Levels and localization of group II phospholipase A2 and annexin I in interleukin- and dexamethasone-treated rat mesangial cells: evidence against annexin mediation of the dexamethasone-induced inhibition of group II phospholipases A2

Renal Expression of Annexin A1 Is Associated With the Severity of Renal Injury in Antineutrophil Cytoplasmic Autoantibody-Associated Vasculitis

Background

Increasing studies demonstrated the importance of activation of neutrophils in the pathogenesis of antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV). Previous studies showed that annexin A1 (ANXA1) inhibited the recruitment, transendothelial migration and respiratory burst of neutrophils and induced apoptosis of neutrophils. The current study aimed to investigate the plasma and renal levels of ANXA1 as well as their association with the disease severity in AAV patients.

Methods

Thirty-one AAV patients in active stage and 35 AAV patients in remission stage were recruited. The expression of ANXA1 in renal specimens was assessed by immunohistochemistry. The co-localization of ANXA1 with renal intrinsic and infiltrating cells was detected by double immunofluorescence. The plasma levels of ANXA1 were determined by ELISA. The association of plasma and renal levels of ANXA1 with clinicopathological parameters was further analyzed.

Results

Plasma levels of ANXA1 were significantly higher in active AAV patients than those in AAV patients in remission as well as healthy controls. The renal expression of ANXA1 was significantly higher in active AAV patients than in healthy controls and disease controls. Double immunofluorescence assay showed that ANXA1 was expressed in glomerular endothelial cells, mesangial cells, podocytes, proximal tubular epithelial cells, neutrophils, monocytes/macrophages and T cells in AAV patients. The mean optical density of ANXA1 in glomeruli was correlated with serum creatinine levels (r = −0.491, P = 0.005) and eGFR (r = 0.492, P = 0.005) at renal biopsy and the proportion of crescents (r = −0.423, P = 0.018) in renal specimens of AAV patients. The expression of ANXA1 in glomeruli of AAV patients achieving complete renal recovery was significantly higher than those achieving partial renal recovery.

Conclusion

In AAV patients, the renal expression of ANXA1 was associated with the severity of renal injury.

Therapeutic Potential of Annexin A1 Modulation in Kidney and Cardiovascular Disorders

Renal and cardiovascular disorders are very prevalent and associated with significant morbidity and mortality. Among diverse pathogenic mechanisms, the dysregulation of immune and inflammatory responses plays an essential role in such disorders. Consequently, the discovery of Annexin A1, as a glucocorticoid-inducible anti-inflammatory protein, has fueled investigation of its role in renal and cardiovascular pathologies. Indeed, with respect to the kidney, its role has been examined in diverse renal pathologies, including acute kidney injury, diabetic nephropathy, immune-mediated nephropathy, drug-induced kidney injury, kidney stone formation, and renal cancer. Regarding the cardiovascular system, major areas of investigation include the role of Annexin A1 in vascular abnormalities, atherosclerosis, and myocardial infarction. Thus, this review briefly describes major structural and functional features of Annexin A1 followed by a review of its role in pathologies of the kidney and the cardiovascular system, as well as the therapeutic potential of its modulation for such disorders.

Anaphylactic shock with methylprednisolone, Kounis syndrome and hypersensitivity to corticosteroids: a clinical paradox

Corticosteroids are widely used for the treatment of allergic reactions but paradoxically themselves may induce acute, delayed, local or systemic allergic reactions and even anaphylaxis with Kounis syndrome. They can suppress the release of arachidonic acid from mast cell membranes, via phospholipase A2 and eicosanoid biosynthesis inhibition. Corticosteroids can promote cell apoptosis and mediate in annexin or lipocortin synthesis, substances that modulate inflammatory cell activation, adhesion molecule expression, transmigratory and phagocytic functions. Antigen-antibody reaction, hapten formation, and medication contaminants are some of the incriminated causes. Patients with atopic diathesis are particularly vulnerable. Complete and thorough previous history of drug reactions or allergies is necessary before administration of any particular medication including corticosteroids.

