title: Expression pattern and role of a 60-kilodalton progesterone binding protein in regulating granulosa cell apoptosis: involvement of the mitogen-activated protein kinase cascade.
abstract: Progesterone (P4) inhibits both granulosa cells and spontaneously immortalized granulosa cells (SIGCs) from undergoing apoptosis. P4 does so through a plasma membrane-initiated event. It appears that P4's membrane-initiated actions are mediated by a 60-kDa P4 binding protein (P4BP), which is detected by an antibody directed against the ligand binding domain of the nuclear P4 receptor (i.e., C-262). Immunohistochemical analysis revealed that a C-262-detectable protein was first observed in the periphery of a few granulosa cells within early antral-stage follicles. In nonatretic antral follicles, this protein was detected at the periphery of virtually all granulosa cells. In contrast, granulosa cells of atretic follicles lost the distinct peripheral localization of this C-262-detectable protein. This reduction in the membrane localization was also observed by Western blot analysis. To assess the temporal changes in this 60-kDa P4BP during apoptosis, studies were conducted using SIGCs. That this 60-kDa protein is important in mediating P4's action was confirmed by the observation that C-262 but not IgG attenuated P4's antiapoptotic action. Interestingly, the membrane localization of this 60-kDa P4BP was maintained but the ability of P4 to prevent apoptosis was lost within 20 min of initiating the apoptotic cascade. In addition, Erk-1 and -2 phosphorylation (i.e., activity) increased within 20 min of P4 withdrawal. Further, P4 suppressed the increase in the Erk-1 phosphorylation if administered within 5 but not 20 min of initiating the apoptotic cascade. Moreover, the mitogen-activated protein kinase kinase (MEK) inhibitor, PD98059, reduced the percentage of SIGCs undergoing apoptosis in the absence of P4. Because MEK phosphorylates Erk, these observations suggests that 1) the increase in Erk-1 activity is an important part of the apoptotic cascade, 2) P4 promotes granulosa cell viability by modulating the activity of Erk-1, and 3) P4 becomes "uncoupled" from its antiapoptotic signal transduction mechanism within 20 min of initiating apoptosis, even though the membrane localization of the 60-kDa P4BP is maintained.
authors.affiliation: Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA. peluso@nso2.uchc.edu
authors.forename: J J
authors.initials: JJ
authors.lastname: Peluso
authors.forename: T
authors.initials: T
authors.lastname: Bremner
authors.forename: G
authors.initials: G
authors.lastname: Fernandez
authors.forename: A
authors.initials: A
authors.lastname: Pappalardo
authors.forename: B A
authors.initials: BA
authors.lastname: White
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D006107:Granulosa Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008970:Molecular Weight; D011374:Progesterone / Q000378:metabolism / Q000494:pharmacology; D011376:Progesterone-Binding Globulin / Q000737:chemistry / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D011376:Progesterone-Binding Globulin; D011374:Progesterone; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020929:Mitogen-Activated Protein Kinase Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one