title: Identification of a functional link for the p53 tumor suppressor protein in dexamethasone-induced growth suppression.
abstract: Serine/threonine phosphatase 5 (PP5) can act as a suppresser of p53-dependent growth suppression and has been reported to associate with several proteins, including the glucocorticoid receptor/heat-shock protein-90 complex. Still, the physiological/pathological roles of PP5 are unclear. To characterize the relationship of PP5, glucocorticoid receptor activation and p53, here we describe the development of chimeric antisense oligonucleotides that potently inhibit human p53 expression. This allowed us to regulate the expression of either p53 (e.g. with ISIS 110332) or PP5 (e.g. with ISIS 15534) in genetically identical cells. Studies with ISIS 110332 revealed that the suppression of p53 expression is associated with a decrease in the basal expression of the cyclin-dependent kinase inhibitor protein, p21(WAF1/Cip1), and a concomitant increase in the rate of cell proliferation. Suppression of p53 also blocks dexamethasone-induced p21(WAF1/Cip1) expression and G(1)-growth arrest. Furthermore, treatment with ISIS 110332, but not the mismatched controls, ablates the suppression of growth produced by prior treatment with dexamethasone. Additional studies revealed that dexamethasone-dependent p21(WAF1/Cip1) expression occurs without an apparent change in p53 protein levels or the phosphorylation status of p53 at Ser-6, -37, or -392. However, dexamethasone treatment is associated with an increase in p53 phosphorylation at Ser-15. Suppression of PP5 expression with ISIS 15534 also results in the hyperphosphorylation of p53 at Ser-15. Together, these findings indicate that the basal expression of p53 plays a functional role in a glucocorticoid receptor-mediated response regulating the expression of p21(Waf1/Cip1) via a mechanism that is suppressed by PP5 and associated with the phosphorylation of p53 at Ser-15.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, Alabama 36688, USA.
authors.forename: Gudrun
authors.initials: G
authors.lastname: Urban
authors.forename: Teresa
authors.initials: T
authors.lastname: Golden
authors.forename: Ileana V
authors.initials: IV
authors.lastname: Aragon
authors.forename: Lex
authors.initials: L
authors.lastname: Cowsert
authors.forename: Scott R
authors.initials: SR
authors.lastname: Cooper
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Dean
authors.forename: Richard E
authors.initials: RE
authors.lastname: Honkanen
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D015152:Blotting, Northern; D015153:Blotting, Western; D002455:Cell Division; D002469:Cell Separation; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D016193:G1 Phase; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D016192:Resting Phase, Cell Cycle; D012694:Serine / Q000737:chemistry; D013997:Time Factors; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism / Q000502:physiology*
chemical_list: D018931:Antineoplastic Agents, Hormonal; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009687:Nuclear Proteins; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D012694:Serine; D003907:Dexamethasone; D008156:Luciferases; D010749:Phosphoprotein Phosphatases; C089641:protein phosphatase 5