Exploiting the Annexin A1 pathway for the development of novel anti-inflammatory therapeutics

The appreciation that the inflammatory reaction does not 'spontaneously' finish, but rather that inflammatory resolution is an active phenomenon brought about by endogenous anti-inflammatory agonists opens multiple opportunities for a reassessment of the complexity of inflammation and its main mediators. This review dwells on one of these pathways, the one centred around the glucocorticoid-regulated protein Annexin A1 and its G protein-coupled receptor. In recent years, much of the knowledge detailing the processes by which Annexin A1 expresses its anti-inflammatory role on innate immunity has been produced. Moreover, the generation of the Annexin A1 null mouse colony has provided important proof-of-concept experiments demonstrating the inhibitory properties of this mediator in the context of inflammatory and/or tissue-injury models. Therefore, Annexin A1 acts as a pivotal homeostatic mediator, where if absent, inflammation would overshoot and be prolonged. This new understanding scientific information could guide us onto the exploitation of the biological properties of Annexin A1 and its receptor to instigate novel drug discovery programmes for anti-inflammatory therapeutics. This line of research relies on the assumption that anti-inflammatory drugs designed upon endogenous anti-inflammatory mediators would be burdened by a lower degree of secondary effects as these agonists would be mimicking specific pathways activated in our body for safe disposal of inflammation. We believe that the next few years will produce examples of such new drugs and the validity of this speculation could then be assessed.

Henk van den Bosch: chemist and biochemist

Henk van den Bosch is a native of The Netherlands and recently retired from his position as Professor at Utrecht University. This article summarizes the many scientific achievements of Dr. van den Bosch. He enjoys an international reputation for his research on phospholipases A, cardiolipin biosynthesis in eukaryotes, lysophospholipases, phosphatidylcholine biosynthesis for lung surfactant, plasmalogen biosynthesis in peroxisomes, diagnosis of peroxisomal disorders and most recently his work on alkyl-dihydroxyacetone phosphate synthase. During his research career Henk van den Bosch published approximately 280 articles and presented 110 invited lectures.

Translocation of annexin I from cellular membrane to the nuclear membrane in human esophageal squamous cell carcinoma

AIM: To investigate the alteration of the annexin I subcellular localization in esophageal squamous cell carcinoma (ESCC) and the correlation between the translocation and the tumorigenesis of ESCC.

METHODS: The protein localization of annexin I was detected in both human ESCC tissues and cell line via the indirect immunofluorescence strategy.

RESULTS: In the normal esophageal epithelia the annexin I was mainly located on the plasma membrane and formed a consecutive typical trammels net. Annexin I protein also expressed dispersively in cytoplasm and the nuclei without specific localization on the nuclear membrane. In esophageal cancer annexin I decreased very sharply with scattered disappearance on the cellular membrane, however it translocated and highly expressed on the nuclear membrane, which was never found in normal esophageal epithelia. In cultured esophageal cancer cell line annexin I protein was also focused on the nuclear membrane, which was consistent with the result from esophageal cancer tissues.

CONCLUSION: This observation suggests that the translocation of annexin I protein in ESCC may correlate with the tumorigenesis of the esophageal cancer.

Group IIA and group V secretory phospholipase A(2): quantitative analysis of expression and secretion and determination of the localization and routing in rat mesangial cells

