In vitro modulation of the expression of 15-hydroxy-prostaglandin dehydrogenase by trophoblast differentiation

Prostaglandin catabolic enzymes as tumor suppressors

15-Hydroxyprostaglandin dehydrogenase (15-PGDH) is a key prostaglandin catabolic enzyme catalyzing the oxidation and inactivation of prostaglandin E(2) (PGE(2)) synthesized from the cyclooxygenase (COX) pathway. Accumulating evidence indicates that 15-PGDH may function as a tumor suppressor antagonizing the action of COX-2 oncogene. 15-PGDH has been found to be down-regulated contributing to elevated levels of PGE(2) in most tumors. The expression of 15-PGDH and COX-2 appears to be regulated reciprocally in cancer cells. Down-regulation of 15-PGDH in tumors is due, in part, to transcriptional repression and epigenetic silencing. Numerous agents have been found to up-regulate 15-PGDH by down-regulation of transcriptional repressors and by attenuation of the turnover of the enzyme. Up-regulation of 15-PGDH may provide a viable approach to cancer chemoprevention. Further catabolism of 15-keto-prostaglandin E(2) is catalyzed by 15-keto-prostaglandin-∆(13)-reductase (13-PGR), which also exhibits LTB(4)-12-hydroxydehydrogenase (LTB(4)-12-DH) activity. 13-PGR/LTB(4)-12-DH behaves as a tumor suppressor as well. This review summarizes current knowledge of the expression and function of 15-PGDH and 13-PGR/LTB(4)-12-DH in lung and other tissues during tumor progression. Future directions of research on these prostaglandin catabolic enzymes as tumor suppressors are also discussed.

Prostaglandin dehydrogenase (PGDH) in granulosa cells of primate periovulatory follicles is regulated by the ovulatory gonadotropin surge via multiple G proteins

The ovulatory gonadotropin surge increases granulosa cell prostaglandin synthesis as well as prostaglandin dehydrogenase (PGDH), the key enzyme responsible for prostaglandin metabolism. To investigate gonadotropin regulation of PGDH in the primate follicle, monkey granulosa cells were obtained across the 40-h periovulatory interval. PGDH activity was low before the ovulatory hCG stimulus, peaked 12-24 h after hCG, and was low again 36 h after hCG administration. Granulosa cells maintained in vitro with hCG showed a similar temporal pattern of PGDH. The LH/CG receptor can utilize multiple signaling pathways to regulate intracellular events. Gonadotropin-stimulated cAMP appears to act primarily via the Epacs to increase PGDH mRNA, protein, and activity. In contrast, PLC activation of PKC likely decreases PGDH mRNA, protein, and activity late in the periovulatory interval. Increased, then decreased PGDH activity may delay accumulation of prostaglandins in the follicle until late in the periovulatory interval, contributing to timely ovulation in primates.

Effect of calcium ionophore A23187 on prostaglandin synthase type 2 and 15-hydroxy-prostaglandin dehydrogenase expression in human chorion trophoblast cells

OBJECTIVE

Prostaglandins induce parturition in humans. Prostaglandin output is regulated by the synthetic and metabolic enzymes, prostaglandin synthase type 2 (PTGS2) and 15-hydroxyprostaglandin dehydrogenase (PGDH). The role of calcium in regulating PTGS2 and PGDH expression was investigated in chorion trophoblasts.

STUDY DESIGN

Cells were treated with calcium ionophore A23187 in the presence or absence of calcium chelators; changes in messenger ribonucleic acid expression were measured with real-time polymerase chain reaction and analyzed with analysis of variance. Protein expression was evaluated with Western blot and dual immunofluorescence.

RESULTS

A23187 stimulated PTGS2 and suppressed PGDH expression. Effects of A23187 were reversed by calcium chelators. PTGS2 had perinuclear and cytosolic distribution, whereas PGDH was cytosolic. Some cells expressed both enzymes, some neither enzyme, and some either PTGS2 or PGDH.

CONCLUSION

Chorion cells showed heterogeneity in the expression of PTGS2 and PGDH. Calcium influx regulates PTGS2 and PGDH expression, thereby promoting coordinated increased prostaglandin output in circumstances such as term and preterm labor.

