Histone lysine demethylase KDM4B regulates the alternative splicing of the androgen receptor in response to androgen deprivation.

Alternative splicing is emerging as an oncogenic mechanism. In prostate cancer, generation of constitutively active forms of androgen receptor (AR) variants including AR-V7 plays an important role in progression of castration-resistant prostate cancer (CRPC). AR-V7 is generated by alternative splicing that results in inclusion of cryptic exon CE3 and translation of truncated AR protein that lacks the ligand binding domain. Whether AR-V7 can be a driver for CRPC remains controversial as the oncogenic mechanism of AR-V7 activation remains elusive. Here, we found that KDM4B promotes AR-V7 and identified a novel regulatory mechanism. KDM4B is phosphorylated by protein kinase A under conditions that promote castration-resistance, eliciting its binding to the splicing factor SF3B3. KDM4B binds RNA specifically near the 5'-CE3, upregulates the chromatin accessibility, and couples the spliceosome to the chromatin. Our data suggest that KDM4B can function as a signal responsive trans-acting splicing factor and scaffold that recruits and stabilizes the spliceosome near the alternative exon, thus promoting its inclusion. Genome-wide profiling of KDM4B-regulated genes also identified additional alternative splicing events implicated in tumorigenesis. Our study defines KDM4B-regulated alternative splicing as a pivotal mechanism for generating AR-V7 and a contributing factor for CRPC, providing insight for mechanistic targeting of CRPC.

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.

Role of DAB2IP in modulating epithelial-to-mesenchymal transition and prostate cancer metastasis.

A single nucleotide polymorphism in the DAB2IP gene is associated with risk of aggressive prostate cancer (PCa), and loss of DAB2IP expression is frequently detected in metastatic PCa. However, the functional role of DAB2IP in PCa remains unknown. Here, we show that the loss of DAB2IP expression initiates epithelial-to-mesenchymal transition (EMT), which is visualized by repression of E-cadherin and up-regulation of vimentin in both human normal prostate epithelial and prostate carcinoma cells as well as in clinical prostate-cancer specimens. Conversely, restoring DAB2IP in metastatic PCa cells reversed EMT. In DAB2IP knockout mice, prostate epithelial cells exhibited elevated mesenchymal markers, which is characteristic of EMT. Using a human prostate xenograft-mouse model, we observed that knocking down endogenous DAB2IP in human carcinoma cells led to the development of multiple lymph node and distant organ metastases. Moreover, we showed that DAB2IP functions as a scaffold protein in regulating EMT by modulating nuclear beta-catenin/T-cell factor activity. These results show the mechanism of DAB2IP in EMT and suggest that assessment of DAB2IP may provide a prognostic biomarker and potential therapeutic target for PCa metastasis.

Therapeutic targeting of histone lysine demethylase KDM4B blocks the growth of castration-resistant prostate cancer.

Epigenetics is an emerging mechanism for tumorigenesis. Treatment that targets epigenetic regulators is becoming an attractive strategy for cancer therapy. The role of epigenetic therapy in prostate cancer (PCa) remains elusive. Previously we demonstrated that upregulation of histone lysine demethylase KDM4B correlated with the appearance of castration resistant prostate cancer (CRPC) and identified a small molecular inhibitor of KDM4B, B3. In this study, we further investigated the role of KDM4B in promoting PCa progression and tested the efficacy of B3 using clinically relevant PCa models including PCa cell line LNCaP and 22Rv1 and xenografts derived from these cell lines. In loss and gain-functional studies of KDM4B in PCa cells, we found that overexpression of KDM4B in LNCaP cells enhanced its tumorigenicity whereas knockdown of KDM4B in 22Rv1 cells reduced tumor growth in castrated mice. B3 suppressed the growth of 22Rv1 xenografts and sensitized tumor to anti-androgen receptor (AR) antagonist enzalutamide inhibition. B3 also inhibited 22Rv1 tumor growth synergistically with rapamycin, leading to cell apoptosis. Comparative transcriptomic analysis performed on KDM4B knockdown and B3-treated 22Rv1 cells revealed that B3 inhibited both H3K9me3 and H3K27me3 demethylase activities. Our studies establish KDM4B as a target for CRPC and B3 as a potential therapeutic agent. B3 as monotherapy or in combination with other anti-PCa therapeutics offers proof of principle for the clinical translation of epigenetic therapy targeting KDMs for CRPC patients.