Mesangial cells can be induced to express group IIA and group V secretory phospholipase A(2) (sPLA(2)) at the mRNA level and at the protein level. In this report we quantitatively analyze the expression of both proteins in stimulated cells by Western blot techniques. We found that 75-80% of the total amount of synthesized group IIA sPLA(2) was secreted. The synthesized group V sPLA(2), however, was present almost exclusively intracellularly. The amount of group V present in the cell was comparable to the intracellular amount of group IIA sPLA(2). We furthermore studied the localization and routing of both proteins. Using fusion proteins of the group IIA or group V pre-sPLA(2) with green fluorescent protein it was established that both presequences are able to direct the proteins to the Golgi system. In immunofluorescence studies group V sPLA(2) expressed by rat mesangial cells was located in a punctate pattern in the cytosol with an enrichment near the nucleus. Immunofluorescent confocal laser scanning microscopy revealed that the group V and IIA sPLA(2) show partial colocalization in a Golgi-like structure in the inner part in the cell, but no colocalization was seen in the vesicles in the cytoplasm. The images also showed that group IIA sPLA(2) was located throughout the cell while group V was mainly present in the inner part of the cell. After treatment of the cells with brefeldin A or monensin the group IIA enzyme could no longer be detected, while group V sPLA(2) was still present although its localization was somewhat dependent on the treatment. Collectively, these results indicate that the two enzymes differ in both localization and routing in the cell, which underscores the hypothesis that the enzymes might have different functions.

Characterization of group X phospholipase A(2) as the major enzyme secreted by human keratinocytes and its regulation by the phorbol ester TPA

HaCaT as well as human primary keratinocytes constitutively expressed mRNA of the human secreted phospholipase A(2) subtype groups X, V, IIA, and IID. A similar expression pattern was also found in human skin biopsies. Protein analysis showed that under serum-free conditions only group X secreted phospholipase A(2) is secreted into cell culture supernatants of HaCaT as well as human primary keratinocytes, whereas the other secreted phospholipases A(2) were not detectable at protein level. HaCaT keratinocytes constitutively released secreted phospholipase A(2) activity into the cell culture supernatant, being reflected by a constant release of fatty acids. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate, which is a potent inducer of inflammation in skin, drastically reduced the mRNA level of group X secreted phospholipase A(2) and other secreted phospholipase A(2) subtypes as well as secreted phospholipase A(2) activity in cell culture supernatants. This suggests that inhibition of secreted phospholipase A(2) expression and activity as well as of fatty acid release by 12-O-tetradecanoylphorbol-13-acetate treatment might be a critical step impairing the integrity of the epidermis during phorbol-ester-induced pathologic processes in skin. The results show that group X secreted phospholipase A(2) represents the major secreted phospholipase A(2) subtype in human keratinocytes and thus may indicate a physiologic role for this enzyme in epidermis in vivo.

Regulation of the expression of group IIA and group V secretory phospholipases A(2) in rat mesangial cells

Rat mesangial cells synthesize and secrete a secretory phospholipase A(2) upon stimulation of the cells with cytokines, like IL-1beta and TNF and with cAMP elevating agents like forskolin. This enzyme was previously characterized to belong to group IIA sPLA(2). The discovery of several other low molecular weight phospholipases, like group IIC in murine testis and group V in human and rat heart, prompted investigations on the presence of group IIC and group V sPLA(2) in rat mesangial cells. This was done by isolating the RNA from stimulated cells and performing RT-PCR, using primers specific for group IIC and V sPLA(2). The results indicate that rat mesangial cells upon stimulation express next to group IIA also group V sPLA(2). No indications were obtained for the expression of group IIC sPLA(2). The regulation of the expression of group V sPLA(2) at the mRNA level was further investigated by examining the time-dependent expression, the influence of dexamethasone and the signaling route of the IL-1beta stimulation. The results show that the IL-1beta induced expression of group V sPLA(2) mRNA was time dependent and, similar to that of group IIA sPLA(2) mRNA, involves activation of NF-kappaB. However, in contrast to the group IIA sPLA(2), the expression of group V sPLA(2) was not influenced by the presence of dexamethasone. The expression of both phospholipases was also examined at the protein level in stimulated mesangial cells. Western blot analysis shows that stimulated mesangial cells synthesize both group IIA and group V sPLA(2) protein but the expression of group V is lower compared to that of group IIA sPLA(2). In addition, the extent of secretion into the medium appears to be considerably higher for group IIA than for group V sPLA(2).

