Recovery of prostaglandin synthesis in rat glomerular mesangial cells after aspirin inhibition: induction of cyclooxygenase activity by serum and epidermal growth factor

Effect of EGF on H2O2-induced inhibition of ?-MG uptake in renal proximal tubule cells: Involvement of MAPK and AA release

Both oxidative stress and epidermal growth factor (EGF) contribute to the initiation and progression of renal proximal tubular dysfunction under pathophysiologic conditions. Thus, this study was performed (1) to examine both the individual, and the combined effects of H2O2 and EGF on alpha-methyl-D-glucopyranoside uptake (alpha-MG uptake) in the primary cultured renal proximal tubule cells (PTCs), and (2) to elucidate the involvement of p44/42 mitogen activated protein kinase (MAPK) and phospholipase A2 in mediating these actions. Both H2O2 and EGF inhibited alpha-MG uptake individually, while the combination of H2O2 and EGF further potentiated the inhibitory effect on alpha-MG uptake, which was elicited by each agent. H2O2 not only caused a rapid increase in the phosphorylation of p44/42 MAPK, but also promoted the translocation of cytosolic phospholipase A2 (cPLA2) from the cytosolic to particulate fraction, and stimulated cellular [3H]-arachidonic acid (AA) release. EGF similarly activates phosphorylation of p44/42 MAPK and stimulates [3H]-AA release. When PTCs were exposed to 100 microM H2O2 and 50 ng/ml EGF simultaneously, a further increase in the phosphorylation of p44/42 MAPK, of [3H]-AA release, and of prostaglandin E2 (PGE2) production was elicited as compared with the effects of each individual agonist alone. Moreover, the additive phosphorylation of p44/42 MAPK, [3H]-AA release, and PGE2 production by H2O2 and EGF was almost completely inhibited by the p44/42 MAPK inhibitor, PD 98059. In conclusion, these results are consistent with the hypothesis that under conditions of oxidative stress, the H2O2-induced inhibition of alpha-MG uptake in the renal proximal tubule is mediated through a modulation of the EGF signaling pathway, promoting further phosphorylation of p44/42 MAPK, activation of PLA2.

Epidermal growth factor inhibits14C-?-methyl-d-glucopyranoside uptake in renal proximal tubule cells: Involvement of PLC/PKC, p44/42 MAPK, and cPLA2

The effect of EGF on (14)C-alpha-methyl-D-glucopyranoside (alpha-MG) uptake and its related signaling pathways were examined in primary cultured rabbit renal proximal tubule cells (PTCs). Epidermal growth factor (EGF) (50 ng/ml) was found to inhibit alpha-MG uptake, a distinctive proximal tubule marker. The EGF effect was blocked by AG1478 (an EGF receptor antagonist) or genistein and herbimycin (tyrosine kinase inhibitors), respectively. In addition, the EGF-induced inhibition of alpha-MG uptake was blocked by neomycin and U73122 (phospholipase C inhibitors) as well as staurosporine, H-7, and bisindolylmaleimide I (protein kinase C inhibitors). EGF was also observed to increase inositol phosphate formation. Furthermore, both the EGF-induced inhibition of alpha-MG uptake and increase of arachidonic acid (AA) release were blocked by AACOCF(3) (a cytosolic phospholipase A(2) inhibitor), indomethacin (a cyclooxygenase inhibitor), and econazole (a cytochrome P-450 epoxygenase inhibitor). We examined the involvement of mitogen-activated protein kinases (MAPKs) in mediating the effect of EGF on alpha-MG uptake. Indeed, EGF increased phosphorylation of p44/p42 MAPK and the EGF-induced inhibition of alpha-MG uptake as well as the stimulatory effect of EGF on AA release was blocked by PD 98059 (a p44/42 MAPK inhibitor), suggesting a causal relationship. However, inhibitors of PKC also prevented the EGF-induced increase of AA release. In conclusion, EGF partially inhibited alpha-MG uptake via PLC/PKC, p44/42 MAPK, and PLA(2) signaling pathways.

Regulation of prostaglandin H synthase-2 expression in cerebromicrovascular smooth muscle by serum and epidermal growth factor

Growth factors may play a role in the formation of prostaglandins (PG) by cerebral blood vessels during development or reaction to injury. In smooth muscle cultures isolated from murine cerebral microvessels PG production was induced with either serum or epidermal growth factor (EGF). Prostaglandin H synthase (PGHS) activity peaked at 6 h after the addition of 10% serum or 50 ng/ml EGF. Increases in expression of PGHS-1 mRNA were small (7- to 10-fold) compared with PGHS-2 (30- to 120-fold), and the induction patterns were different for serum and EGF. An increase in PGHS-2 message was detected by 0.5 h of adding either agent, but peak induction occurred earlier for EGF than for serum, 1 h vs. 3 h, respectively. The response to either stimulus had returned to prestimulation levels by 12 h. The induction of PGHS-2 protein was also transient, but followed a more delayed time course (peak levels at 6 h). Induction of activity, message, and protein by either agent was blocked by 1 microM dexamethasone and attenuated by genistein (100 microM), a nonspecific tyrosine kinase inhibitor. Tyrphostin 47, a more selective EGF receptor tyrosine kinase inhibitor, dose-dependently inhibited EGF-stimulated PGHS activity, completely abolishing PG production at 100 microM. However, this inhibitor had no effect on serum-stimulated PG production. Curiously, 100 microM tyrphostin 47 enhanced EGF-induced PGHS-2 mRNA and protein expression. These data suggest that EGF induces the expression of PGHS-2 in cerebromicrovascular smooth muscle by a mechanism that requires tyrosine kinase activity and that is distinct from serum.

