathway is involved in PAR2-triggered PGE(2) formation, but not upregulation of COX-2 that is dependent on activation of ERK/CREB and JNK in addition to p38MAPK.

Regulation of prostaglandin E2 synthase expression in activated primary rat microglia: evidence for uncoupled regulation of mPGES-1 and COX-2

Prostaglandin E2 (PGE2) is among the most important mediators involved in neuroinflammatory processes. The final step of its synthesis is regulated by enzymes termed prostaglandin E2 synthases (PGES). Three PGES are known, cytosolic (c)PGES, membrane-associated (m)PGES-1 and mPGES-2. The expression of mPGES-1 is induced by inflammatory stimuli such as lipopolysaccharide (LPS), interleukin (IL)-1beta, and tumor necrosis factor (TNF)-alpha. Although some roles of mPGES-1 have already been suggested, its function in the CNS and the signaling pathways involved in its upregulation are poorly understood. In this study, we examined the regulation of mPGES-1 in primary rat microglia and the signaling pathways involved in its expression. Whereas the expression of cPGES and mPGES-2 was not stimulated by LPS, low doses of LPS (0.1-1 ng/mL) sufficiently stimulated mPGES-1 mRNA expression. A corresponding protein synthesis, however, was obtained only with higher doses (10-100 ng/mL). The LPS-induced increase of mPGES-1 was inhibited by different signaling pathway inhibitors, such as SP600125, LY294002, GF109203X, and SC-514, suggesting the involvement of c-Jun N-terminal kinase (JNK), phosphatidylinositol 3-kinase (PI-3K)/Akt, protein kinase C (PKC) pathways, and the nuclear factor (NF)-kappaB, respectively. In contrast to other reports, LPS-induced mPGES-1 synthesis was not invariably coupled to the synthesis of COX-2, since inhibition of PI-3K with LY294002 decreased mPGES-1 but increased COX-2 levels. This detailed view of the intracellular signaling pathways involved in mPGES-1 expression in activated microglia opens a new avenue in the search for novel potential therapeutic targets to reduce neuroinflammation, and demonstrates that mPGES-1 expression is not strictly coupled to the expression of COX-2.

LY294002 inhibits glucocorticoid-induced COX-2 gene expression in cardiomyocytes through a phosphatidylinositol 3 kinase-independent mechanism

Glucocorticoids induce COX-2 expression in rat cardiomyocytes. While investigating whether phosphatidylinositol 3 kinase (PI3K) plays a role in corticosterone (CT)-induced COX-2, we found that LY294002 (LY29) but not wortmannin (WM) attenuates CT from inducing COX-2 gene expression. Expression of a dominant-negative mutant of p85 subunit of PI3K failed to inhibit CT from inducing COX-2 expression. CT did not activate PI3K/AKT signaling pathway whereas LY29 and WM decreased the activity of PI3K. LY303511 (LY30), a structural analogue and a negative control for PI3K inhibitory activity of LY29, also suppressed COX-2 induction. These data suggest PI3K-independent mechanisms in regulating CT-induced COX-2 expression. LY29 and LY30 do not inhibit glucocorticoid receptor transactivity. Both compounds have been reported to inhibit Casein Kinase 2 activity and modulate potassium and calcium levels independent of PI3K, while LY29 has been reported to inhibit mammalian Target of Rapamycin (mTOR), and DNA-dependent Protein Kinase (DNA-PK). Inhibitor of Casein Kinase 2 (CK2), mTOR or DNA-PK failed to prevent CT from inducing COX-2 expression. Tetraethylammonium (TEA), a potassium channel blocker, and nimodipine, a calcium channel blocker, both attenuated CT from inducing COX-2 gene expression. CT was found to increase intracellular Ca(2+) concentration, which can be inhibited by LY29, TEA or nimodipine. These data suggest a possible role of calcium instead of PI3K in CT-induced COX-2 expression in cardiomyocytes.