Phospholipase A2 enzymes in eicosanoid generation

Phospholipase A2 (PLA2) enzymes cleave esterified fatty acids from membrane glycerophospholipids. The 20-carbon polyunsaturated fatty acid, arachidonic acid, is used as substrate by intermediate enzymes for the generation of eicosanoids, including leukotrienes and prostanoid products. An expanding number of PLA2 enzymes has now been identified that may participate in arachidonic acid release and thus serve a rate-limiting role in eicosanoid biosynthesis. Cellular PLA2 function for various members is regulated by constitutive or elicited expression, as well as by posttranslational events such as phosphorylation. In addition, the function of some cellular PLA2 enzymes is regulated by a requirement for calcium or by localization to a particular subcellular compartment. Finally, some PLA2 enzymes are secreted from the cell where they may directly interact with plasma membrane or transmembrane receptors to function as autocrine or paracrine mediators. Evaluating the roles of a number of these functionally similar PLA2 enzymes in the biosynthesis of leukotrienes and other eicosanoids is the focus of this review.

Dexamethasone alters arachidonate release from human epithelial cells by induction of p11 protein synthesis and inhibition of phospholipase A2 activity

The effect of the glucocorticosteroid, dexamethasone, on arachidonic acid (AA) release and on protein levels of p11 and cytosolic phospholipase A2 (cPLA2) was studied in two epithelial cell lines, HeLa cells and BEAS-2B cells. Dexamethasone treatment of HeLa cells and BEAS-2B cells increased cellular p11 protein and mRNA levels in a time- and dose-dependent manner. It had little effect on levels of cPLA2 protein. In order to determine if increased p11 protein expression resulted in increased interaction between p11 and cPLA2, anti-cPLA2 antibodies were used to immunoprecipitate p11.cPLA2 complexes and Western blots of the immunoprecipitate were used to detect p11. In cells treated with dexamethasone, more p11 was detected in the anti-cPLA2 immunoprecipitate compared with control cells. Dexamethasone treatment of HeLa cells prelabeled with [3H]AA decreased the release of [3H]AA under basal conditions and after stimulation with the calcium ionophore A23187 (10(-6) M). In order to determine if altering the p11 protein levels in HeLa cells independent of glucocorticosteroid treatment could also produce an effect on [3H]AA release, cells were stably transfected with plasmids expressing either p11 antisense mRNA or p11 mRNA. Cloned HeLa cells expressing p11 antisense mRNA exhibited less cellular p11 protein compared with control cells and greater [3H]AA release compared with cells transfected with a control vector. Cloned HeLa cells stably transfected with a p11 expression vector exhibited increased p11 cellular protein and diminished [3H]AA release under basal conditions and in response to A23187. Therefore, dexamethasone alteration of epithelial cell AA release may be due in part to induction of p11 protein expression.

Gene expression of group II phospholipase A2 in intestine in Crohn's disease

OBJECTIVE

Phospholipase A2 (PLA2) has been suggested to play an important role in the pathogenesis of inflammatory bowel diseases. Our aim was to identify cells that express group II phospholipase A2 (PLA2-II) at the mRNA and enzyme protein levels in the intestine in Crohn's disease.

METHODS

Tissue samples were obtained from the intestine of 20 patients with Crohn's disease (seven operated and 13 colonoscopied) and from eight control patients without inflammatory diseases. The samples were studied by immunohistochemistry for PLA2-II enzyme protein and in situ hybridization for PLA2-II mRNA.

