Po-Chen Chu - Academia.edu (original) (raw)

Papers by Po-Chen Chu

International Journal of Molecular Sciences

Cancer stem cells (CSCs), or tumor-initiating cells, are a small subset of cancer cells with the ... more Cancer stem cells (CSCs), or tumor-initiating cells, are a small subset of cancer cells with the capacity for self-renewal and differentiation, which have been shown to drive tumor initiation, progression, and metastasis in many types of cancer. Moreover, therapeutic regimens, such as cisplatin and radiation were reported to induce the enrichment of CSCs, thereby conferring chemoresistance on cancer cells. Therefore, therapeutic targeting of CSCs represents a clinical challenge that needs to be addressed to improve patient outcome. In this context, the effectiveness of pan or class-I histone deacetylase (HDAC) inhibitors in suppressing the CSC population is especially noteworthy in light of the new paradigm of combination therapy. Evidence suggests that this anti-CSC activity is associated with the ability of HDAC inhibitors to target multiple signaling pathways at different molecular levels. Beyond chromatin remodeling via histone acetylation, HDAC inhibitors can also block key signaling pathways pertinent to CSC maintenance. Especially noteworthy is the ability of different HDAC isoforms to regulate the protein stability and/or activity of a series of epithelial-mesenchymal transition (EMT)-inducing transcription factors, including HIF-1α, Stat3, Notch1, β-catenin, NF-κB, and c-Jun, each of which plays a critical role in regulating CSCs. From the translational perspective, these mechanistic links constitute a rationale to develop isoform-selective HDAC inhibitors as anti-CSC agents. Thus, this review aims to provide an overview on the roles of HDAC isoforms in maintaining CSC homeostasis via distinct signaling pathways independent of histone acetylation.

Oncogene, Jan 21, 2018

Although the role of insulin-like growth factor-I receptor (IGF-IR) in promoting colorectal liver... more Although the role of insulin-like growth factor-I receptor (IGF-IR) in promoting colorectal liver metastasis is known, the mechanism by which IGF-IR is upregulated in colorectal cancer (CRC) is not defined. In this study, we obtained evidence that mutant KRAS transcriptionally activates IGF-IR gene expression through Y-box-binding protein (YB)-1 upregulation via a novel MEK-Sp1-DNMT1-miR-137 pathway in CRC cells. The mechanistic link between the tumor suppressive miR-137 and the translational regulation of YB-1 is intriguing because epigenetic silencing of miR-137 represents an early event in colorectal carcinogenesis due to promoter hypermethylation. This proposed signaling axis was further verified by the immunohistochemical evaluations of liver metastases from a cohort of 46 KRAS mutant CRC patients, which showed a significant correlation in the expression levels among Sp1, miR-137, YB-1, and IGF-1R. Moreover, suppression of the expression of YB-1 and IGF-IR via genetic knockdown...

Scientific Reports

In this study, we interrogated the mechanism by which the immunosuppressant FTY720 mediates antic... more In this study, we interrogated the mechanism by which the immunosuppressant FTY720 mediates anticancer effects in oral squamous cell carcinoma (OSCC) cells. FTY720 differentially suppressed the viability of the OSCC cell lines SCC4, SCC25, and SCC2095 with IC 50 values of 6.1, 6.3, and 4.5 μM, respectively. This antiproliferative effect was attributable to the ability of FTY720 to induce caspase-dependent apoptosis. Mechanistic evidence suggests that FTY720-induced apoptosis was associated with its ability to inhibit Akt-NF-κB signaling, to facilitate the proteasomal degradation of the antiapoptotic protein Mcl-1, and to increase reactive oxygen species (ROS) generation. Both overexpression of Mcl-1 and inhibition of ROS partially protected cells from FTY720-induced caspase-9 activation, PARP cleavage and cytotoxicity. In addition, FTY720 induced autophagy in OSCC cells, as manifested by LC3B-II conversion, decreased p62 expression, and accumulation of autophagosomes. Inhibition of autophagy by bafilomycin A1 protected cells from FTY720-induced apoptosis. Together, these findings suggest an intricate interplay between autophagy and apoptosis in mediating the tumorsuppressive effect in OSCC cells, which underlies the translational potential of FTY720 in fostering new therapeutic strategies for OSCC. Oral squamous cell carcinoma (OSCC) is the most common malignant tumor of the head and neck, and the incidence is increasing worldwide 1. OSCC is associated with multiple risk factors, among which tobacco use, alcohol, and betel quid chewing are most noteworthy. In response, surgery, chemotherapy, radiotherapy, and molecular targeted therapy have been used for the treatment of OSCC. However, drug resistance, either intrinsic or acquired, poses a major obstacle for OSCC therapy in light of limited treatment modalities, which highlights the urgency to develop novel strategies for OSCC treatment. FTY720 is a synthetic analogue of ISP-1 (myriocon), a fungal metabolite found in traditional Chinese herbal medicine 2. Originally, FTY720 was developed as an immunosuppressant because of its activity, after being converted to FTY720-phosphate, to promote the migration and homing of lymphocytes through interaction with the sphingosine-1-phosphate (S1P) receptors 3-5. Recently, the antitumor activity of FTY720 has been the focus of many investigations. FTY720 has also been shown to induce apoptosis in many different human cancer cell lines, including those of breast, prostate, lung, ovarian, brain, and hematopoietic malignancies 6-10. Interestingly, the antitumor activity of FTY720 is not related to interaction with S1P receptor (S1PR) 11. Several S1PR-independent

