U-Ging Lo

The Role and Mechanism of Epithelial-to-Mesenchymal Transition in Prostate Cancer Progression

In prostate cancer (PCa), similar to many other cancers, distant organ metastasis symbolizes the beginning of the end disease, which eventually leads to cancer death. Many mechanisms have been identified in this process that can be rationalized into targeted therapy. Among them, epithelial-to-mesenchymal transition (EMT) is originally characterized as a critical step for cell trans-differentiation during embryo development and now recognized in promoting cancer cells invasiveness because of high mobility and migratory abilities of mesenchymal cells once converted from carcinoma cells. Nevertheless, the underlying pathways leading to EMT appear to be very diverse in different cancer types, which certainly represent a challenge for developing effective intervention. In this article, we have carefully reviewed the key factors involved in EMT of PCa with clinical correlation in hope to facilitate the development of new therapeutic strategy that is expected to reduce the disease mortality.

Impact of cholesterol on disease progression

Cholesterol-rich microdomains (also called lipid rafts), where platforms for signaling are provided and thought to be associated with microbe-induced pathogenesis and lead to cancer progression. After treatment of cells with cholesterol disrupting or usurping agents, raft-associated proteins and lipids can be dissociated, and this renders the cell structure nonfunctional and therefore mitigates disease severity. This review focuses on the role of cholesterol in disease progression including cancer development and infectious diseases. Understanding the molecular mechanisms of cholesterol in these diseases may provide insight into the development of novel strategies for controlling these diseases in clinical scenarios.

The role of microRNAs in prostate cancer progression

Prostate cancer (PCa) is the most common male malignancy and the second highest cause of cancer-related mortality in United States. MicroRNAs (miRNAs) are small non-coding RNAs that represent a new mechanism to regulate mRNA post-transcriptionally. It is involved in diverse physiological and pathophysiological process. Dysregulation of miRNAs has been associated with the multistep progression of PCa from prostatic intraepithelial neoplasia (PIN), localized adenocarcinoma to metastatic castration-resistance PCa (CRPC). Identification of unique miRNA could provide new biomarkers for PCa and develop into therapeutic strategies. In this review, we will summarize a broad spectrum of both tumor suppressive and oncogenic miRNAs, and their mechanisms contribute to prostate carcinogenesis.

Sensitization of Radioresistant Prostate Cancer Cells by Resveratrol Isolated from Arachis hypogaea Stems

Resveratrol (RV, 3,4ʹ,5-trihydroxystilbene) is naturally produced by a wide variety of plants including grapes and peanuts (Arachis hypogaea). However, the yield of RV from peanut stem and its potential radiosensitizing effects in prostate cancer (PCa) have not been well investigated. In this study, we characterized RV in peanut stem extract (PSE) for the first time and showed that both RV and PSE dose-dependently induced cell death in DOC-2/DAB2 interactive protein (DAB2IP)-deficient PCa cells with the radioresistant phenotype. Furthermore, the combination of radiation with either RV or PSE induced the death of radioresistant PCa cells through delayed repair of radiation-induced DNA double-strand break (DSB) and prolonged G2/M arrest, which induced apoptosis. The administration of RV and PSE effectively enhanced radiation therapy in the shDAB2IP PCa xenograft mouse model. These results demonstrate the promising synergistic effect of RV and PSE combined with radiation in the treatment of radioresistant PCa.

Molecular mechanisms and potential clinical applications of Campylobacter jejuni cytolethal distending toxin

Cytolethal distending toxin (CDT), a genotoxin produced by Campylobacter jejuni, is composed of three subunits: CdtA, CdtB, and CdtC. CdtB is a DNase that causes DNA double-strand breaks (DSB) in the nucleus resulting in cell cycle arrest at the G2/M stage and apoptosis. CdtA and CdtC bind to cholesterol-rich microdomains on the cytoplasmic membrane, a process required for the delivery of CdtB to cells. Although a unique motif associated with cholesterol-binding activity has been identified in other pathogens, the mechanism underlying the interaction between the CdtA and CdtC subunits and membrane cholesterol remains unclear. Also, the processes of cell uptake and delivery of CdtB in host cells and the translocation of CdtB into the nucleus are only partially understood. In this review, we focus on the underlying relationship among CDT, membrane cholesterol, and the intracellular trafficking pathway as a unique mechanism for C. jejuni-induced pathogenesis. Moreover, we discuss the clinical aspects of a possible therapeutic application of CDT in cancer therapy. Understanding the molecular mechanism of CDT-host interactions may provide insights into novel strategies to control C. jejuni infection and the development of potential clinical applications of CDT.

