REGULATION OF GLUCOCORTICOID RECEPTOR BY PHOSPHORYLATION
Principal Investigator: Michael Garabedian
Abstract: The overall objectives of this proposal are to characterize the molecular mechanisms by which phosphorylation regulates glucocorticoid receptor (GR) activity. GR is a hormone-dependent transcription factor expressed in virtually all tissues, yet it displays a remarkable capacity to regulate genes in a cell type- specific manner. Although glucocorticoids act as the primary signal in activating GR's transcriptional regulatory functions, GR-mediated transcriptional activity is also regulated by phosphorylation. The amino terminus of GR contains a transcriptional activation domain that is phosphorylated at four major sites in cultured mammalian cells. Several kinases have been identified that phosphorylate GR in vitro at the identified sites. Of these, the cyclin-dependent kinases (Cdks) phosphorylate serine 232 (S232) and serine (S224), while c-Jun N- terminal kinase (JNK) phosphorylates serine 246 (S246) and glycogen synthase kinase-3 (GSK3) phosphorylates threonine 171 (T171). Phosphorylation of these sites is important for GR function: serine to alanine mutations of S224 and S232 decrease GR transcriptional activation, whereas alanine mutations of T171 and S246 increase GR transcriptional activation. Thus, GR- mediated transcriptional activity is regulated both positively and negatively by phosphorylation. We propose that phosphorylation by multiple protein kinases enables GR to respond to diverse extracellular signals. This ability to integrate multiple signals in the form of phosphorylation permits a flexibility in GR action that, in conjunction with the steroid ligands, may be crucial in coordinating the cell type specific actions of GR. We further hypothesize that phosphorylation regulates GR's interaction with proteins involved in transcriptional regulation. This hypothesis will be addressed by expressing activators or inhibitors of Cdk, JNK and GSK3 in cultured mammalian cells in transient transfection assays designed to monitor GR-dependent transcriptional regulation. In addition, we will identify and characterize proteins that interact with the GR N-terminal transcriptional activation domain in a phosphorylation-dependent manner using a protein interaction screen in yeast. Gaining a mechanistic understanding of the communication between multiple signaling pathways, as realized through GR and its regulatory kinases, is fundamental to understanding the mechanism of GR-regulated gene expression and may reveal likely points of intervention to be exploited in the development of new therapies for glucocorticoid-resistant malignancies, such as breast cancer and acute lymphoblastic leukemia.
Funding Period: 1999-03-01 - 2005-01-31
more information: NIH RePORT
- Ligand structural motifs can decouple glucocorticoid receptor transcriptional activation from target promoter occupancyRaymond D Blind
Department of Pharmacology, New York University School of Medicine, New York, NY 10016, USA
Biochem Biophys Res Commun 420:839-44. 2012..Thus, although steroids that bind GR with high affinity can induce GR and p300 occupancy of target promoters, they may not induce a conformation of GR capable of activating transcription...
- Expression and regulation of glucocorticoid receptor in human placental villous fibroblastsMen Jean Lee
Department of Obstetrics and Gynecology, New York University School of Medicine, New York, NY 10016, USA
Endocrinology 146:4619-26. 2005..Such cell type-specific differences in GR protein expression and phosphorylation may provide the means of differentially regulating the GC response among the cells of the human placenta...
- Modulation of glucocorticoid receptor phosphorylation and transcriptional activity by a C-terminal-associated protein phosphataseZhen Wang
Department of Microbiology, New York University Cancer Institute, New York University School of Medicine, 550 First Avenue, New York, New York 10016, USA
Mol Endocrinol 21:625-34. 2007....
- Differential recruitment of glucocorticoid receptor phospho-isoforms to glucocorticoid-induced genesRaymond D Blind
Department of Microbiology, NYU Cancer Institute, NYU School of Medicine, 550 First Avenue, New York, NY 10016, United States
J Steroid Biochem Mol Biol 109:150-7. 2008..Our findings indicate that GR phospho-isoforms selectively occupy GR target genes, and suggests gene specific requirements for GR phosphorylation in receptor-dependent transcriptional activation...
- Glucocorticoid receptor phosphorylation differentially affects target gene expressionWeiwei Chen
Department of Pharmacology, and the NYU Cancer Institute, NYU School of Medicine, 550 First Avenue, New York, New York 10016, USA
Mol Endocrinol 22:1754-66. 2008..Furthermore, the effect of GR S211 phosphorylation is gene specific and, in some cases, dependent upon the amount of activated receptor...