Lysine Deacetylase Inhibitors Disrupt Glucocorticoid Receptor-Mediated Transcription and Circadian Rhythm
AuthorGriggs, Chanel Antoinette
AdvisorSmith, Catharine L.
MetadataShow full item record
PublisherThe University of Arizona.
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.
AbstractGlucocorticoids mediate their anti-inflammatory and immunosuppressive effects through activation of the glucocorticoid receptor (GR), a nuclear receptor, and subsequent effects on gene transcription. GR use lysine acetyltransferases (KATs, also known as histone acetyltransferases or HATs) and lysine deacetylases (KDACs, also known as histone deacetylases or HDACs) to regulate the transcription through acetylation and deacetylation of histones and nonhistone protein targets. Small molecule inhibitors of KDACs are approved for the clinical use of several diseases. Previously, we have shown that KDAC inhibition disrupts GR-mediated gene activation at several GR target genes and that disruption is mediated, in part, by loss of KDAC1 activity. In the current study, we examine the effect of KDAC inhibition on GC-induced gene activation and repression, discovering novel roles of Class I KDACs in regulation of the transcriptional cycle. In the first part of the study (Chapter 2), we show that KDAC inhibition through two structurally distinct KDAC inhibitors, prevents dexamethasone (Dex)-induced transcriptional repression in a gene-selective fashion. In addition, KDAC inhibition decreased the levels of H3K4Me2 through activation of lysine demethylase 1 (LSD1). These events prevent transcriptional repression at these gene promoters. However, this mechanism is specific for genes repressed by GC treatment, as LSD1 does not play a significant role in GR transactivation. In the second part of the study (Chapter 3), we discovered that KDAC inhibition disrupts multiple stages of active transcription in a gene-selective manner. Class I KDAC inhibition through valproic acid (VPA) did not affect the ability of activated GR to bind enhancer regions, nor did VPA treatment affect p300 recruitment to enhancer regions, suggesting that Class I KDACs are involved downstream of these initial enhancer activating steps. We then observed that VPA treatment disrupts RNA Polymerase II recruitment to enhancer and promoter regions in a gene-selective manner, further supporting the idea that Class I KDACs facilitate GR transactivation at different parts of the transcriptional cycle. In the last part of the study (Chapter 4), we examined the effect of VPA treatment on the transcription of several core circadian rhythm transcription factors. Using low dose glucocorticoid, we synchronized cultured fibroblast cells to a circadian oscillatory pattern. Whether VPA was added at the time of synchronization or 12 h later, we found that VPA disrupted the oscillatory expression of multiple genes encoding essential transcription factors that regulate circadian rhythm. Altogether, our study illustrates the disruption of the GR transcriptional cycle by VPA and other KDAC inhibitors, implicating these drugs as possible endocrine disrupters. This disruption is an unfortunate consequence of KDAC inhibition and the mechanism(s) behind must be fully elucidated as we continue to use these drugs to target various diseases.
Degree ProgramGraduate College
Pharmacology & Toxicology