Analysis of oligo-arginine cell-permeable peptides uptake by prostate cells.

Recently, we have shown that oligo-arginine peptide (i.e., R11), a unique cell-permeable peptide (CPP), can be used as an imaging probe for prostate cancer detection. In this study, the mechanism(s) of oligo-arginine peptide in prostate cells was further analyzed. The length of the oligo-arginine peptide appears to be critical for the efficiency of uptake by prostate cells: poly (11)-arginine (R11) > poly (9)-arginine (R9) > poly (13)-arginine peptide (R13). The uptake of R11 peptide by prostate cells is mediated by macropinocytosis as evidenced by the fact that uptake can be blocked by a macropinocytosis inhibitor. However, the use of an inhibitor for carbohydrate chain elongation of glycosaminoglycan or inhibitors for carbohydrate synthesis of glycoprotein via either O-link or N-link showed minimal effects on R11 uptake. Nevertheless, pentosan sulfate (PentS) or dextran sulfate (DS) exhibited the highest inhibitory effect on R11 uptake in several prostate cells treated with various soluble glycosaminoglycans (GAGs) or anionic polymers. It is known that laminin receptor has been characterized as a PentS binding partner. Knocking down 37LRP (laminin receptor precursor) expression in prostate cells showed a reduction in their ability to uptake R11 peptides. In conclusion, laminin receptor is one of the initial binding site(s) responsible for R11 peptide uptake in prostate cells.

DAB2IP coordinates both PI3K-Akt and ASK1 pathways for cell survival and apoptosis.

In metastatic prostate cancer (PCa) cells, imbalance between cell survival and death signals such as constitutive activation of phosphatidylinositol 3-kinase (PI3K)-Akt and inactivation of apoptosis-stimulated kinase (ASK1)-JNK pathways is often detected. Here, we show that DAB2IP protein, often down-regulated in PCa, is a potent growth inhibitor by inducing G(0)/G(1) cell cycle arrest and is proapoptotic in response to stress. Gain of function study showed that DAB2IP can suppress the PI3K-Akt pathway and enhance ASK1 activation leading to cell apoptosis, whereas loss of DAB2IP expression resulted in PI3K-Akt activation and ASK1-JNK inactivation leading to accelerated PCa growth in vivo. Moreover, glandular epithelia from DAB2IP(-/-) animal exhibited hyperplasia and apoptotic defect. Structural functional analyses of DAB2IP protein indicate that both proline-rich (PR) and PERIOD-like (PER) domains, in addition to the critical role of C2 domain in ASK1 activity, are important for modulating PI3K-Akt activity. Thus, DAB2IP is a scaffold protein capable of bridging both survival and death signal molecules, which implies its role in maintaining cell homeostasis.

The central role of Sphingosine kinase 1 in the development of neuroendocrine prostate cancer (NEPC): A new targeted therapy of NEPC.