Loss of 15-hydroxyprostaglandin dehydrogenase expression disrupts urothelial differentiation

OBJECTIVES

Urothelial differentiation is essential for the maintenance of urinary bladder function. We explored the expression and function of 15-hydroxyprostaglandin dehydrogenase (PGDH) during urothelial differentiation.

METHODS

We evaluated expression of PGDH by Northern and Western blotting and immunostaining in human urothelial cultures, cell lines, and tissues. We determined enzymatic function using enzyme-linked immunosorbent assay. Small inhibitory ribonucleic acids were used to inhibit PGDH expression in human bladder cancer cells.

RESULTS

We found PGDH messenger ribonucleic acid was increased in an in vitro model of human urothelial differentiation by Northern blotting. Western blotting of human bladder cancer cell lines showed expression in the well-differentiated RT4 cells and no expression in poorly differentiated UC3 cells. Immunostaining showed that PGDH expression increased with differentiation in normal bladder urothelium. The enzyme was functional in the well-differentiated RT4 human bladder cancer cell line. Inhibition of PGDH expression resulted in disruption of E-cadherin expression at cell-cell contacts in well-differentiated RT4 bladder cancer cells.

CONCLUSIONS

These studies indicate that PGDH expression is associated with urothelial differentiation, and loss of PGDH expression results in disruption of urothelial differentiation.

Suppression of 15-Hydroxyprostaglandin Dehydrogenase Messenger RNA Concentration, Protein Expression, and Enzymatic Activity during Human Ureteral Obstruction

Prostanoids produce significant effects in the ureter, particularly in response to obstruction. Ureteral obstruction is associated with increased prostanoid synthesis via cyclooxygenase induction; however, prostaglandin degradation mediated by 15-hydroxyprostaglandin dehydrogenase (PGDH) has not been evaluated in the ureter. The purpose of this study was to determine whether PGDH steady-state mRNA, protein, and enzyme activity are altered in the human ureter during obstruction. Human ureteral segments from patients undergoing donor nephrectomy (normal segments) or ureteral stricture repair (obstructed segments) were obtained with proper informed consent. We evaluated PGDH steady-state mRNA relative to ribosomal protein S26 reference gene by reverse transcription-polymerase chain reaction and Vistra Green fluoroimaging. We determined PGDH protein content relative to glyceraldehyde-3-phosphate dehydrogenase by immunoblotting and PGDH localization by immunohistochemistry. PGDH enzymatic activity was determined by measurement of conversion of 15-hydroxy- to 15-keto-prostaglandin using thin layer chromatography separation. We found that PGDH mRNA and protein were decreased 4- to 6-fold, and enzyme activity was decreased >3-fold in obstructed human ureter relative to normal controls. PGDH was localized to the urothelial cells, with little or no expression in smooth muscle. Our results indicate that PGDH mRNA, protein, and enzyme activity are suppressed in the human ureter during obstruction. Increased concentrations of prostanoids subsequent to ureteral obstruction seem to be due to decreased degradation as well as increased synthesis. Modulation of prostanoid degradation may have therapeutic relevance in obstructive disorders of the ureter.

Hypoxia attenuates PGE(2)but increases prostacyclin and thromboxane production in human term villous trophoblast

Prostanoids have been proposed to play a major role in the regulation of uteroplacental blood flow. We examined the effect of hypoxia on the production of prostaglandin E(2)(PGE(2)) thromboxane B(2)(TXB(2)), and prostacyclin (measured as 6-keto-PGF(1alpha)) by human term trophoblast cells and villous placental explants. Explants (n=8) and purified trophoblast cells (n=5) were incubated for 24-72 h under either normoxic (21 per cent O(2)) or hypoxic (2 per cent O(2)) conditions. In trophoblast monolayer cultures, hypoxia attentuated PGE(2)production rates to 52+/-9.4 per cent (mean+/-sem, P< 0.05) but recovered to control rates within 48 h. In villous explants, PGE(2)production was significantly decreased after 48 and 72 h of hypoxia versus the normoxic control, accompanied by increased production of 6-keto-PGF(1alpha)to 173.9+/-26.7 per cent after 48 h. TXB(2)production was increased to 172.3+/-25.9 per cent and 653.2+/-135.7 per cent (P< 0.05) control after 48 and 72 h of hypoxia, respectively. These results were confirmed in villous explants (n=3) cultured in the presence of exogenous 10 microm arachidonic acid. Hypoxia had no significant effect on TXB(2)and 6-keto-PGF(1alpha)in trophoblast cells. In summary, our findings suggest that hypoxia could be responsible for abnormal profiles of prostanoid production commonly observed in women with pre-eclampsia. These results indicate a putative link between hypoxia and compromised placental perfusion.