Developing new targeting strategy for androgen receptor variants in castration resistant prostate cancer

The presence of androgen receptor variant 7 (AR‐V7) variants becomes a significant hallmark of castration‐resistant prostate cancer (CRPC) relapsed from hormonal therapy and is associated with poor survival of CRPC patients because of lacking a ligand‐binding domain. Currently, it still lacks an effective agent to target AR‐V7 or AR‐Vs in general. Here, we showed that a novel class of agents (thailanstatins, TSTs and spliceostatin A analogs) can significantly suppress the expression of AR‐V7 mRNA and protein but in a less extent on the full‐length AR expression. Mechanistically, TST‐D is able to inhibit AR‐V7 gene splicing by interfering the interaction between U2AF65 and SAP155 and preventing them from binding to polypyrimidine tract located between the branch point and the 3′ splice site. In vivo, TST‐D exhibits a potent tumor inhibitory effect on human CRPC xenografts leading to cell apoptosis. The machinery associated with AR gene splicing in CRPC is a potential target for drugs. Based on their potency in the suppression of AR‐V7 responsible for the growth/survival of CRPC, TSTs representing a new class of anti‐AR‐V agents warrant further development into clinical application.

Cytolethal Distending Toxin Enhances Radiosensitivity in Prostate Cancer Cells by Regulating Autophagy

Cytolethal distending toxin (CDT) produced by Campylobacter jejuni contains three subunits: CdtA, CdtB, and CdtC. Among these three toxin subunits, CdtB is the toxic moiety of CDT with DNase I activity, resulting in DNA double-strand breaks (DSB) and, consequently, cell cycle arrest at the G2/M stage and apoptosis. Radiation therapy is an effective modality for the treatment of localized prostate cancer (PCa). However, patients often develop radioresistance. Owing to its particular biochemical properties, we previously employed CdtB as a therapeutic agent for sensitizing radioresistant PCa cells to ionizing radiation (IR). In this study, we further demonstrated that CDT suppresses the IR-induced autophagy pathway in PCa cells by attenuating c-Myc expression and therefore sensitizes PCa cells to radiation. We further showed that CDT prevents the formation of autophagosomes via decreased high-mobility group box 1 (HMGB1) expression and the inhibition of acidic vesicular organelle (AVO) formation, which are associated with enhanced radiosensitivity in PCa cells. The results of this study reveal the detailed mechanism of CDT for the treatment of radioresistant PCa.

The evolving landscape of prostate cancer stem cell: Therapeutic implications and future challenges

Prostate cancer (PCa) is the most common cause of malignancy in males and the second leading cause of cancer mortality in United States. Current treatments for PCa include surgery, radiotherapy, and androgen-deprivation therapy. Eventually, PCa relapses to an advanced castration-resistant PCa (CRPC) that becomes a systematic disease and incurable. Therefore, identifying cellular components and molecular mechanisms that drive aggressive PCa at early stage is critical for disease prognosis and therapeutic intervention. One potential strategy for aggressive PCa is to target cancer stem cells (CSCs) that are identified by several unique characteristics such as immortal, self-renewal, and pluripotency. Also, CSC is believed to be a major factor contributing to resistance to radiotherapy and conventional chemotherapies. Moreover, CSCs are thought to be the critical cause of metastasis, tumor recurrence and cancer-related death of multiple cancer types, including PCa. In this review, we discuss recent progress made in understanding prostate cancer stem cells (PCSCs). We focus on the therapeutic strategies aimed at targeting specific surface markers of CSCs, the key signaling pathways in the maintenance of self-renewal capacity of CSCs, ATP-binding cassette (ABC) transporters that mediate the drug-resistance of CSCs, dysregulated microRNAs expression profiles in CSCs, and immunotherapeutic strategies developed against PCSCs surface markers.

