Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Mary Kay H. Pflum

Abstract

Aberrant expression of histone deacetylase 1 (HDAC1) is implicated in multiple diseases, including cancer. As a consequence, HDAC1 has emerged as an important therapeutic target for drug development. HDAC1 regulates key cellular processes, such as cell proliferation, apoptosis, and cell survival, by deacetylating both histone and non-histone substrates. Due to the lack of simple tools to identify physiological substrates of HDAC1, the full spectrum of HDAC1 activities in the cell remains unclear. Here, we employed a substrate trapping strategy to identify cellular substrates of HDAC1. Using this approach, we identified mitosis-related protein Eg5 as a substrate. HDAC1 colocalizes with Eg5 during mitosis, suggesting a role for HDAC1 in the mitotic defects observed with HDAC inhibitor drugs.

By extending substrate trapping strategy to HEK293 cells, we identified Lysine Specific Demethylase 1 (LSD1) as an HDAC1 substrate. Significantly, LSD1 is overexpressed in multiple cancers and has emerged as a potential anti-cancer drug target. LSD1 is typically found in association with another epigenetic enzyme, histone deacetylase (HDAC). HDAC and LSD1 inhibitor compounds have been tested as combination anti-cancer agents. However, the functional link between LSD1 and HDAC has yet to be understood in detail. Here we uncovered that HDAC1 mediated deacetylation of LSD1 at K374 in the substrate binding lobe, which affected the histone 3 binding and gene expression activity of LSD1. The mechanistic link between HDAC1 and LSD1 established here suggests that HDAC inhibitors influence LSD1 activity, which will ultimately guide drug design targeting epigenetic enzymes. Discovery of novel substrates using trapping mutants will reveal the full activities of HDAC1 in both physiological and pathological conditions, which will lead to a better understanding of HDAC inhibitor mechanism of action.

My second project focused on studying the effect of Single nucleotide polymorphisms (SNPs) of HDAC1. HDAC1 is upregulated in multiple diseases, and has emerged as an important therapeutic target for drug development. SNPs in multiple genes are often linked to the diseases, such as cancer. Here, we used the Hypothesis driven SNP search (HyDn-SNP-S) program to identify a HDAC1 SNP-F437C. The presence of SNP-F437C on HDAC1 affected acetylation at K432 and phosphorylation at S393, which ultimately altered enzymatic activity. These studies shed insights into the altered posttranslational modifications caused by HDAC1 exonic SNP. The study also revealed the significance of studying SNPs of HDAC in understanding the mechanisms leading to HDAC deregulation in cancer.

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