BACKGROUND: Neuroendocrine prostate cancer (NEPC) is often diagnosed as a sub-type from the castration-resistant prostate cancer (CRPC) recurred from the second generation of anti-androgen treatment and is a rapidly progressive fatal disease. The molecular mechanisms underlying the trans-differentiation from CRPC to NEPC are not fully characterized, which hampers the development of effective targeted therapy. METHODS: Bioinformatic analyses were conducted to determine the clinical correlation of sphingosine kinase 1 (SphK1) in CRPC progression. To investigate the transcriptional regulation SphK1 and neuroendocrine (NE) transcription factor genes, both chromosome immunoprecipitation and luciferase reporter gene assays were performed. To demonstrate the role of SphK1 in NEPC development, neurosphere assay was carried out along with several biomarkers determined by quantitative PCR and western blot. Furthermore, in vivo NEPC xenograft models and patient-derived xenograft (PDX) model were employed to determine the effect of SphK1 inhibitors and target validation. RESULTS: Significant prevalence of SphK1 in NEPC development is observed from clinical datasets. SphK1 is transcriptionally repressed by androgen receptor-RE1-silencing transcription factor (REST) complex. Furthermore, sphingosine 1-phosphate produced by SphK1 can modulate REST protein turnover via MAPK signaling pathway. Also, decreased REST protein levels enhance the expression of NE markers in CRPC, enabling the transition to NEPC. Finally, specific SphK1 inhibitors can effectively inhibit the growth of NEPC tumors and block the REST protein degradation in PDX. CONCLUSIONS: SphK1 plays a central role in NEPC development, which offers a new target for this lethal cancer using clinically approved SphK1 inhibitors.

Upregulation of TRAG3 gene in urothelial carcinoma of the bladder.

Conventional chemotherapy is commonly used for advanced stages of bladder cancer with modest success and high morbidity. Identifying markers of resistance will allow clinicians to tailor treatment to a specific patient population. T24-tumorigenic cell line was grown orthotopically in nude mice and monitored using bioluminescence imaging and microcomputed tomography until they developed metastases. Stable sublines were then developed from primary bladder (T24-P), lung (T24-L) and bone (T24-B) tissues. Chromosomal analysis and DNA microarray were used to characterize these sublines. Real-time quantitative polymerase chain reaction and immunohistochemistry were used for validation. Epigenetic modifiers were used to study gene regulation. The cell viability was quantified with MTT assay. Chromosomal analysis revealed multiple alterations in metastatic cell lines compared to T24-P. DNA microarray analysis showed that taxol resistance-associated gene (TRAG) 3 was the most upregulated gene. From real-time quantitative polymerase chain reaction and immunohistochemistry, TRAG3 was significantly higher in T24-L and T24-B than T24-P. TRAG3 gene expression is likely controlled by DNA methylation but not histone acetylation. Interestingly, T24-B and T24-L cells were more resistant than T24-P to treatment with antimicrotubule agents such as docetaxel, paclitaxel and vinblastine. TRAG3 mRNA expression was higher in 20% of patients with ≤ pT2 (n = 10) and 60% of patients with ≥ pT3 (n = 20) compared to normal adjacent tissue (p = 0.05). In addition, the median TRAG3 expression was 6.7-fold higher in ≥ pT3 tumors compared to ≤ pT2 tumors. Knowing the status of TRAG3 expression could help clinicians tailor treatment to a particular patient population that could benefit from treatment, while allocating patients with resistant tumors to new experimental therapies.

Evidence of epithelial to mesenchymal transition associated with increased tumorigenic potential in an immortalized normal prostate epithelial cell line.

BACKGROUND: The majority of established human prostate cancer cell lines are derived from metastatic lesions and are already tumorigenic in vivo, therefore immortalized normal prostate cell lines may provide a more relevant model to unveil the mechanisms associated with cancer progression and metastasis. METHODS: PZ-HPV-7, an immortalized human prostate epithelial cell line was used to generate xenograft tumors in mice. A subline designated HPV-PZ-7T was subsequently derived from the subrenal capsule xenograft of a nude mouse. These cells were further characterized using karyotyping, immunofluorescence, qRT-PCR, Western blotting, and three-dimensional cultures in Matrigel. RESULTS: The PZ-HPV-7 cell line possesses a typical epithelial morphology, expresses basal cell markers, and is capable of forming web-like structures with evidence of budding on Matrigel. PZ-HPV-7 is non-tumorigenic in immunocompromised mice by either subcutaneous injection or subrenal grafting. In contrast, the PZ-HPV-7T cells, derived from a xenograft tumor induced by co-inoculation with matrigel using subrenal grafting, possess a mesenchymal phenotype as well as luminal cell markers and are highly tumorigenic and metastatic in nude mice. Functionally and biochemically, the PZ-HPV-7T subline appears to have undergone an epithelial-to-mesenchymal transition (EMT) from the parental PZ-HPV-7 line. CONCLUSION: We have developed a novel EMT model using an immortalized normal prostate epithelial cell line and generated a new prostate cancer cell line, PZ-HPV-7T, which may represent an excellent system to study mechanisms associated with prostate cancer progression and metastasis.

