Over-expression of survivin is a factor responsible for differential responses of ovarian cancer cells to S-allylmercaptocysteine (SAMC).

While investigating the inhibitory effect of S-allylmercaptocysteine (SAMC), a garlic derivative, on ovarian cancer, we subjected three ovarian cancer cell lines, HO8910, HO8910PM, and SKOV3, to SAMC treatment. In vivo and in vitro experiments showed that only HO8910 and SKOV3 cells were highly sensitive to SAMC, whereas HO8910PM cells were resistant to SAMC. Subsequently, we examined the apoptosis-related genes in the three cell lines. We found that survivin gene was highly expressed in HO8910PM cells. Down regulation of survivin gene in HO8910PM cells with small interference RNA (siRNA), resulted in increased sensitivity to SAMC together with a decrease in invasiveness of tumor cells. We therefore concluded that the S-allylmercaptocysteine suppresses both the proliferation and distant metastasis of epithelial ovarian cancer cells, insensitivity of HO8910PM cells to SAMC was closely related to the high level of survivin expression and that combination of SAMC treatment together with survivin knockdown might be a potential strategy for treatment of certain variants of ovarian cancers.

Inactivation of ATM/ATR DNA damage checkpoint promotes androgen induced chromosomal instability in prostate epithelial cells.

The ATM/ATR DNA damage checkpoint functions in the maintenance of genetic stability and some missense variants of the ATM gene have been shown to confer a moderate increased risk of prostate cancer. However, whether inactivation of this checkpoint contributes directly to prostate specific cancer predisposition is still unknown. Here, we show that exposure of non-malignant prostate epithelial cells (HPr-1AR) to androgen led to activation of the ATM/ATR DNA damage response and induction of cellular senescence. Notably, knockdown of the ATM gene expression in HPr-1AR cells can promote androgen-induced TMPRSS2: ERG rearrangement, a prostate-specific chromosome translocation frequently found in prostate cancer cells. Intriguingly, unlike the non-malignant prostate epithelial cells, the ATM/ATR DNA damage checkpoint appears to be defective in prostate cancer cells, since androgen treatment only induced a partial activation of the DNA damage response. This mechanism appears to preserve androgen induced autophosphorylation of ATM and phosphorylation of H2AX, lesion processing and repair pathway yet restrain ATM/CHK1/CHK2 and p53 signaling pathway. Our findings demonstrate that ATM/ATR inactivation is a crucial step in promoting androgen-induced genomic instability and prostate carcinogenesis.

Physalins A and B inhibit androgen-independent prostate cancer cell growth through activation of cell apoptosis and downregulation of androgen receptor expression.

Androgen deprivation therapy is a common treatment strategy for advanced prostate cancer. Though effective initially, the tumor often progresses to androgen independent stage in most patients eventually after a period of remission. One of the key factors of development of resistance is reflected in expression of androgen receptor (AR). In this study, we showed that two natural compounds, physalins A and B, both secosteriods from Physalisalkekengi var. franchetii, significantly inhibited the growth of two androgen-independent cell lines CWR22Rv1 and C42B, induced apoptosis via c-Jun N-terminal kinase (JNK) and/or extracellular signal-regulated kinase (ERK) activation, and decreased AR expression. In addition, physalins A and B down-regulated the expression of prostate specific antigen (PSA) in C42B cells which is a target gene of AR. Our results suggest that physalin A and B might be useful agents in preventing the growth of androgen-independent prostate cancer (AI-PCa).

S-allylmercaptocysteine effectively inhibits the proliferation of colorectal cancer cells under in vitro and in vivo conditions.

