Insights into the biochemical life cycle of the vitamin D receptor: Protein and DNA interactions that transduce the signal for gene expression

Persistent Link:
http://hdl.handle.net/10150/280172
Title:
Insights into the biochemical life cycle of the vitamin D receptor: Protein and DNA interactions that transduce the signal for gene expression
Author:
Encinas, Carlos
Issue Date:
2002
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The biological actions of 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) are mediated by the nuclear vitamin D receptor (VDR), which functions as a ligand-dependent transcriptional regulator. We have developed a six-stage molecular model summarizing the VDR transcriptional activation-life cycle, and tested this model using a variety of experimental approaches, including pull-down assays with GST-fusion proteins, as well as assays of the functional activity of VDR and its putative coactivators in transiently transfected mammalian cells. The six stages of the VDR life cycle are: (1) unoccupied VDR binds to a transcriptional corepressor which serves as a chaperone, maintaining the main protein players in close contact in an inactive complex; (2) VDR becomes occupied by 1,25(OH)₂D₃ ligand, enabling the receptor to heterodimerize strongly with a retinoid X receptor (RXR), leading to high affinity DNA binding and recruitment of coactivators with histone acetyl transferase (HAT) activity; (3) coactivator HAT activity promotes chromatin remodeling, rendering the gene promoter free to interact with the transcription preinitiation complex (PIC); (4) dissociation of VDR from the HAT coactivators, followed by association of a second set of coactivators that promote formation of the preinitiation complex (PIC); (5) transcriptional recycling of the liganded receptor and heteropartner to initiate additional rounds of transcription; and (6) ubiquitination and eventual degradation of VDR. Phosphorylation of VDR may influence all six stages. A testable conclusion from our model is that the role of the 1,25(OH)₂D₃ hormonal ligand would be primarily in the transition from stage 1 to stage 2, but the continued presence of 1,25(OH)₂D₃ appears to be necessary also for the progression from stages 3 through 6 to VDR degradation, or alternatively for recycling via stage 5. This characterization of the macromolecular cofactors that transduce the signal of the 1,25(OH)₂D₃ hormone to promote gene expression in vitamin D target tissues should add to our understanding of endocrine control of bone mineral remodeling and of epithelial cell differentiation. The present work also identifies new protein players that are candidates for mutation or dysregulation in the pathophysiology of vitamin D resistant bone disorders (osteoporosis), and in hyperproliferative diseases of vitamin D regulated epithelial tissues such as skin.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Biology, Molecular.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Molecular and Cellular Biology
Degree Grantor:
University of Arizona
Advisor:
Haussler, Mark R.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleInsights into the biochemical life cycle of the vitamin D receptor: Protein and DNA interactions that transduce the signal for gene expressionen_US
dc.creatorEncinas, Carlosen_US
dc.contributor.authorEncinas, Carlosen_US
dc.date.issued2002en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe biological actions of 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) are mediated by the nuclear vitamin D receptor (VDR), which functions as a ligand-dependent transcriptional regulator. We have developed a six-stage molecular model summarizing the VDR transcriptional activation-life cycle, and tested this model using a variety of experimental approaches, including pull-down assays with GST-fusion proteins, as well as assays of the functional activity of VDR and its putative coactivators in transiently transfected mammalian cells. The six stages of the VDR life cycle are: (1) unoccupied VDR binds to a transcriptional corepressor which serves as a chaperone, maintaining the main protein players in close contact in an inactive complex; (2) VDR becomes occupied by 1,25(OH)₂D₃ ligand, enabling the receptor to heterodimerize strongly with a retinoid X receptor (RXR), leading to high affinity DNA binding and recruitment of coactivators with histone acetyl transferase (HAT) activity; (3) coactivator HAT activity promotes chromatin remodeling, rendering the gene promoter free to interact with the transcription preinitiation complex (PIC); (4) dissociation of VDR from the HAT coactivators, followed by association of a second set of coactivators that promote formation of the preinitiation complex (PIC); (5) transcriptional recycling of the liganded receptor and heteropartner to initiate additional rounds of transcription; and (6) ubiquitination and eventual degradation of VDR. Phosphorylation of VDR may influence all six stages. A testable conclusion from our model is that the role of the 1,25(OH)₂D₃ hormonal ligand would be primarily in the transition from stage 1 to stage 2, but the continued presence of 1,25(OH)₂D₃ appears to be necessary also for the progression from stages 3 through 6 to VDR degradation, or alternatively for recycling via stage 5. This characterization of the macromolecular cofactors that transduce the signal of the 1,25(OH)₂D₃ hormone to promote gene expression in vitamin D target tissues should add to our understanding of endocrine control of bone mineral remodeling and of epithelial cell differentiation. The present work also identifies new protein players that are candidates for mutation or dysregulation in the pathophysiology of vitamin D resistant bone disorders (osteoporosis), and in hyperproliferative diseases of vitamin D regulated epithelial tissues such as skin.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBiology, Molecular.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineMolecular and Cellular Biologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorHaussler, Mark R.en_US
dc.identifier.proquest3073217en_US
dc.identifier.bibrecord.b43428083en_US
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