Oncotarget, 2017

Pancreatic cancer is an aggressive malignancy that is the fourth leading cause of death worldwide... more Pancreatic cancer is an aggressive malignancy that is the fourth leading cause of death worldwide. Since there is a dire need for novel and effective therapies to improve the poor survival rates of advanced pancreatic cancer patients, we analyzed the antitumor effects of OSU-A9, an indole-3-carbinol derivative, on pancreatic cancer cell lines in vitro and in vivo. OSU-A9 exhibited a stronger antitumor effect than gemcitabine on two pancreatic cancer cell lines, including gemcitabine-resistant PANC-1 cells. OSU-A9 treatment induced apoptosis, the down-regulation of Akt phosphorylation, up-regulation of p38 phosphorylation and decreased phosphorylation of JAK and STAT3. Cell migration and invasiveness assays showed that OSU-A9 reduced cancer cell aggressiveness and inhibited BxPC-3 xenograft growth in nude mice. These results suggest that OSU-A9 modulates the p38-JAK-STAT3 signaling module, thereby inducing cytotoxicity in pancreatic cancer cells. Continued evaluation of OSU-A9 as a potential therapeutic agent for pancreatic cancer thus appears warrented.

Small GTPases, 2016

Although oncogenic KRAS represents a therapeutically relevant target in pancreatic cancer, it is ... more Although oncogenic KRAS represents a therapeutically relevant target in pancreatic cancer, it is deemed &amp;amp;amp;quot;non-druggable&amp;amp;amp;quot; because of the intrinsic difficulty in designing direct inhibitors of KRAS. Our recent work demonstrated a KRAS-integrin-linked kinase (ILK) regulatory feedback loop that allows pancreatic cancer cells to regulate KRAS expression and to interact with the tumor microenvironment to promote aggressive phenotype. KRAS induces E2F1-mediated transcriptional activation of ILK expression, and ILK, in turn, controls KRAS expression via hnRNPA1, which binds and destabilizes the G-quadruplex in the KRAS promoter. Moreover, ILK inhibition blocked KRAS-driven EMT and growth factor-stimulated KRAS expression. This regulatory loop, however, was not noted in KRAS mutant colorectal and lung cancer cells examined as knockdown of KRAS or ILK did not affect each other&amp;amp;amp;#39;s expression, suggesting that this KRAS-ILK feedback regulation is specific for pancreatic cancer. In sum, this regulatory loop provides a strong mechanistic rationale for suppressing oncogenic KRAS signaling through targeting ILK, and this creating a potential new therapeutic strategy for pancreatic cancer.