S-allylmercaptocysteine (SAMC), one of the water-soluble organosulfur garlic derivatives, has been demonstrated as a suppressive agent against some tumors. The effects of SAMC on the proliferation and metastasis of colorectal cancer (CRC) under in vitro and in vivo conditions were evaluated here. The viabilities and migrations of CRC cells SW480, SW620, Caco-2 treated with SAMC were measured by MTT, scratch-wound, and transwell assays. The in vivo anticancer effect of SAMC against luciferase-expressing SW620 xenografts in mice was determined by bioluminescence imaging and histopathology observation. The apoptosis of SAMC-treated CRC cells was examined by Western blotting. The results demonstrate that SAMC could effectively suppress the growth and metastasis of colorectal cancer cells both in vivo and in vitro. The anticancer effect of SAMC was related to the decreased proliferation and increased apoptosis as well as necrosis of cancer cells. Oral administration of SAMC in the quantity/concentration used had no apparent toxic side effect on the vital organs of the experimental mice. Taken together, the proliferation and metastasis of CRC cells can be significantly suppressed by SAMC treatment under both in vitro and in vivo conditions. SAMC may thus be a promising candidate for CRC chemotherapy.

Chemopreventive effect of PSP through targeting of prostate cancer stem cell-like population.

Recent evidence suggested that prostate cancer stem/progenitor cells (CSC) are responsible for cancer initiation as well as disease progression. Unfortunately, conventional therapies are only effective in targeting the more differentiated cancer cells and spare the CSCs. Here, we report that PSP, an active component extracted from the mushroom Turkey tail (also known as Coriolus versicolor), is effective in targeting prostate CSCs. We found that treatment of the prostate cancer cell line PC-3 with PSP led to the down-regulation of CSC markers (CD133 and CD44) in a time and dose-dependent manner. Meanwhile, PSP treatment not only suppressed the ability of PC-3 cells to form prostaspheres under non-adherent culture conditions, but also inhibited their tumorigenicity in vivo, further proving that PSP can suppress prostate CSC properties. To investigate if the anti-CSC effect of PSP may lead to prostate cancer chemoprevention, transgenic mice (TgMAP) that spontaneously develop prostate tumors were orally fed with PSP for 20 weeks. Whereas 100% of the mice that fed with water only developed prostate tumors at the end of experiment, no tumors could be found in any of the mice fed with PSP, suggesting that PSP treatment can completely inhibit prostate tumor formation. Our results not only demonstrated the intriguing anti-CSC effect of PSP, but also revealed, for the first time, the surprising chemopreventive property of oral PSP consumption against prostate cancer.

Gamma-tocotrienol as an effective agent in targeting prostate cancer stem cell-like population.

Emerging evidence supports that prostate cancer originates from a rare subpopulation of cells, namely prostate cancer stem cells (CSCs). Conventional therapies for prostate cancer are believed to mainly target the majority of differentiated tumor cells but spare CSCs, which may account for the subsequent disease relapse after treatment. Therefore, successful elimination of CSCs may be an effective strategy to achieve complete remission from this disease. Gamma-tocotrienols (γ-T3) is one of the vitamin-E constituents, which have been shown to have anticancer effects against a wide range of human cancers. Recently, we have reported that γ-T3 treatment not only inhibits prostate cancer cell invasion but also sensitizes the cells to docetaxel-induced apoptosis, suggesting that γ-T3 may be an effective therapeutic agent against advanced stage prostate cancer. Here, we demonstrate for the first time that γ-T3 can downregulate the expression of prostate CSC markers (CD133/CD44) in androgen-independent prostate cancer cell lines (PC-3 and DU145), as evident from Western blotting analysis. Meanwhile, the spheroid formation ability of the prostate cancer cells was significantly hampered by γ-T3 treatment. In addition, pretreatment of PC-3 cells with γ-T3 was found to suppress tumor initiation ability of the cells. More importantly, although CD133-enriched PC-3 cells were highly resistant to docetaxel treatment, these cells were as sensitive to γ-T3 treatment as the CD133-depleted population. Our data suggest that γ-T3 may be an effective agent in targeting prostate CSCs, which may account for its anticancer and chemosensitizing effects reported in previous studies.

Differential expression of MSX2 in nodular hyperplasia, high-grade prostatic intraepithelial neoplasia and prostate adenocarcinoma.