The roles and mechanism of IFIT5 in bladder cancer epithelial-mesenchymal transition and progression.

The prognosis of bladder cancer (BCa) depends on several key factors including anatomical site, tumor grade, and stage. In general, muscle-invasive bladder cancer (MIBC) is associated with higher incidence of distant metastasis compared with Non-muscle-invasive bladder cancer (NMIBC). Treatment outcome of the patients with metastatic BCa has been very poor with ~15% of overall survival rate. Thus, it is apparently important to understand the underlying biology for metastatic progression of BCa. Although epithelial-mesenchymal transition (EMT) has long been implicated in BCa metastasis and treatment resistance, the underlying mechanism is not fully understood. In this study, we have identified that the expression of interferon induced protein with tetratricopeptide repeats 5 (IFIT5) is positively correlated with pathological characteristics, and predicts a poor prognosis of BCa patients. Since the function of IFIT5 in BCa has not yet been characterized, we demonstrate that IFIT5 can induce EMT, promote cell migration and invasion, and increase the expression of ICAM1 in BCa via down-regulation of mature miR-99a. Moreover, ICAM1 is shown as a direct target of miR-99a. Overall, we conclude that IFIT5 is a new oncogene in BCa.

Activation of sphingosine kinase by lipopolysaccharide promotes prostate cancer cell invasion and metastasis via SphK1/S1PR4/matriptase.

Gram-negative bacteria have been found to be a major population in prostatitis and prostate cancer (PCa) tissues. Lipopolysaccharide (LPS), a major compound of Gram-negative bacteria, with stimulatory activities in some cancer types, but has not been fully studied in PCa. In this study, we examined the effect of LPS on the invasion of PCa cells. Interestingly, LPS can enhance the invasiveness of PCa, but had no significant effect on PCa cell viability. Using protease inhibitor screening and biochemical analyses, matriptase, a member of the membrane-anchored serine protease family, is found to play a key role in LPS-induced PCa cell invasion. Mechanistically, Toll-like receptor 4 (TLR4, LPS receptor)-sphingosine kinase 1 (SphK1) signaling underlies LPS-induced matriptase activation and PCa cell invasion. Specifically, LPS induced the S225 phosphorylation of SphK1 and the translocation of SphK1 to plasma membrane, leading to the production of sphingosine 1-phosphate (S1P), ERK1/2 and matriptase activation via S1P receptor 4 (S1PR4). This phenomenon is further validated using the patient-derived explant (PDE) model. Indeed, there is a significant correlation among the elevated SphK1 levels, the Gleason grades of PCa specimens, and the poor survival of PCa patients. Taken together, this study demonstrates a potential impact of LPS on PCa progression. Our results provide not only a new finding of the role of bacterial infection in PCa progression but also potential therapeutic target(s) associated with PCa metastasis.

IFNγ-Induced IFIT5 Promotes Epithelial-to-Mesenchymal Transition in Prostate Cancer via miRNA Processing.