Staphylococcal exoproducts down-regulate cyclooxygenase 1 and 2 in peritoneal macrophages

Peritoneal macrophages (PMOs) are important components of the host defense against microbial infection in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Incubation of human PMOs with cell-free supernatant (BFS), prepared from Staphylococcus aureus, inhibited prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) production. Slot-blot analysis of cyclooxygenase-1 (Cox-1) and Cox-2 demonstrated a decrease in both Cox-1 (29%) and, to a greater extent, Cox-2 (65%) protein expression after BFS stimulation. When competitive polymerase chain reaction (PCR) was used, the peak levels of Cox-1 and Cox-2 messenger ribonucleic acid (mRNA) in unstimulated PMOs were 0.304+/-0.13 pmol/L and 9.61+/-2.84 pmol/L (mean+/-SEM, n = 3), respectively. After exposure of samples to BFS for 30 minutes, the level of Cox-2 mRNA was reduced to 0.59+/-0.449 pmol/L (16-fold reduction, p < 0.05), and the level of Cox-1 mRNA was reduced to 0.02+/-0.002 pmol/L (15-fold reduction, p < 0.05). In contrast, these same PMOs showed an increased expression of IL-6 mRNA and increased secretion of IL-6 protein. These results indicate that prostaglandin production in PMOs is regulated by alterations in both immunoreactive Cox-1 and Cox-2. The down-regulation of Cox metabolism in these cells is primarily related to the delayed and depressed increase in the Cox-2 gene product.

Prostaglandin production in cultured cerebral microvascular smooth muscle is serum dependent

To expand the understanding of cerebrovascular eicosanoid metabolism, the ability of smooth muscle isolated from murine cerebral microvessels to produce prostaglandins (PGs) was studied in vitro. Cultures from SJL and BALB/c mice produced primarily prostaglandin E2 (PGE2) and I2 (PGI2) in response to exogenous arachidonate and calcium ionophore as well as the agonists acetylcholine and epinephrine. Subconfluent smooth muscle cultures demonstrated a two- to threefold increased capacity to produce PG compared with confluent cultures. In contrast, serum deprivation of smooth muscle caused an 80-90% diminution in both PGE2 and PGI2 production but had no effect on PG release in cerebromicrovascular endothelium. Reintroduction of serum to smooth muscle restored PG production within 6h, and the restoration was inhibited by 1 microM dexamethasone. Message for both prostaglandin H synthase (PGHS)-1 and -2 was detectable in smooth muscle grown in the presence of serum, but PGHS-2 message was not present in serum-deprived cultures. Furthermore, readdition of serum induced a massive increase in PGHS-2 mRNA with only a small increase in PGHS-1 message. The serum induction of PGHS-2 was corroborated by immunohistochemistry and Western blotting. Thus cerebromicrovascular smooth muscle may contribute significantly to the formation of PG under circumstances likely to be present during central nervous system pathologies. The induction of PGHS, particularly PGHS-2, may play a key role in this process.

Mechanical stretch/relaxation of cultured rat mesangial cells induces protooncogenes and cyclooxygenase

In cultured rat glomerular mesangial cells, continuous cycles of stretching and relaxation (stretch/relaxation) stimulate cell proliferation, protein synthesis, and prostaglandin production. We examined regulation of gene expression that may underlie these alterations in cell functions. Stretch/relaxation caused time-dependent induction of the immediate early genes, c-fos and zif 268/egr-1, with maximal increases occurring between 15 and 30 min. The mitogen-inducible prostaglandin G2/H2 synthase (PGH2S-2) gene was also induced within 30 min of stretch/relaxation, with concomitant increases in the immunoreactive PGH2S-2 protein. These gene inductions were preceded by transient translocation of protein kinase C activity from cytosol to membrane as well as by increases in 45Ca2+ uptake and total cellular calcium content. The stretch/relaxation-induced expression was suppressed by protein kinase C inhibition, whereas less profound inhibition was observed with inhibition of calcium influx in low (100 nM) calcium buffer. These findings indicate that in mesangial cells mechanical stress induces expression of the protooncogenes and the mitogen-inducible cyclooxygenase primarily through protein kinase C-dependent mechanisms.

Fibroblast growth factor upregulates PGG/H synthase in rabbit microvascular endothelial cells by a glucocorticoid independent mechanism

The present study was undertaken to determine the effects of acidic fibroblast growth factor (aFGF) on eicosanoid synthesis in microvessel endothelial cells derived from rabbit left ventricular muscle (RCME cells). We observed that aFGF increased AA conversion to PGE2 in a time- and dose-dependent manner, and the stimulatory effect was abolished by actinomycin D and cycloheximide. Acidic FGF increased the recovery of PGG/H synthase activity following aspirin treatment, suggesting an action on de novo PGG/H synthase synthesis. Acidic FGF increased the incorporation of [35S] methionine into a 70 kD immunoreactive PGG/H synthase band. PGG/H synthase synthesis following aspirin treatment was also increased by transforming growth factor beta, while epidermal growth factor basic FGF and platelet derived growth factor were without effect. In addition, the actions of aFGF on de novo PGG/H synthase were compared in several endothelial preparations. Acidic FGF treatment of aspirin treated endothelial cells from rabbit lung microvessels and small pulmonary artery and from human lung microvessels all showed an increase in PGG/H synthase recovery. In contrast, similar treatment of human umbilical vein endothelial cells was without effect. Pretreatment of RCME cells with dexamethasone (1 microM) did not alter the aFGF induction of PGG/H synthase activity. We conclude that aFGF stimulates PGE2 production by a mechanism that includes the de novo synthesis of PGG/H synthase. This mechanism appears to be distinct from previously described glucocorticoid sensitive translational controls of PG synthase synthesis by epidermal growth factor in smooth muscle and mesangial cells.