One of the common features in advanced prostate cancer is bone metastasis. In this study, we investigated the clinical relevance of a bone factor, MSX2, in predicting the metastatic ability of prostate adenocarcinoma. Evaluation of MSX2 expression was performed using prostate cell lines as well as patient specimens. A sharp decrease in MSX2 was found in primary prostate cancer cells, 22Rv1, when compared with the non-malignant counterparts, followed by a gradual increase in more aggressive prostate cancer cell lines. Interestingly, the MSX2 protein was upregulated and predominantly expressed in the nucleus in aggressive prostate cancer cell line, C4-2b, compared with the less aggressive 22Rv1. Consistent with the in vitro results, MSX2 nuclear expression was significantly higher in nodular hyperplasia when compared with high-grade prostatic intraepithelial neoplasia (PIN), while MSX2 nuclear expression in prostate adenocarcinoma was higher than that in high-grade PIN. Importantly, MSX2 expression was increased significantly in tumors with metastasis compared with those without metastasis. Finally, MSX2 nuclear scores were significantly increased in patients with preoperative serum PSA >20 ng/mL. No correlation between MSX2 nuclear score and Gleason score was found. Taken together, MSX2 may serve as a potential biomarker in predicting primary prostate tumors with higher metastatic capability.

Suppression of androgen-independent prostate cancer cell aggressiveness by FTY720: validating Runx2 as a potential antimetastatic drug screening platform.

PURPOSE: Previously, FTY720 was found to possess potent anticancer effects on various types of cancer. In the present study, we aimed to first verify the role of Runx2 in prostate cancer progression and metastasis, and, subsequently, assessed if FTY720 could modulate Runx2 expression, thus interfering downstream events regulated by this protein. EXPERIMENTAL DESIGN: First, the association between Runx2 and prostate cancer progression was assessed using localized prostate cancer specimens and mechanistic investigation of Runx2-induced cancer aggressiveness was then carried out. Subsequently, the effect of FTY720 on Runx2 expression and transcriptional activity was investigated using PC-3 cells, which highly expressed Runx2 protein. Last, the involvement of Runx2 in FTY720-induced anticancer effects was evaluated by modulating Runx2 expression in various prostate cancer cell lines. RESULTS: Runx2 nuclear expression was found to be up-regulated in prostate cancer and its expression could be used as a predictor of metastasis in prostate cancer. Further mechanistic studies indicated that Runx2 accelerated prostate cancer aggressiveness through promotion of cadherin switching, invasion toward collagen I, and Akt activation. Subsequently, we found that FTY720 treatment down-regulated Runx2 expression and its transcriptional activity, as well as inhibited its regulated downstream events. More importantly, silencing Runx2 in PC-3 enhanced FTY720-induced anticancer effects as well as cell viability inhibition, whereas overexpressing Runx2 in 22Rv1 that expressed very low endogenous Runx2 protein conferred resistance in the same events. CONCLUSION: This study provided a novel mechanism for the anticancer effect of FTY720 on advanced prostate cancer, thus highlighting the therapeutic potential of this drug in treating this disease.

CDC25A functions as a novel Ar corepressor in prostate cancer cells.

Androgen receptor (AR) is a ligand-dependent transcription factor and its activity is regulated by numerous AR coregulators. Aberrant expression of AR coregulators in prostate cancer cells has an important role in the development and progression of prostate cancer. We report here that CDC25A, a cell cycle-promoting phosphatase over-expressed in a number of cancers, functions as an AR coregulator suppressing the AR transcriptional activity. In this study, we found that CDC25A is upregulated in human prostate cancer and its expression level is positively associated with the Gleason score and disease metastasis. More importantly, we showed that CDC25A can physically interact with AR through its putative catalytic domain. In addition, ectopic expression of CDC25A in prostate cancer cell lines suppresses PSA and Probasin promoter activities significantly, indicating that CDC25A may function as an AR corepressor. This was further confirmed by knockdown of endogenous CDC25A expression using small interfering RNA (siRNA), which resulted in upregulation of PSA promoter activity. Moreover, a truncated mutant that does not interact with AR fails to suppress the PSA promoter activity, indicating that CDC25A downregulates androgen-responsive promoter by physically interacting with AR. Taken together, our results demonstrated a novel function of CDC25A in the regulation of androgen signaling in human prostate cancer cells.

The prognostic significance of BMP-6 signaling in prostate cancer.