Endocrine and paracrine regulation of birth at term and preterm

We have examined factors concerned with the maintenance of uterine quiescence during pregnancy and the onset of uterine activity at term in an animal model, the sheep, and in primate species. We suggest that in both species the fetus exerts a critical role in the processes leading to birth, and that activation of the fetal hypothalamic-pituitary-adrenal axis is a central mechanism by which the fetal influence on gestation length is exerted. Increased cortisol output from the fetal adrenal gland is a common characteristic across animal species. In primates, there is, in addition, increased output of estrogen precursor from the adrenal in late gestation. The end result, however, in primates and in sheep is similar: an increase in estrogen production from the placenta and intrauterine tissues. We have revised the pathway by which endocrine events associated with parturition in the sheep come about and suggest that fetal cortisol directly affects placental PGHS expression. In human pregnancy we suggest that cortisol increases PGHS expression, activity, and PG output in human fetal membranes in a similar manner. Simultaneously, cortisol contributes to decreases in PG metabolism and to a feed-forward loop involving elevation of CRH production from intrauterine tissues. In human pregnancy, there is no systemic withdrawal of progesterone in late gestation. We have argued that high circulating progesterone concentrations are required to effect regionalization of uterine activity, with predominantly relaxation in the lower uterine segment, allowing contractions in the fundal region to precipitate delivery. This new information, arising from basic and clinical studies, should further the development of new methods of diagnosing the patient at risk of preterm labor, and the use of scientifically based strategies specifically for the management of this condition, which will improve the health of the newborn.

The human NAD+-dependent 15-hydroxyprostaglandin dehydrogenase gene promoter is controlled by Ets and activating protein-1 transcription factors and progesterone

NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) is a key catabolic enzyme in the inactivation of PGF2alpha and PGE2 and therefore serves as an important determinant in regulating their local concentrations. To gain insights into the transcriptional regulation of this enzyme, we have isolated 3.5 kb of the 5'-flanking sequence of the human PGDH promoter and characterized its control in hemopoietic cells and cells of myometrial and placental origin. Several potential binding sites for cAMP-responsive element-binding protein (CREB), Ets, and activating protein-1 (AP-1) transcription factors are present within 2368 bp of the 5'-flanking region. This region and deletions thereof were fused to the luciferase reporter gene and used for transient transfection experiments. In Jurkat leukemic T cells, which express PGDH endogenously, the transfected PGDH promoter was strongly induced by phorbol ester. Induction was reversed by coexpression of A-Fos, a dominant negative to AP-1. In primary cultures of myometrial smooth muscle cells (SMC), the Ets family members Ets-1, Ets-2, and PEA3 potently stimulated transcriptional activity of the PGDH promoter. PEA3-mediated activation was partially repressed by A-Fos, suggesting an involvement of AP-1 proteins, which might be conferred by a distal and a proximal Ets/ AP-1 composite element. The distal Ets/AP-1 element is flanked by two CRE-like sequences. Cotransfection of A-CREB, a dominant negative to CREB, inhibited stimulation of PGDH-2368/luc3 by PEA3 in myometrial SMC, whereas treatment with 8-bromo-cAMP moderately enhanced promoter activity. Progesterone is believed to be an important stimulus for PGDH expression in the utero-placental unit, thus contributing to the maintenance of a quiescent uterus during pregnancy. In myometrial SMC, both isoforms of the progesterone receptor, PR-B and PR-A, caused a ligand-dependent activation of PGDH-2368/luc3. Transcriptional activity of PR-B, but not PR-A, was further enhanced by the addition of 8-bromo-cAMP. We could not confirm a recently proposed transcriptional control of PGDH by mineralocorticoid receptor. No effect of mineralocorticoid receptor, in the absence or presence of aldosterone, with or without 8-bromo-cAMP, was observed on PGDH-2368/luc3. Taken together, these findings demonstrate control of the PGDH promoter by multiple pathways and provide evidence for cross-talk among Ets, AP-1, cAMP, and PR-mediated signaling, suggesting complex regulatory mechanisms for the expression of PGDH.