Abstract 2873: Identification of a new mechanism of microRNA turnover from miR-106a-363 cluster leading to epithelial-to-mesenchymal transition in prostate cancer

Background: Prostate cancer (PCa) is the second leading cause of cancer mortality in US. The majority of PCa mortality is due to the recurrent of metastatic castration resistant PCa. The acquisition of epithelial-to-mesenchymal transition (EMT) signifies PCa metastasis. In particular, altered microRNAs (miRNAs) expression is closely associated with PCa progression from prostatic intraepithelial neoplasia to metastatic adenocarcinoma. miRNAs are small noncoding RNAs regulating approximately 60% protein-coding genes by post-transcriptional suppression or translational inhibition. miRNA gene expression at post-transcriptional level becomes more complicated when multiple miRNAs derived from the same cluster generate a polycistronic primary transcript, and each individual miRNA displays different expression profile and functional role. miRNA-363 (miR-363) belongs to the miR-106a-363 cluster containing miR-106a, miR-18b, miR-20b, miR-19b-2, miR-92a-2 and miR-363. Unlike the other five miRNAs which are closely resemble to the oncogenic miR-17-92 cluster in their seed sequence and function, miR-363 has been implicated to play a tumor suppressor role in several types of cancer, indicating a different regulatory mechanism of miR-363 from the miR-106a-363 cluster. Interferon-induced tetratricopeptide repeat 5 (IFIT5) is first characterized as a viral RNA binding protein and has been shown to directly bind to cellular tRNA, which partially shared a structural similarity with precursor miRNAs (pre-miRNAs). However, until now, there is no report indicating the RNA recognition role of IFIT5 in miRNA biogenesis machinery. Results: In the present study, miR-363 was clearly identified as a tumor suppressor miRNA by inhibiting EMT in PCa cells via targeting slug/SNAI2. More importantly, we have demonstrated, for the first time, that IFIT5 is able to recognize a unique structure at the 5′ end of precursor miR-363, which facilitates pre-miR-363 degradation by the recruitment of a 5′-3′exoribonuclease, XRN1. Meanwhile, we have also shown that the significant elevation of IFIT5 is detected in several PCa cells undergone EMT leading to highly metastatic potential. In addition, an inverse correlation between miR-363 and IFIT5 mRNA level was found in human PCa specimens. Conclusion: We unveil IFIT5 complex as a new post-transcriptional regulatory mechanism specific for miR-363 turnover at the precursor stage, which determines the stability and unique functional role of miR-363 distinct from other oncogenic miRNA members in the miR-106a-363 cluster. Overall, this study provides an insight of miRNA biogenesis machinery in cancer metastasis and new strategies of therapeutic intervention of PCa. Citation Format: U-Ging Lo, Rey-Chen Pong, Diane Yang, Jiancheng Zhou, Leah Gandee, Shu-Fen Tseng, Jer-Tsong Hsieh. Identification of a new mechanism of microRNA turnover from miR-106a-363 cluster leading to epithelial-to-mesenchymal transition in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2873. doi:10.1158/1538-7445.AM2015-2873

IFN-γ induces epithelial-to-mesenchymal transition of cancer cells via an unique microRNA processing

Interferon-γ (IFNγ) is a potent cytokine in modulating tumor immunity and tumoricidal effects. We demonstrate a new function of IFNγ in inducing epithelial-to-mesenchymal transition (EMT) in normal and cancer cells from different cell types. IFNγ activates JAK-STAT signaling pathway leading to the transcription of IFN-stimulated genes (ISGs), such as interferon-induced tetratricopeptide repeat 5 (IFIT5). We unveil a new function of IFIT5 complex in degrading precursor microRNAs (pre-miRNA) that include pre-miR-363 from the miR-106a-363 cluster, as well as pre-miR-101 and pre-miR-128 with a similar 5’-end structure with pre-miR-363. Noticeably, these suppressive miRNAs have similar functions by targeting EMT transcription factors in prostate cancer (PCa) cells. We further demonstrated that IFIT5 plays a critical role in IFNγ-induced cell invasiveness in vitro and lung metastasis in vivo. Clinically, IFIT5 is highly elevated in high-grade PCa and its expression inversely correlates with these suppressive miRNAs. Altogether, this study unveils pro-tumorigenic role of the IFN pathway via a new mechanism of action, which certainly raises concern about its clinical application.