Date of Degree
Access restricted until 07/13/2019
PhD (Doctor of Philosophy)
Anatomy and Cell Biology
Qi, Hank Heng
First Committee Member
Second Committee Member
Wallrath, Lori L.
Third Committee Member
Henry, Michael D.
Fourth Committee Member
Dupuy, Adam J.
Prostate cancer (PCa) is the most common cancer in American men. Although initial androgen deprivation therapy (ADT) confers a five year survival rate of 99%, the relapse of metastatic and drug resistant PCa (CRPC- Castration-Resistant PCa) continues to account for most deaths. How certain PCa cells develop into CRPC is the key question in the field. In addressing it, attention has focused on epigenetic factors that contribute to CRPC development. Herein we investigated the role and regulation of histone demethylase PHF8 during PCa neuroendocrine differentiation (NED) and progression into CRPC. We utilized bioinformatic analyses and biochemical approaches in PCa/CRPC cell line and mouse models to unravel the following results:
First, we discovered that PHF8 post-transcriptionally clusters with cell cycle genes during NED and into CRPC via an AR/MYC/miR-22 regulatory axis. We showed that this axis is dysregulated in CRPC cells to allow enhanced cell proliferation and resistance to the clinical AR antagonist drug Xtandi® (enzalutamide). Second, we revealed that PHF8 is necessary for hypoxia induced NED by demethylating repressive H3K9me2 and H3K27me2, above maintaining active H3K4me3 on select NED genes. Importantly, we unveiled that PHF8 sustains HIF1α expression in CRPC cells via a regulatory role associated with full length AR. Third, we recapitulated the role of PHF8 in vivo by excising its floxed allele in the prostate of TRAMP mice -Transgenic Adenocarcinoma of the Mouse Prostate. We observed that KO of Phf8 lowered tumor burden in part by sustaining Ezh2 expression during NED transition into CRPC.
In conclusion, our data implicates PHF8 in multiple oncogenic roles and regulations during PCa NED into CRPC. Our results lay a foundation for understanding the dynamics of histone modifying enzymes during PCa progression and hint at designing small molecule inhibitors against PHF8 as a novel CRPC therapeutic target.
Cancer afflicts individuals and their families emotionally and financially. Prostate cancer (PCa) in particular is the most common cancer affecting American men, but second most fatal after lung/bronchus cancer. Nevertheless, PCa has so far been subject to successful therapeutic interventions- the five year survival rate is almost 99%. However, within two to three years of treatment, some patients relapse with a more aggressive and therapy resistant form of PCa called castration-resistant prostate cancer (CRPC). How and why these patients develop CRPC is an enigma in the field.
Since PCa progression into CRPC does not contain many de novo DNA mutations, our research has instead focused on factors that change the packaging of DNA. In particular, we have looked at a protein called PHF8. We argued that PHF8 promotes progression of PCa into CRPC because it has been previously shown to control cell growth in other cancers. However, its exact role and regulation in PCa/CRPC remained largely unknown.
To test our argument, we used PCa cells and mice models to experiment on PHF8. We discovered that PHF8 is reduced during neuroendocrine differentiation (NED) - a process that appears to precede development of CRPC- but was increased in CRPC cells. We showed that its reduction during NED was enacted by other known oncogenic proteins in PCa i.e. AR and MYC. Then, we revealed that its increase in CRPC aided cell survival against therapy by controlling genes such as KDM3A, HIF1α and EZH2. Consequently, removal of PHF8 in CRPC cells and PCa mice lowered drug resistance and decreased tumor incidence respectively.
In conclusion, our data suggests that PHF8 is a potentially new target for CRPC therapy. This is significant in the field of PCa/CRPC research.
Castration-resistant prostate cancer (CRPCa), EZH2, HIF1, miR-22, Neuroendocrine differentiation (NED), PHF8
xx, 194 pages
Includes bibliographical references (pages 164-194).
Copyright © 2017 Peterson Kariuki Maina
Maina, Peterson Kariuki. "Novel oncogenic roles and regulations of histone demethylase PHF8 in prostate cancer." PhD (Doctor of Philosophy) thesis, University of Iowa, 2017.