PloS one, 2016

Colorectal cancer is the most common form of cancer in the world, and the five-year survival rate... more Colorectal cancer is the most common form of cancer in the world, and the five-year survival rate is estimated to be almost 90% in the early stages. Therefore, the identification of potential biomarkers to assess the prognosis of early stage colorectal cancer patients is critical for further clinical treatment. Dysregulated tyrosine phosphorylation has been found in several diseases that play a significant regulator of signaling in cellular pathways. In this study, this strategy was used to characterize the tyrosine phosphoproteome of colorectal cell lines with different progression abilities (SW480 and SW620). We identified a total of 280 phosphotyrosine (pTyr) peptides comprising 287 pTyr sites from 261 proteins. Label-free quantitative analysis revealed the differential level of a total of 103 pTyr peptides between SW480 and SW620 cells. We showed that cyclin-dependent kinase I (CDK1) pTyr15 level in SW480 cells was 3.3-fold greater than in SW620 cells, and these data corresponde...

Scientific reports, Jun 9, 2016

Phenothiazines (PTZs) have been used for the antipsychotic drugs for centuries. However, some of ... more Phenothiazines (PTZs) have been used for the antipsychotic drugs for centuries. However, some of these PTZs have been reported to exhibit antitumor effects by targeting various signaling pathways in vitro and in vivo. Thus, this study was aimed at exploiting trifluoperazine, one of PTZs, to develop potent antitumor agents. This effort culminated in A4 [10-(3-(piperazin-1-yl)propyl)-2-(trifluoromethyl)-10H-phenothiazine] which exhibited multi-fold higher apoptosis-inducing activity than the parent compound in oral cancer cells. Compared to trifluoperazine, A4 demonstrated similar regulation on the phosphorylation or expression of multiple molecular targets including Akt, p38, and ERK. In addition, A4 induced autophagy, as evidenced by increased expression of the autophagy biomarkers LC3B-II and Atg5, and autophagosomes formation. The antitumor activity of A4 also related to production of reactive oxygen species and adenosine monophosphate-activated protein kinase. Importantly, the an...

Scientific Reports, 2016

The antitumor activity of 3β,7β,25-trihydroxycucurbita-5,23(E)-dien-19-al (TCD), a triterpenoid i... more The antitumor activity of 3β,7β,25-trihydroxycucurbita-5,23(E)-dien-19-al (TCD), a triterpenoid isolated from wild bitter gourd, in breast cancer cells was investigated. TCD suppressed the proliferation of MCF-7 and MDA-MB-231 breast cancer cells with IC 50 values at 72 h of 19 and 23 μM, respectively, via a PPARγ−independent manner. TCD induced cell apoptosis accompanied with pleiotrophic biological modulations including down-regulation of Akt-NF-κB signaling, up-regulation of p38 mitogenactivated protein kinase and p53, increased reactive oxygen species generation, inhibition of histone deacetylases protein expression, and cytoprotective autophagy. Together, these findings provided the translational value of TCD and wild bitter gourd as an antitumor agent for patients with breast cancer.

Cancer Research, 2014

Activating KRAS mutations are the most frequent genetic abnormality in over 90% of pancreatic can... more Activating KRAS mutations are the most frequent genetic abnormality in over 90% of pancreatic cancers. Evidence indicates that these mutations not only play a crucial role in initiating pancreas carcinogenesis, but also are required for pancreatic tumor maintenance. From a clinical perspective, oncogenic KRAS represents a therapeutically relevant target in pancreatic cancer, of which the proof-of-concept was demonstrated by the effectiveness of siRNA-mediated silencing of KRAS to suppress pancreatic tumor growth in vivo. In this study, we have identified a novel KRAS-E2F1-ILK-hnRNP A1 regulatory circuitry that governs the expression of oncogenic KRAS. Integrin-linked kinase (ILK) is a serine/threonine kinase that mediates a diversity of cellular functions including cell survival, cell-matrix interactions, angiogenesis and also plays a role in epithelial to mesenchymal transition (EMT) in cancer cells. Dysregulation of ILK expression has been observed in several tumors including breast, ovary, melanoma, lung, prostate and pancreas and reported to be correlated with tumor progression, metastasis and chemoresistance to gemcitabine in pancreatic adenocarcinoma cells, but the mechanisms by which ILK is required for the tumorogenesis in pancreatic cancer are yet to be understood. In our study, oncogenic KRAS induces ILK expression via an E2F1-dependent mechanism, which, in turn, stimulates KRAS expression through hnRNP A1 upregulation. Mechanistically, hnRNP A1 binds and relaxes the Gquadruplex structure at the KRAS promoter, thereby enhancing the transcription initiation of the KRAS gene. As a result, disruption of this circuitry via siRNAmediated knockdown of any of these intermediary effectors (E2F1, ILK, or hnRNP A1), or pharmacological inhibition of ILK by T315, a novel ILK inhibitor developed in our laboratory, led to suppression of KRAS expression and reversal of the mesenchymal phenotype of pancreatic cancer cells. The therapeutic relevance of ILK in regulating this regulatory circuitry is also evident in the suppressive effect of ILK knockdown on epidermal growth factor (EGF)-induced KRAS expression. Together, these findings provide a rationale for targeting ILK as a novel strategy to suppress oncogenic KRAS signaling.