The importance of bone-morphogenetic proteins in prostate cancer is well recognized. Bone-morphogenetic protein-6 overexpression has been shown to increase the aggressiveness and invasiveness of prostate cancer cells. Recent studies on noggin and sclerostin, potent inhibitors of bone-morphogenetic protein signaling, have found that noggin also modifies the ability of prostate cancer cells to metastasize to bone. Taken together, these results suggest that bone-morphogenetic protein-6 signaling is important in prostate cancer progression. Our study investigated the expression of bone-morphogenetic protein-6, noggin and sclerostin in human prostate specimens (n=136) by immunohistochemical staining. We found that bone-morphogenetic protein-6 was increased (P<0.001), whereas sclerostin was decreased (P=0.004) in prostate cancer compared with nodular hyperplasia. In addition, significantly higher level of bone-morphogenetic protein-6 expression was observed in high-grade prostate cancer with Gleason score >or=7 (P=0.027). Bone-morphogenetic protein-6, noggin and sclerostin alone could not predict the development of distant metastasis in our patient cohort. However, high level of bone-morphogenetic protein-6 and low level of noggin, or high level of bone-morphogenetic protein-6 and low level of both noggin and sclerostin expression in primary prostate cancer significantly predicted development of distant metastasis. The predictive value was still valid when only high-grade prostate cancers were included or when patients with secondary lesion other than bone were excluded. Taken together, these results suggest that a high level of bone-morphogenetic protein-6 signaling, resulting from increased expression of bone-morphogenetic protein-6 and decreased expression of its inhibitors, might promote the development of prostate cancer metastases. Our results also imply the potential use of bone-morphogenetic protein-6, noggin and sclerostin expression together as a prognostic predictor for metastatic progression of prostate cancer.

Id-1 induces proteasome-dependent degradation of the HBX protein.

Id-1 is a member of the HLH protein family that regulates a wide range of cellular processes such as cell proliferation, apoptosis, senescence and overexpression of Id-1 was recently suggested to play roles in the development and progression of different cancers. Previously, Id-1 was shown to physically interact with the viral protein E1A. Meanwhile, Id-1 expression was found to be regulated by several of the virus-encoded proteins, suggesting that Id-1 may be a common cellular target of the viral proteins. Here, we report that Id-1 interacts with the Hepatitis-B virus (HBV)-encoded protein HBX and regulates its stability in hepatocellular carcinoma (HCC) cells. We found that in HCC cells, ectopic Id-1 expression significantly decreased the half-life of the HBX protein, indicating that HBX is destabilized by Id-1. Meanwhile, the Id-1-induced HBX degradation was found to be inhibited by treatment with proteasome inhibitor, suggesting that this process is mediated through the proteasome pathway. Interestingly, while Id-1 did not induce HBX-ubiquitination, we found that removal of all the lysine residues of the HBX protein protects it from the effect of Id-1, indicating that ubiquitination is still required for the Id-1-mediated HBX degradation. Meanwhile, we found that Id-1 binds to the proteasome subunit C8 and facilitates its interaction with the HBX protein and disruption of this interaction completely abolishes the negative effect of Id-1 on HBX protein stability. Taken together, our results demonstrated a novel function of Id-1 in regulating HBX protein stability through interaction with the proteasome.

MAD2 interacts with DNA repair proteins and negatively regulates DNA damage repair.

MAD2 (mitotic arrest deficient 2) is a key regulator of mitosis. Recently, it had been suggested that MAD2-induced mitotic arrest mediates DNA damage response and that upregulation of MAD2 confers sensitivity to DNA-damaging anticancer drug-induced apoptosis. In this study, we report a potential novel role of MAD2 in mediating DNA nucleotide excision repair through physical interactions with two DNA repair proteins, XPD (xeroderma pigmentosum complementation group D) and ERCC1. First, overexpression of MAD2 resulted in decreased nuclear accumulation of XPD, a crucial step in the initiation of DNA repair. Second, immunoprecipitation experiments showed that MAD2 was able to bind to XPD, which led to competitive suppression of binding activity between XPD and XPA, resulting in the prevention of physical interactions between DNA repair proteins. Third, unlike its role in mitosis, the N-terminus domain seemed to be more important in the binding activity between MAD2 and XPD. Fourth, phosphorylation of H2AX, a process that is important for recruitment of DNA repair factors to DNA double-strand breaks, was suppressed in MAD2-overexpressing cells in response to DNA damage. These results suggest a negative role of MAD2 in DNA damage response, which may be accounted for its previously reported role in promoting sensitivity to DNA-damaging agents in cancer cells. However, the interaction between MAD2 and ERCC1 did not show any effect on the binding activity between ERCC1 and XPA in the presence or absence of DNA damage. Our results suggest a novel function of MAD2 by interfering with DNA repair proteins.