RESULTS

PLA2-II protein and mRNA were detected in the Paneth cells of the small intestinal mucosa in all patients and controls. PLA2-II protein and mRNA were found in the columnar epithelial cells of the small intestinal mucosa in six of eight and eight of eight patients with Crohn's ileitis, respectively. In the eight control patients PLA2-II protein and mRNA were not found in these cells (p = 0.007 and p < 0.001, respectively). Metaplastic Paneth cells, which consistently contained PLA2-II mRNA, were found in the colonic mucosa in five of six patients with Crohn's colitis and of one of eight control patients (p = 0.026). The columnar epithelial cells of the colonic mucosa contained PLA2-II protein in three of six and PLA2-II mRNA in six of six patients with Crohn's colitis, whereas the protein was found in these cells in none of eight of the controls (p = 0.055) and the mRNA in only one of eight (p = 0.005) controls.

CONCLUSIONS

In Crohn's disease, Paneth cells and columnar epithelial cells of the small and large intestinal mucosa synthesize PLA2-II at the site of active inflammation.

Regulation of the cellular expression of secretory and cytosolic phospholipases A2, and cyclooxygenase-2 by peptide growth factors

Secretory group II (sPLA2) and cytosolic (cPLA2) phospholipases A2 and cyclooxygenase-2 (Cox-2) play a pivotal role in release of proinflammatory eicosanoids. Excessive activity of sPLA2 per se can also propagate inflammation. Endogenous control of the above enzymes has not been completely elucidated. We investigated the combined impact of promoting cytokines and inhibitory peptide growth factors on the expression of mRNA of the above enzymes, on protein content and extracellular release of sPLA2 and on PGE2 production in osteoblasts (FRCO). The synthesis and release of sPLA2 were enhanced by about 20-fold by 0.5 ng/ml IL-1beta or by 50 ng/ml of TNFalpha. Coaddition of both cytokines resulted in synergistic 150-fold increase in the release of sPLA2 implying the existence of two paths of induction. IL-1beta and TNFalpha markedly enhanced the transcription of sPLA2 mRNA. Kinetic study showed that IL-1/TNF initiated sPLA2 release after 12 h, reaching maximum at 48 h. IL-1alpha was a weak stimulator of sPLA2 release, whereas IL-6, IL-8, IGF, IFN-gamma, growth hormone, insulin and GM-CSF were not stimulatory. Peptide growth hormones TGFbeta, PDGF-BB, EGF and bFGF markedly inhibited the extracellular release of sPLA2. TGFbeta and PDGF-BB significantly reduced the level of sPLA2 mRNA, thus acting upon transcription whereas EGF and bFGF were not inhibitory, acting rather upon the translational or posttranslational steps. IL-1/TNF and growth factors had no significant effect on cPLA2 mRNA expression. Cox-2 mRNA expression was markedly enhanced by IL-1/TNF and suppressed by all growth factors tested. Cytokines enhanced the extracellular release of PGE2 and further enhancement was induced by growth factors with the exception of TGFbeta. Cycloheximide abolished completely the release of sPLA2 and markedly reduced the release of PGE2 from cytokine-stimulated FRCO, regardless of whether growth factors were present or not. NS-398, a specific inhibitor of Cox-2 abolished almost completely the release of PGE2 from cytokine-stimulated cells, regardless of the presence of growth factors. Thus, different signalling mechanisms are involved in the impact of growth factors on mRNA expression of sPLA2, cPLA2 and Cox-2. The differences between the impact on FRCO sPLA2 and that reported in other cells, imply that endogenous control of arachidonic acid cascade is cell-specific.