Journal of Biological Chemistry, 2012

Background: HuR regulates expression of many oncogenic proteins by modulating mRNA stability. Res... more Background: HuR regulates expression of many oncogenic proteins by modulating mRNA stability. Results: Glycolysis inhibition facilitates HuR degradation through a novel ␤-TrCP-mediated mechanism. Conclusion: This mechanism underlies the complexity in the regulation of HuR turnover under different stress stimuli. Significance: The ability of glycolysis inhibitors to target expression of oncogenic proteins by promoting HuR degradation might foster novel strategies for cancer therapy.

Carcinogenesis, 2009

Human p29 is a chromatin-associated protein and the silencing of p29 expression increases cell po... more Human p29 is a chromatin-associated protein and the silencing of p29 expression increases cell population in G 1 phase and decreases phosphorylation levels of Chk1 and Chk2 in response to UV treatment. To further characterize the function of p29, U2OS and Fanconi anemia complementation group G (FA-G) cells with constitutive p29 expression have been established. Analyses of these cells identified increased phosphorylation levels of Chk1 and Chk2, which were accompanied by elevated amounts of chromatinassociated Mre11-Rad50-Nbs1 complex and ATR-IP. Monoubiquitination of the FA ID complex was restored in p29 stably expressing FAG cells. Moreover, lower tumor incidence was observed in mp29 transgenic mice after UV irradiation. These results suggest the involvement of p29 in the DNA damage responses and Fanconi anemia pathway.

Cancer Research, 2011

Human hPuf-A/KIAA0020 was first identified as a new minor histocompatibility antigen in 2001. Its... more Human hPuf-A/KIAA0020 was first identified as a new minor histocompatibility antigen in 2001. Its zebrafish orthologue contains six Pumilio-homology RNA-binding domains and has been shown to participate in the development of eyes and primordial germ cells, but the cellular function of hPuf-A remains unclear. In this report, we showed that hPuf-A predominantly localized in the nucleoli with minor punctate signals in the nucleoplasm. The nucleolar localization of hPuf-A would redistribute to the nucleoplasm after the treatment of RNA polymerase inhibitors (actinomycin D and 5,6-dichlorobenzimidazole riboside) and topoisomerase inhibitors [camptothecin (CPT) and etoposide]. Interestingly, knockdown of hPuf-A sensitized cells to CPT and UV treatment and cells constitutively overexpressing hPuf-A became more resistant to genotoxic exposure. Affinity gel pull-down coupled with mass spectrometric analysis identified PARP-1 as one of the hPuf-A interacting proteins. hPuf-A specifically interacts with the catalytic domain of PARP-1 and inhibits poly(ADPribosyl)ation of PARP-1 in vitro. Depletion of hPuf-A increased the cleaved PARP-1 and overexpression of hPuf-A lessened PARP-1 cleavage when cells were exposed to CPT and UV light. Collectively, hPuf-A may regulate cellular response to genotoxic stress by inhibiting PARP-1 activity and thus preventing PARP-1 degradation by caspase-3. Cancer Res; 71(3); 1126-34. Ó2011 AACR.