Lignans isolated from Campylotropis hirtella (Franch.) Schindl. decreased prostate specific antigen and androgen receptor expression in LNCaP cells.

Accumulating epidemiological data suggest that Asian men have lower incidences of prostate cancer and benign prostate hyperplasia (BPH) compared with American and European populations and may have benefited from their higher intake of phytoestrogens in their diet. However, how these phytochemicals affect prostatic diseases is still unclear. In this study, we isolated six lignans from a plant, Campylotropis hirtella (Franch.) Schindl., which has been used as a folk medicine for treatment of BPH in China, through bioassay guided fractionation. They were dehydrodiconiferyl alcohol (C1), 4-[(-6-hydroxy-2,3-dihydro-1-benzofuran-3-yl)methyl]-5-methoxybenzene-1,3-diol (C2), erythro-guaiacylglycerol-beta-O-4'-coniferyl ether (C3), threo-guaiacylglycerol-beta-O-4'-coniferyl ether (C4), secoisolariciresinol (C5), and prupaside (C6), where C2 was identified as a new lignan analog. Their IC50 values for inhibition of prostate specific antigen (PSA) secretion were 19, 45, 110, 128, 137, and 186 microM, respectively, from C1 to C6 in LNCaP cells. Further study showed that C1-5 down-regulated cellular PSA expression and C1-4 also decreased androgen receptor (AR) expression in LNCaP cells. Furthermore, we investigated the proapoptotic effect of C1 on LNCaP cells. The active forms of caspase 3 associated with the specific proteolysis of poly (ADP-ribose) polymerase (PARP) were detected, and the antiapoptotic protein Bcl-2 was down-regulated after the treatment with C1. These results collectively indicated that these lignans may have chemopreventive or therapeutic actions for prostate cancer through suppressing AR signaling pathway and inducing apoptosis.

Effect of a prodrug of the green tea polyphenol (-)-epigallocatechin-3-gallate on the growth of androgen-independent prostate cancer in vivo.

Epigallocatechin-3-gallate (EGCG) is the major and most potent polyphenol compound of green tea that has been shown to have anticancer effects against various types of cancers. In this study, in addition to the EGCG compound, a synthetic derivative, the peracetate of EGCG (EGCG-P), was used to investigate the inhibitory effects on growth of androgen-independent prostate cancer in vivo. The advantage of EGCG-P is that it may act as a prodrug, leading to higher bioavailability than EGCG itself. The aim of our study was to compare the differences between EGCG and EGCG-P on their inhibitory effect on androgen-independent prostate cancer, CWR22R, xenograft model in nude mice. The mice were administrated daily with solvent dimethyl sulfoxide, EGCG, and EGCG-P separately through intraperitoneal injection for 20 days. Tumor volume and body weight of nude mice were recorded daily. Serum prostate-specific antigen (PSA) levels were also measured before and after the treatment. The effects of both EGCG and EGCG-P on tumor cell proliferation were assessed by immunohistochemical (IHC) method using antibodies against Ki-67 and proliferating cell nuclear antigen. The apoptotic effect was evaluated by IHC against B-cell non-Hodgkin lymphoma-2 and terminal deoxynucleotidyl transferase dUTP nick-end labeling assay by in situ apoptosis detection kit. Moreover, the potential suppression of angiogenesis by EGCG and EGCG-P on prostate cancer was examined by IHC against CD31. Our results revealed that treatment of EGCG and EGCG-P compounds suppressed the growth of CWR22R xenografts without causing any detectable side effects in nude mice. The suppression of growth of the tumor was correlated with the decrease of serum PSA level together with the reduction in tumor angiogenesis and an increase in apoptosis on prostate cancer cells. The results showed that treatment of EGCG and EGCG-P inhibited tumor growth and angiogenesis while promoting apoptosis of the prostate cancer cells in vivo. Our results suggest that EGCG-P may be a more stable and useful compound for increasing the therapeutic anticancer effects in androgen-independent prostate cancer.