Inhibition of serum phospholipase-A2 in acute pancreatitis by pharmacological agents in vitro

Phospholipase-A2 has been suggested as having a role in the pathophysiology of acute pancreatitis. The inhibition of phospholipase-A2 was studied in vitro using 17 pharmacological agents in the search for a specific therapy for acute pancreatitis. The inhibitory effect was tested using an isotopic assay system with 2-palmitoyl-(1-14C)-labelled dipalmitoyl phosphatidylcholine as a substrate and 10 microliters of serum from patients with acute necrotizing pancreatitis as an enzyme source. Among all agents tested, anti-inflammatory drugs inhibited enzyme activity most significantly: indomethacin (9.0 x 10(-3) mol l-1) decreased the phospholipase-A2 activity to one- tenth. The weak inhibitory effect could also be demonstrated using a lower concentration of 2 x 10(-5) mol l-1, which can be achieved after intravenous administration of 50 mg of this drug. The other drugs inhibited the enzyme activity at concentrations higher than those achieved after intravenous injections in clinical use. Diclofenac (3.1 x 10(-2) mol l-1) reduced the phospholipase-A2 activity by 93%, ketoprofen (2.0 x 10(-2) mol l-1) or chlorpromazine (1.4 x 10(-2) mol l-1) by 90%, tobramycin (1.7 x 10(-2) mol l-1) by 84%, doxycycline (9.0 x 10(-3) mol l-1) by 61%, dexamethasone (1.7 x 10(-3) mol l-1) by 62%, methylprednisolone (3.8 x 10(-2) mol l-1) by 50%, and pindolol (1.0 x 10(-4) mol l-1) by 59%. A weak inhibition of phospholipase-A2 activity was demonstrated by betamethasone, bupivacaine, digoxin, hydrocortisone, lidocaine, metoprolol, propranolol, and vancomycin. Indomethacin proved the most potent of the tested agents in inhibiting phospholipase-A2 activity in serum from patients with acute pancreatitis and should be further studied in vivo.

Molecular mechanisms involved in the regulation of prostaglandin biosynthesis by glucocorticoids

The anti-inflammatory properties of glucocorticoids are attributed in part, to their interference with prostaglandin synthesis. Phospholipases A2 and cyclooxygenases, the key enzymes of prostaglandin biosynthesis, are targets of glucocorticoid action; the molecular mechanisms, however, are not yet understood in detail. Obviously, glucocorticoids can act at different levels of gene regulation depending on cell type and inducing stimulus. The current knowledge of glucocorticoid interference with phospholipase A2 and cyclooxygenase expression is summarized. In comparison with other nonsteroidal anti-inflammatory drugs, glucocorticoids are unique inasmuch as they also inhibit cytokine synthesis and expression of other inflammation-related enzymes. Based on a more detailed understanding of glucocorticoid action, it may be possible to therapeutically exploit the anti-inflammatory effects and at the same time avoid the unwanted metabolic actions of these steroids.

Half-life of interleukin-1 beta-induced group II phospholipase A2 in rat mesangial cells

Group II phospholipase A2 (sPLA2) has been implicated as an important agent involved in a number of inflammatory processes. Potent pro-inflammatory cytokines, such as interleukin-1 beta (IL-1 beta) and tumor necrosis factor (TNF) have been found to induce sPLA2 synthesis and release from many cell types among which mesangial cells. Although considerable research has been devoted to unravelling the mechanisms underlying the induction of sPLA2 not much is known about the time scale at which the cytokine elicited signals for sPLA2 induction persist in target cells. In this study we addressed that question by using rat renal mesangial cells as a model target cell. We found that after removal of IL-1 beta from the culture medium, the induced-sPLA2 synthesis continues at gradually decreasing rates for approximately 8 h. This is accompanied by a decrease in sPLA2 mRNA levels. Furthermore, with pulse-chase experiments we investigated the half-life of sPLA2 disappearance from the cells. This disappearance was found to be biphasic. A rapidly disappearing pool, constituting approx. 74% of the total, exhibited a half-life of 1.6 +/- 0.2 h. The remaining pool of the induced enzyme was much more stable and its level remained constant for at least 24 h. Analysis of the appearance of newly synthesized enzyme in the culture medium indicated this process to be completed in an hour.

