Author ORCID Identifier
Date Available
12-15-2025
Year of Publication
2023
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Medicine
Department/School/Program
Toxicology and Cancer Biology
Advisor
Dr. Qiou Wei
Abstract
Prostate cancer is the most common and second leading cause of cancer death in men. Prevailing theories state that inflammation may drive prostate carcinogenesis via oxidative stress and the generation of reactive oxygen species (ROS) that induce somatic mutagenesis. Since high proliferating cells or cancer cells exhibit aberrant metabolism to satisfy the needs of energy for rapid cell proliferation, they also generate high levels of ROS which stimulates the expression of cellular antioxidants to overcome the dysregulation of redox homeostasis through the regulation of redox-sensitive transcription factors. Among different antioxidants, peroxiredoxin (Prx) family proteins are the highly conserved and mostly abundant family of peroxidases that scavenge hydrogen peroxide as well as mediate redox signaling under both physiological and pathological conditions. Peroxiredoxin IV (Prx4) is one of Prx family members that mainly localizes in the endoplasmic reticulum (ER), but can also be found extracellular space. But, the absence of mechanistic input and experimental evidence compromise the understanding of role and significance of Prx4 in the pathogenesis of human diseases, especially in prostate cancer. In this study, our goal is to evaluate the expression of Prx4 in human prostate cancer, to study whether and how Prx4 contributes to prostate cancer malignancy, as well as to understand its secretion mechanism. Prx4 is highly expressed in patient specimens of prostate cancer as well as established prostate cancer cell lines, and its levels can be further stimulated through the activation of androgen receptor (AR) signaling. To study the mechanism of Prx4 in regulating prostate cancer malignancy, we used two different strategies to deplete the endogenous Prx4, including short hairpin RNA and CRISPR/Cas9 techniques. Compared with control cells, Prx4-depleted cells show delayed cell cycle progression, and reduced rate of cell proliferation. We found that loss of Prx4 results in insufficient phosphorylation of both Akt and its downstream kinase GSK3α/β via Proteome profiler phospho-kinase arrays. Moreover, Prx4-depleted cells are more sensitive to ionizing radiation with the observation of compromised ability to scavenge ROS and increased accumulation of DNA damage. We also found loss of Prx4 shows reduced the population of migrating cells and stem cells, ability of migration and invasion. By performing RNA sequencing and Gene Set Enrichment Analysis, we found depletion of Prx4 reduces the expression of NF-κB2, and inhibits Epithelial-Mesenchymal transition (EMT). All the conclusions were further confirmed using xenograft mouse model. Because of its important role in prostate cancer growth and metastasis, we further investigate the secretion mechanism of Prx4. We first confirmed the secretion capacity of Prx4 via western blot analysis of human/mouse plasma and cell-cultured medium. By manipulating the N-terminal hydrophobic region, we further confirmed that Prx4 has its signal peptide which drives its secretion. Through the use of inhibitors, downregulation of key regulatory genes, and fluorescence imaging, we targeted classical and unconventional protein secretion pathways and investigated the colocalization of Prx4 with different subcellular organelles. Our results revealed that Prx4 secretion depends on the Endo-lysosomal mediated Type III protein secretion pathway, with Prx4 being present in exomeres or distinct nanoparticles (DNPs) rather than EVs. The secreted Prx4 retained its antioxidant function with reduced cysteine residues. Moreover, we observed upregulated Prx4 expression in all three types of human cancers, with varying secretion levels among different cell lines. We also observed the accumulation of Prx4 in mouse plasma in both PTEN/Pb-Cre transgenic prostate cancer mouse model as well as AOM/DSS induced colorectal cancer mouse model. In conclusion, our results show the importance and function of Prx4 in contributing to prostate cancer growth, metastasis, and stemness via different signaling pathways. Our study indicates that targeting Prx4 may be utilized as a potential strategy to control tumor growth and metastasis in prostate cancer patients. The absence of a dedicated inhibitor holds its utilization to improve current therapies. Therefore, strategies targeting Prx4 are urgent to develop and use to improve current clinical therapeutic treatments in prostate cancer. Aside as a therapeutic target, Prx4 holds its potential as a biomarker whether alone or combined with PSA to help early diagnosis and monitor prostate cancer relapse.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2023.423
Recommended Citation
Ding, Na, "ELUCIDATING THE FUNCTIONAL IMPORTANCE OF PEROXIREDOXIN IV IN PROSTATE CANCER AND ITS SECRETION MECHANISM" (2023). Theses and Dissertations--Toxicology and Cancer Biology. 51.
https://uknowledge.uky.edu/toxicology_etds/51