Cancer Prevention Research, 2013

Cells undergoing malignant transformation often exhibit a shift in cellular metabolism from oxida... more Cells undergoing malignant transformation often exhibit a shift in cellular metabolism from oxidative phosphorylation to glycolysis. This glycolytic shift, called the Warburg effect, provides a mechanistic basis for targeting glycolysis to suppress carcinogenesis through the use of dietary caloric restriction and energy restriction-mimetic agents (ERMA). We recently reported the development of a novel class of ERMAs that exhibits high potency in eliciting starvation-associated cellular responses and epigenetic changes in cancer cells though glucose uptake inhibition. The lead ERMA in this class, OSU-CG5, decreases the production of ATP and NADH in LNCaP prostate cancer cells. In this study, we examined the effect of OSU-CG5 on the severity of preneoplastic lesions in male transgenic adenocarcinoma of the mouse prostate (TRAMP) mice. Daily oral treatment with OSU-CG5 at 100 mg/kg from 6 to 10 weeks of age resulted in a statistically significant decrease in the weight of urogenital tract and microdissected dorsal, lateral, and anterior prostatic lobes relative to vehicle controls. The suppressive effect of OSU-CG5 was evidenced by marked decreases in Ki67 immunostaining and proliferating cell nuclear antigen (PCNA) expression in the prostate. OSU-CG5 treatment was not associated with evidence of systemic toxicity. Microarray analysis indicated a central role for Akt, and Western blot analysis showed reduced phosphorylation and/or expression levels of Akt, Src, androgen receptor, and insulin-like growth factor-1 receptor in prostate lobes. These findings support further investigation of OSU-CG5 as a potential chemopreventive agent. Cancer Prev Res; 6(3); 232-41. Ó2012 AACR.

Biochemical and Biophysical Research Communications, 2004

Early detection and identification of SARS-CoV-infected patients and actions to prevent transmiss... more Early detection and identification of SARS-CoV-infected patients and actions to prevent transmission are absolutely critical to prevent another SARS outbreak. Antibodies that specifically recognize the SARS-CoV spike and nucleocapsid proteins may provide a rapid screening method to allow accurate identification and isolation of patients with the virus early in their infection. For this reason, we raised peptide-induced polyclonal antibodies against SARS-CoV spike protein and polyclonal antibodies against SARS-CoV nucleocapsid protein using 6Â His nucleocapsid recombinant protein. Western blot analysis and immunofluorescent staining showed that these antibodies specifically recognized SARS-CoV.

Cancer research, 2006

During the eukaryotic cell cycle, events in the G 1 and S phases are exquisitely controlled by a ... more During the eukaryotic cell cycle, events in the G 1 and S phases are exquisitely controlled by a multitude of regulators to ensure high fidelity during each round of DNA replication. These regulators include complexes of cyclin-dependent kinases (Cdk4/6) and cyclin D ( 1 3). ...

Substantial evidence supports the oncogenic role of the E3 ubiquitin ligase S-phase kinase-associ... more Substantial evidence supports the oncogenic role of the E3 ubiquitin ligase S-phase kinase-associated protein 2 (Skp2) in many types of cancers through its ability to target a broad range of signaling effectors for ubiquitination. Thus, this oncogenic E3 ligase represents an important target for cancer drug discovery. In this study, we report a novel mechanism by which CG-12, a novel energy restriction-mimetic agent (ERMA), down-regulates the expression of Skp2 in prostate cancer cells. Pursuant to our previous finding that upregulation of b-transducin repeat-containing protein (b-TrCP) expression represents a cellular response in cancer cells to ERMAs, including CG-12 and 2-deoxyglucose, we demonstrated that this b-TrCP accumulation resulted from decreased Skp2 expression. Evidence indicates that Skp2 targets b-TrCP for degradation via the cyclin-dependent kinase 2-facilitated recognition of the proline-directed phosphorylation motif 412 SP. This Skp2 downregulation was attributable to Sirt1-dependent suppression of COP9 signalosome (Csn)5 expression in response to CG-12, leading to increased cullin 1 neddylation in the Skp1-cullin1-F-box protein complex and consequent Skp2 destabilization. Moreover, we determined that Skp2 and b-TrCP are mutually regulated, providing a feedback mechanism that amplifies the suppressive effect of ERMAs on Skp2. Specifically, cellular accumulation of b-TrCP reduced the expression of Sp1, a b-TrCP substrate, which, in turn, reduced Skp2 gene expression. This Skp2-b-TrCP-Sp1 feedback loop represents a novel crosstalk mechanism between these two important F-box proteins in cancer cells with aberrant Skp2 expression under energy restriction, which provides a proof-of-concept that the oncogenic Csn5/Skp2 signaling axis represents a ''druggable'' target for this novel ERMA.