15-Hydroxyprostaglandin dehydrogenase suppresses K-RasV12-dependent tumor formation in Nu/Nu mice

Oncogenic Ras mutations are early genetic events in colorectal cancer that induce cyclooxygenase (COX)-2 expression and prostaglandin E(2) (PGE(2)) biosynthesis. PGE(2), a downstream product of COX-2, promotes cancer progression by modulating proliferation, apoptosis and angiogenesis. 15-hydroxyprostaglandin dehydrogenase (PGDH) degrades PGE(2) and is down-regulated in colorectal cancer, suggesting that PGDH plays a role in regulating PGE(2) levels and that PGDH over-expression could attenuate Ras-mediated tumorigenesis. Lentiviral transduction was used to express GFP (18.GFP), K-Ras(V12) (18.K-Ras(V12)), PGDH (18.PGDH) or both K-Ras(V12) and PGDH (18.K-Ras(V12).PGDH) in nontumorigenic rat intestinal epithelial (IEC-18) cells. 18.K-Ras(V12) cells exhibited increased phosphorylation of MAP kinases and CREB, proliferation rates, COX-2 and microsomal prostaglandin E synthase (mPGES)-1 expression and PGE(2) and PGI(2) levels. 18.PGDH and 18.K-Ras(V12).PGDH cells had 10(4)-fold increases in PGDH activity with decreased PGE(2) and PGI(2) levels, COX-2 and mPGES-1 expression and proliferation rates. 18.GFP, 18.PGDH, and 18.K-Ras(V12).PGDH cells were unable to grow in soft agar media whereas 18.K-Ras(V12) cells exhibited anchorage-independent cell growth. Xenografts of implanted 18.K-Ras(V12) cells in nu/nu mice produced rapid (2 wk) tumors with uniform antibody staining for COX-2 and mPGES-1 throughout the tumor and elevated PGE(2) levels. Xenografts of 18.K-Ras(V12).PGDH cells exhibited delayed (8 wk) tumor formation with negligible COX-2 and mPGES-1 expression and significantly decreased PGE(2) levels. 18.K-Ras(V12).PGDH tumors had decreased staining of the proliferative marker, Ki-67, and a significant increase in apoptosis in the central region of the tumor. Based on these data, we conclude that PGDH expression suppresses K-Ras(V12)-mediated tumorigenesis in intestinal epithelial cells.

Differential regulation of myometrial prostaglandin production by changes in length

OBJECTIVE

The purpose of this study was to determine whether stretching and shortening of human myometrial strips alters prostaglandin production.

STUDY DESIGN

We measured 6-keto prostaglandin F1alpha (PGF1alpha; a PGI2 metabolite) and PGF2alpha in the contraction baths of myometrial strips that were obtained at cesarean delivery from 5 term pregnant women. Fluid was collected after the stretching and after the strip lengths were decreased by 4%, 6%, or 8%. Prostaglandin concentrations were measured in triplicate by competitive enzyme immunoassay and compared by Kruskal-Wallis tests.

RESULTS

Stretching myometrial strips increased the production of 6-keto PGF1alpha by 31%, but not PGF2alpha. Shortening strips had little effect on 6-keto PGF1alpha production, but increased PGF2alpha production by 158%.

CONCLUSION

Stretching myometrial strips from pregnant women increases synthesis of PGI2; shortening strips increases synthesis of PGF2alpha. Differential prostaglandin synthesis that is related to myometrial stretching and shortening could play a role in uterine quiescence during gestation and increased contractility during parturition.