IFNγ, a potent cytokine known to modulate tumor immunity and tumoricidal effects, is highly elevated in patients with prostate cancer after radiation. In this study, we demonstrate that IFNγ can induce epithelial-to-mesenchymal transition (EMT) in prostate cancer cells via the JAK-STAT signaling pathway, leading to the transcription of IFN-stimulated genes (ISG) such as IFN-induced tetratricopeptide repeat 5 (IFIT5). We unveil a new function of IFIT5 complex in degrading precursor miRNAs (pre-miRNA) that includes pre-miR-363 from the miR-106a-363 cluster as well as pre-miR-101 and pre-miR-128, who share a similar 5'-end structure with pre-miR-363. These suppressive miRNAs exerted a similar function by targeting EMT transcription factors in prostate cancer cells. Depletion of IFIT5 decreased IFNγ-induced cell invasiveness in vitro and lung metastasis in vivo. IFIT5 was highly elevated in high-grade prostate cancer and its expression inversely correlated with these suppressive miRNAs. Altogether, this study unveils a prometastatic role of the IFNγ pathway via a new mechanism of action, which raises concerns about its clinical application.Significance: A unique IFIT5-XRN1 complex involved in the turnover of specific tumor suppressive microRNAs is the underlying mechanism of IFNγ-induced epithelial-to-mesenchymal transition in prostate cancer.See related commentary by Liu and Gao, p. 1032.

Decreased DOC-2/DAB2 expression in urothelial carcinoma of the bladder.

PURPOSE: DOC-2/DAB2 (differentially expressed in ovarian carcinoma-2/disabled-2), a potential tumor suppressor gene, is underexpressed in several cancers. Little is known about the expression of this gene in urothelial carcinoma of the bladder (UCB). We profiled DOC-2/DAB2 expression in mouse and human normal and neoplastic urothelia. EXPERIMENTAL DESIGN: Immunohistochemical staining for DOC-2/DAB2 was carried out on tissue specimens from two transgenic mouse models with urothelium-specific molecular alterations and on a tissue microarray containing cores from 9 normal controls, 44 patients who underwent transurethral resection of the bladder tumor (TURBT), 195 patients who underwent radical cystectomy for UCB, and 39 lymph nodes with metastatic UCB. RESULTS: Normal mouse urothelium stained uniformly with DOC-2/DAB2. Weaker staining was observed in low-grade, superficial papillary bladder tumors from transgenic mice harboring constitutively active Ha-Ras, whereas carcinoma in situ-like lesions and high-grade bladder tumors from transgenic mice expressing a SV40 T antigen completely lacked DOC-2/DAB2 expression. In human tissues, DOC-2/DAB2 expression was decreased in 11% of normal bladder specimens, 59% of TURBT specimens, 65% of radical cystectomy specimens, and 77% of the metastatic lymph node specimens. Decreased DOC-2/DAB2 expression was associated with advanced pathologic stage (P = 0.023), lymph node metastases (P = 0.050), and lymphovascular invasion (P < 0.001). In univariable, but not in multivariable analysis, decreased DOC-2/DAB2 was associated with an increased probability of bladder cancer recurrence (log-rank test, P = 0.020) and bladder cancer-specific mortality (log-rank test, P = 0.023). CONCLUSIONS: Decreased DOC-2/DAB2 expression seems to occur early in bladder tumorigenesis and becomes more prominent in advanced stages of UCB.

Targeting 3-phosphoinositide-dependent protein kinase 1 associated with drug-resistant renal cell carcinoma using new oridonin analogs.

The current agents used for renal cell carcinoma (RCC) only exhibit the moderate response rate among patients. Development of drug resistance eventually fuels the need of either more potent drugs or new drugs to target the resistant pathways. Oridonin is a diterpenoid isolated from the Chinese medicinal herb Rabdosia rubescens and has been shown to have antitumor activities in many cancers. We previously developed new synthetic methodologies to modify structurally diversified diterpenoids and designed a series of nitrogen-enriched oridonin analogs. In this study, we screened a variety of oridonin analogs based on their cytotoxicity using MTT assay and identify the most potent candidate, namely, CYD-6-17. CYD-6-17 exhibited a high potency to inhibit the in vitro growth of several drug-resistant RCC cells as well as endothelial cells stimulated by tumor cells at nanomolar range. Delivery of CYD-6-17 significantly inhibited RCC tumor growth using xenograft model. Mechanistically, it targeted the 3-phosphoinositide-dependent protein kinase 1 gene that appeared to be a potent regulator of AKT and was associated with patient survival after targeted therapies. This offers a new rational therapeutic regimen of CYD-6-17 to drug-resistant RCC based on its novel mechanism of action.

