title: Cross talk of signaling pathways in the regulation of the glucocorticoid receptor function.
abstract: Several posttranslational modifications including phosphorylation have been detected on the glucocorticoid receptor (GR). However, the interdependence and combinatorial regulation of these modifications and their role in GR functions are poorly understood. We studied the effects of c-Jun N-terminal kinase (JNK)-dependent phosphorylation of GR on its sumoylation status and the impact that these modifications have on GR transcriptional activity. GR is targeted for phosphorylation at serine 246 (S246) by the JNK protein family in a rapid and transient manner. The levels of S246 phosphorylation of endogenous GR increased significantly in cells treated with UV radiation that activates JNK. S246 GR phosphorylation by JNK facilitated subsequent GR sumoylation at lysines 297 and 313. GR sumoylation increased with JNK activation and was inhibited in cells treated with JNK inhibitor. GR sumoylation in cells with activated JNK was mediated preferentially by small ubiquitin-like modifier (SUMO)2 rather than SUMO1. An increase in GR transcriptional activity was observed after inhibition of JNK or SUMO pathways and suppression of GR transcriptional activity after activation of both pathways in cells transfected with GR-responsive reporter genes. Endogenous GR transcriptional activity was inhibited on endogenous target genes IGF binding protein (IGFBP) and glucocorticoid-induced leucine zipper (GILZ) when JNK and SUMO pathways were induced individually or simultaneously. Activation of both of these signals inhibited GR-mediated regulation of human inhibitor of apoptosis gene (hIAP), whereas simultaneous activation had no effect. We conclude that phosphorylation aids GR sumoylation and that cross talk of JNK and SUMO pathways fine tune GR transcriptional activity in a target gene-specific manner, thereby modulating the hormonal response of cells exposed to stress.
authors.affiliation: The University of Manchester, Oxford Road, Manchester M13 9PT, UK.
authors.forename: Laura
authors.initials: L
authors.lastname: Davies
authors.forename: Nirupama
authors.initials: N
authors.lastname: Karthikeyan
authors.forename: James T
authors.initials: JT
authors.lastname: Lynch
authors.forename: Elin-Alia
authors.initials: EA
authors.lastname: Sial
authors.forename: Areti
authors.initials: A
authors.lastname: Gkourtsa
authors.forename: Constantinos
authors.initials: C
authors.lastname: Demonacos
authors.forename: Marija
authors.initials: M
authors.lastname: Krstic-Demonacos
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003907:Dexamethasone / Q000494:pharmacology; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D051381:Rats; D020239:Receptor Cross-Talk / Q000502:physiology*; D011965:Receptors, Glucocorticoid / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology; D014407:Tumor Cells, Cultured
chemical_list: D011965:Receptors, Glucocorticoid; C117909:SUMO2 protein, human; D025841:Small Ubiquitin-Related Modifier Proteins; D012694:Serine; D003907:Dexamethasone; D048031:JNK Mitogen-Activated Protein Kinases