title: Tyrosine kinase inhibitors block the glucocorticoid stimulation of prostaglandin endoperoxide H synthase expression in amnion cells.
abstract: Human amnion cells in primary culture respond to glucocorticoids in a characteristic fashion by the increased expression of the inducible prostaglandin endoperoxide H synthase isoenzyme, PGHS-2. Since PGHS-2 induction by agonists generally involves tyrosine kinases, we examined the possibility that the glucocorticoid stimulation of PGHS-2 in the amnion cells is tyrosine kinase dependent. PGHS-2 expression was stimulated in confluent, serum-starved amnion cells with dexamethasone, and the effect of the tyrosine kinase inhibitors herbimycin A and tyrphostins AG126, AG1288, and A1 on enzyme activity induction was determined. All four inhibitors blocked the increase of PGHS activity in a concentration-dependent manner with IC50 values of 0.077 +/- 0.05, 15.38 +/- 5.14, 20.91 +/- 3.1, and 29.77 +/- 8.21 microM, respectively (mean +/- SE, n = 4). Dexamethasone increased (approximately twofold) the tyrosine phosphorylation of 120-, 110-, and 77-kDa proteins in cell extracts, and herbimycin A selectively blocked the phosphorylation of the 110-kDa phosphoprotein. The stimulation of the steady-state level of PGHS-2 mRNA by dexamethasone was also inhibited by herbimycin A. These results suggest that glucocorticoids induce PGHS-2 expression in amnion cells with the involvement of tyrosine kinase(s). The role of tyrosine kinase dependent mechanisms in the control of amnion cell responsiveness to corticosteroids remains to be established.
authors.affiliation: University of Alberta Perinatal Research Centre, Department of Obstetrics and Gynaecology, Edmonton, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Zakar
authors.forename: J E
authors.initials: JE
authors.lastname: Mijovic
authors.forename: D
authors.initials: D
authors.lastname: Bhardwaj
authors.forename: D M
authors.initials: DM
authors.lastname: Olson
mesh_terms: D000650:Amnion / Q000201:enzymology*; D016227:Benzoquinones; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D006801:Humans; D047029:Lactams, Macrocyclic; D011247:Pregnancy; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis* / Q000235:genetics; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology; D011809:Quinones / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D017828:Rifabutin / Q000031:analogs & derivatives
chemical_list: D016227:Benzoquinones; D004791:Enzyme Inhibitors; D047029:Lactams, Macrocyclic; D011809:Quinones; D012333:RNA, Messenger; D017828:Rifabutin; C020754:herbimycin; D003907:Dexamethasone; D011451:Prostaglandin-Endoperoxide Synthases; D011505:Protein-Tyrosine Kinases