Epigenetic regulation of coxsackie and adenovirus receptor (CAR) gene promoter in urogenital cancer cells.

Coxsackie and adenovirus receptor (CAR) is not only a high-affinity receptor for adenovirus, but also a tumor inhibitor in both prostate and bladder cancer lines. Decreased CAR gene expression is often detected in cancer specimens; however, the mechanism(s) is still unknown. In this study, we cloned the entire CAR gene and characterized the core promoter sequence of the CAR gene. The CAR gene promoter activity correlated with the differential expression of CAR mRNA levels from several urogenital cancer cell lines, indicating that the down-regulation of CAR gene expression is mediated by transcriptional regulation. It is known that epigenetic control, such as DNA methylation and histone acetylation of chromatin structure, dictates gene expression. Data from this study indicate that the activation of the CAR gene promoter is modulated by histone acetylation, but not by DNA methylation, in urogenital cancer cells. Also, a potent cancer chemotherapeutic agent (FR901228), a histone deacetylase inhibitor, was able to induce endogenous CAR gene expression in several urogenital cancer cells. Taken together, epigenetic control of CAR gene underlies the down-regulation of this gene in urogenital cancers.

Nanoparticle Targeting CD44-Positive Cancer Cells for Site-Specific Drug Delivery in Prostate Cancer Therapy.

Prostate cancer is one of the leading causes of cancer death in adult men and is a multistage disease with therapeutic challenges of local recurrent advanced tumors and distant metastatic disease. CD44 is a multifunctional and multistructural cell surface glycoprotein that is involved in cell-cell interactions, cell proliferation, and cell migration. In the study, we produced negatively charged and biocompatible hyaluronic acid-based nanoparticles as a therapeutic system for targeting CD44-positive cancer cells. Subsequently, we confirmed the delivery of bioactive epigallocatechin-3-gallate and site-specific inhibition of prostate tumor growth. In this study, hyaluronic acid-based nanoparticles successfully encapsulated epigallocatechin-3-gallate and were efficiently internalized into cancer cells via CD44 ligand receptor recognition, induced cell cycle arrest at G2/M phase, and inhibited prostate cancer cell growth. Furthermore, in vivo assays indicated that these nanoparticles specifically bind CD44 receptors and increase apoptosis of cancer cells, leading to significant decreases in prostate tumor activity and tumor tissue inflammation.

Surrogate marker for predicting the virus binding of urogenital cancer cells during adenovirus-based gene therapy.

Virus uptake is the first rate-limiting step for the successful gene delivery of any virus-based gene therapy. For adenovirus-based gene therapy, the expression levels of the adenovirus receptor--coxsackievirus and adenovirus receptor (CAR)--play an important role in dictating gene delivery. We have observed a wide spectrum of CAR expression among cancer cell lines and tumor specimens. Therefore, the screening of the CAR expression level in patients becomes crucial for any possible positive outcome. In this paper, we establish a real-time RT-PCR assay for the detection of CAR mRNA levels from cancer cells and tumor specimens. This assay appears to be very quantitative, with sample concentrations ranging within 6 logs, and the sensitivity of this assay could detect as low as 1.8 x 10(2) copies of CAR cDNA per reaction. The results from this assay confirmed that there was a good linear relationship between the CAR mRNA and virus binding from each cell line. With this assay, we were able to detect changes in CAR gene expression in cells treated with histone deacetylase inhibitor. Most importantly, CAR mRNA levels directly correlated with its protein levels prepared from tumor specimens. Taken together, this assay could provide a rapid screening tool for any adenovirus-based gene therapy trial.

The role of cell adhesion molecule in cancer progression and its application in cancer therapy.