Ang II and EGF synergistically induce COX-2 expression via CREB in intestinal epithelial cells

Cyclooxygenase (COX)-2 derived prostaglandins (PGs) play a major role in intestinal inflammation and colorectal carcinogenesis. Because COX-2 is the rate-limiting step in the production of PGs, mechanisms that regulate COX-2 expression control PG production in the cell. Using the non-tumorigenic, rat intestinal epithelial cell, IEC-18, we demonstrate that co-activation of endogenously expressed AT(1) receptor and EGFR resulted in synergistic expression of COX-2 mRNA and protein involving transcriptional and post-transcriptional mechanisms. Ang II and EGF induced transient phosphorylation of ERK, p38(MAPK) and CREB. Co-stimulation with Ang II and EGF prolonged phosphorylation of ERK, p38(MAPK), and CREB. The p38(MAPK) selective inhibitor, SB202190, but not the MEK selective inhibitor, PD98059, or the EGFR kinase inhibitor, AG1478, inhibited Ang II-dependent COX-2 expression and CREB phosphorylation. EGF-dependent COX-2 expression and CREB phosphorylation were inhibited by SB202190, PD98059, and AG1478. Inhibition of CREB expression using two separate RNAi methods blocked COX-2 expression by Ang II and EGF. Expression of a dominant negative CREB mutant inhibited Ang II- and EGF-dependent induction of the COX-2 promoter. Ang II induced luciferase expression in cells transfected with the CRE-luc reporter vector and cells co-transfected with Gal4-luc reporter vector and a Gal4-CREB expression vector. Chromatin immunoprecipitation assays demonstrated CREB binding to the proximal rat COX-2 promoter region containing a CRE cis-acting element. These results indicate that co-stimulation with Ang II and EGF synergistically induced COX-2 expression in these intestinal epithelial cells through p38(MAPK) mediated signaling cascades that converge onto CREB.

Molecular signaling in necrotizing enterocolitis: regulation of intestinal COX-2 expression

Necrotizing enterocolitis (NEC) is the most common surgical emergency in premature infants. The underlying etiology of NEC remains unknown, although bacterial colonization of the gut, formula feeding, and perinatal stress have been implicated as putative risk factors. The disease is characterized by exuberant gut inflammation leading to ischemia and coagulation necrosis of the intestinal epithelium. The molecular and cellular mechanisms responsible for these pathologic changes are poorly understood. It has been shown that various exogenous and endogenous mediators such as lipopolysaccharide, inflammatory cytokines, platelet activating factor, and nitric oxide may play a role in the pathogenesis of NEC. Recent studies in our laboratory and others have established a link between NEC and activation of cyclooxygenase-2, the enzyme that catalyzes the rate-limiting step in the biosynthesis of prostanoids. The challenge is in defining the molecular signaling pathways leading to accumulation of these mediators early in the disease progression, before the onset of tissue necrosis and systemic sepsis. Identification and characterization of these pathways could lead to the development of novel treatment strategies to alleviate the morbidity and mortality associated with NEC.

Protein kinase Cδ-mediated CREB activation regulates ghrelin-induced cyclooxygenase-2 expression and prostaglandin E2 production in human colonic epithelial cells

Ghrelin, a newly identified gastric peptide, is known for its potent activity in growth hormone release and appetite. Our recent study showed that ghrelin could stimulate protein kinase C-mediated activation of nuclear factor-kappaB (NF-kappaB) and interleukin-8 secretion in human colonic epithelial cells transfected with a functional ghrelin receptor. In the present study, the effect of ghrelin stimulation on cyclooxygenese-2 expression and prostaglandin E2 production was examined. The data indicate that ghrelin significantly increased the levels of cyclooxygenase-2 (COX-2) protein as well as its promoter activity, which leaded to profound increase in prostaglandin E2 secretion. In order to examine the involvement of NF-kappaB and cAMP responsive element-binding protein (CREB) in this response, the NF-kappaB inhibitory protein IkappaBalpha or a dominant negative mutant of CREB was co-transfected into cells and the data show that transfection of either IkappaBalpha or DN-CREB significantly attenuated ghrelin-induced COX-2 expression. Moreover ghrelin stimulated phosphorylation of CREB, which was mediated primarily via protein kinase Cdelta activation. Furthermore, inhibition of PKCdelta function significantly attenuated ghrelin-induced COX-2 expression. In addition, ghrelin stimulates phosphorylation of PKCdelta. Together, these results indicate that in addition to NF-kappaB, protein kinase Cdelta-mediated CREB activation plays an important role in the cellular responses of ghrelin.