Membrane modifications in human erythroleukemia K562 cells during induction of programmed cell death by transforming growth factor beta 1 or cisplatin

Transforming growth factor beta 1 (TGF beta 1) and cisplatin induce apoptosis (programmed cell death, PCD) in human erythroleukemia K562 cells in an additive manner. After PCD was induced in K562 cells, analysis of phospholipid composition, fatty acids and cholesterol content in their membranes showed a decrease in phosphatidylethanolamine and an increase in phosphatidylserine, cardiolipin and phosphatidic acid. Moreover, cisplatin but not TGF beta 1 enhanced sphingomyeline levels in apoptotic cells, whereas TGF beta 1 increased the amount of linoleic acid and, more remarkably, of cholesterol. The combination TGF beta 1 + cisplatin produced membrane changes similar to those provoked by each inducer individually. Furthermore, the specific activities of 5-lipoxygenase and cytosolic phospholipase A2, both modulating the physical properties of membranes and membrane-lipid-mediated intracellular signalling, were enhanced by treatment with TGF beta 1 or TGF beta 1 + cisplatin. These findings highlight the profound changes in cell membranes during the biochemical events of the apoptotic pathway.

Purification and characterization of nuclear alkaline phospholipase A2 in rat ascites hepatoma cells

The alkaline phospholipase A2 (PLA2) was purified from nuclei of rat ascites hepatoma cells (AH7974) by column chromatography with a Sephacryl S-300 column and an immunoadsorbent using anti-group II PLA2 monoclonal antibody. From these two columns, the alkaline PLA2 was eluted in parallel with a 17-kDa protein which is reactive to another anti-group II PLA2 polyclonal antibody. Approximately 80% of nuclear PLA2 was inhibited by this antibody. The alkaline PLA2 was found in association with the chromatin fraction among subnuclear fractions. By an immunocytochemical staining, the nuclei of AH7974 were stained more strongly than other parts of cells with anti-group II PLA2 antiserum.

Effects of dexamethasone and transforming growth factor-beta 2 on group II phospholipase A2 mRNA and activity levels in interleukin 1 beta- and forskolin-stimulated mesangial cells

The expression of 14 kDa group II phospholipase A2 [also referred to as secretory PLA2 (sPLA2)] is induced in rat glomerular mesangial cells by exposure to inflammatory cytokines and forskolin, a cAMP elevating agent. Previously we have shown that dexamethasone and transforming growth factor-beta 2 (TGF-beta 2) suppress sPLA2 protein synthesis and enzyme activity induced by cytokines and forskolin. The regulation of sPLA2 by pro-inflammatory cytokines suggests that the enzyme may play a role in glomerular inflammatory reactions. In order to understand the regulation of sPLA, in more detail, we investigated whether dexamethasone and TGF-beta 2 also suppress sPLA, mRNA after its induction by either interleukin-1 beta (IL-1 beta) or forskolin. We found that IL-1 beta-induced sPLA2 mRNA in rat mesangial cells is not down-regulated by pretreatment of the cells with dexamethasone, even at a concentration of 10 microM, which dramatically decreases sPLA2 protein levels and activity. Metabolic labelling experiments indicated that the decreased sPLA2 levels under these conditions can be explained by inhibition of the rate of sPLA2 synthesis from the elevated mRNA levels. In contrast, the forskolin-induced elevation of sPLA, mRNA is inhibited by dexamethasone in a concentration-dependent manner. Likewise, TGF-beta 2 inhibits the elevation of sPLA, mRNAs induced by either IL-1 beta or forskolin. The decrease in sPLA2 mRNA caused by TGF-beta 2 corresponds with the decrease in sPLA2 enzyme levels and activity. These data suggest that cytokine- and forskolin-induced sPLA2, expression is tightly controlled via both transcriptional and post-transcriptional mechanisms. Furthermore, we show that pretreatment of mesangial cells with epidermal growth factor prior to stimulation with IL-1 beta or forskolin had no suppressing effect on sPLA2 levels or enzyme activity, as has been reported previously for osteoblasts.