Multiple and diverse cell adhesion molecules take part in intercellular and cell-extracellular matrix interactions of cancer. Cancer progression is a multi-step process in which some adhesion molecules play a pivotal role in the development of recurrent, invasive, and distant metastasis. A growing body of evidence indicates that alterations in the adhesion properties of neoplastic cells play a pivotal role in the development and progression of cancer. Loss of intercellular adhesion and the desquamation of cells from the underlying lamina propria allows malignant cells to escape from their site of origin, degrade the extracellular matrix, acquire a more motile and invasion phenotype, and finally, invade and metastasize. In addition to participating in tumor invasiveness and metastasis, adhesion molecules regulate or significantly contribute to a variety of functions including signal transduction, cell growth, differentiation, site-specific gene expression, morphogenesis, immunologic function, cell motility, wound healing, and inflammation. Cell adhesion molecule (CAM), a diverse system of transmembrane glycoproteins has been identified that mediates the cell-cell and cell-extracellular matrix adhesion and also serves as the receptor for different kinds of virus. We summarize recent progress regarding the role of CAM, particularly, immunoglobulin-CAMs and cadherins in the progression of cancer and discuss the potential application of CAMs in the development of cancer therapy mainly on urogenital cancer.

Sensitization of radio-resistant prostate cancer cells with a unique cytolethal distending toxin.

Cytolethal distending toxin (CDT) produced by Campylobacter jejuni is a genotoxin that induces cell-cycle arrest and apoptosis in mammalian cells. Recent studies have demonstrated that prostate cancer (PCa) cells can acquire radio-resistance when DOC-2/DAB2 interactive protein (DAB2IP) is downregulated. In this study, we showed that CDT could induce cell death in DAB2IP-deficient PCa cells. A combination of CDT and radiotherapy significantly elicited cell death in DAB2IP-deficient PCa cells by inhibiting the repair of ionizing radiation (IR)-induced DNA double-strand break (DSB) during G2/M arrest, which is triggered by ataxia telangiectasia mutated (ATM)-dependent DNA damage checkpoint responses. We also found that CDT administration significantly increased the efficacy of radiotherapy in a xenograft mouse model. These results indicate that CDT can be a potent therapeutic agent for radio-resistant PCa.

The mechanism of DAB2IP in chemoresistance of prostate cancer cells.

PURPOSE: The docetaxel-based chemotherapy is the standard of care for castration-resistant prostate cancer (CRPC), inevitably, patients develop resistance and decease. Until now, the mechanism and predictive marker for chemoresistance are poorly understood. EXPERIMENTAL DESIGN: Immortalized normal prostate and cancer cell lines stably manipulated with different DAB2IP expression levels were used and treated with chemotherapeutic drugs commonly used in prostate cancer therapy. Cell proliferation was measured using MTT assay; Western blot, quantitative PCR, and luciferase reporter assays were used to analyze Clusterin gene regulation by DAB2IP. Immunohistochemical analysis was conducted for evaluating DAB2IP, Clusterin and Egr-1 expression in human prostate cancer tissue. RESULTS: DAB2IP Knockdown (KD) cells exhibited resistance to several chemotherapeutic drugs, whereas increased DAB2IP in C4-2 cells restored the drug sensitivity. Parallel, DAB2IP KD cells exhibited higher expression of Clusterin, an antiapoptotic factor, whereas elevated DAB2IP in C4-2 cells decreased Clusterin expression. Functionally, knocking down Clusterin by short-hairpin RNA or antisense oligonucleotide OGX-011 decreased drug resistance, whereas overexpressing Clusterin in C4-2 D2 enhanced drug resistance. Mechanistically, DAB2IP blocked the cross-talk between Wnt/ß-catenin and IGF-I signaling, leading to the suppression of Egr-1 that is responsible for Clusterin expression. A similar result was observed in the prostate of DAB2IP knockout animals. In addition, we observed a significantly inverse correlation between DAB2IP and Egr-1 or Clusterin expression from clinical tissue microarray. CONCLUSIONS: This study unveils a new regulation of the Egr-1/Clusterin signaling network by DAB2IP. Loss of DAB2IP expression in CRPC cells signifies their chemoresistance. Clusterin is a key target for developing more effective CRPC therapy.