Inactivation of ID-1 gene induces sensitivity of prostate cancer cells to chemotherapeutic drugs.

Resistance to anticancer drugs is one of the major reasons of treatment failure for androgen-independent prostate cancer (PC). Increase in expression of Id-1 has been reported in several types of advanced cancer including PC. It has been suggested that overexpression of Id-1 may provide an advantage for cancer cell survival and thus inactivation of Id-1 may be able to increase the susceptibility of cancer cells to apoptosis. In this study, using small RNA interfering (siRNA) technology, we inactivated the Id-1 gene in two androgen-independent PC cell lines, DU145 and PC3, and investigated whether down-regulation of Id-1 could lead to increased sensitivity of these PC cells to a commonly used anticancer drug, taxol (Tx). Our results showed that inactivation of Id-1 by siId-1 resulted in decrease in both colony forming ability and cell viability in prostate cancer cells after Tx treatment. Furthermore, the siId-1 induced sensitization to Tx was associated with activation of apoptotic pathway. In addition, c-Jun N-terminal kinase (JNK), one of the common pathways responsible for Tx-induced apoptosis, was also activated in the si-Id-1 transfected cells. Inhibition of JNK activity by a specific inhibitor, SP600125, blocked the siId-1-induced sensitivity to Tx. These results indicate that increased Id-1 expression in PC cells may play a protective role against apoptosis, and down-regulation of Id-1 may be a potential target to increase sensitivity of Tx-induced apoptosis in PC cells.

TWIST modulates prostate cancer cell-mediated bone cell activity and is upregulated by osteogenic induction.

TWIST, a helix-loop-helix transcription factor, is highly expressed in many types of human cancer. We have previously found that TWIST confers prostate cancer cells with an enhanced metastatic potential through promoting epithelial-mesenchymal transition (EMT) and a high TWIST expression in human prostate cancer is associated with an increased metastatic potential. The predilection of prostate cancer cells to metastasize to bone may be due to two interplaying mechanisms (i) by increasing the rate of bone remodeling and (ii) by undergoing osteomimicry. We further studied the role of TWIST in promoting prostate cancer to bone metastasis. TWIST expression in PC3, a metastatic prostate cancer cell line, was silenced by small interfering RNA and we found that conditioned medium from PC3 with lower TWIST expression had a lower activity on stimulating osteoclast differentiation and higher activity on stimulating osteoblast mineralization. In addition, we found that these effects were, at least partly, associated with TWIST-induced expression of dickkopf homolog 1 (DKK-1), a factor that promotes osteolytic metastasis. We also examined TWIST and RUNX2 expressions during osteogenic induction of an organ-confined prostate cancer cell, 22Rv1. We observed increased TWIST and RUNX2 expressions upon osteogenic induction and downregulation of TWIST through short hairpin RNA reduced the induction level of RUNX2. In summary, our results suggest that, in addition to EMT, TWIST may also promote prostate cancer to bone metastasis by modulating prostate cancer cell-mediated bone remodeling via regulating the expression of a secretory factor, DKK-1, and enhancing osteomimicry of prostate cancer cells, probably, via RUNX2.

Mitotic checkpoint defects in human cancers and their implications to chemotherapy.

The mitotic checkpoint, also known as spindle assembly checkpoint, is to ensure accurate chromosome segregation by inducing mitotic arrest when errors occur in the spindle structure or in the alignment of the chromosomes on the spindle. Loss of mitotic checkpoint control is a common event in human cancer cells, which is thought to be responsible for chromosome instability frequently observed in cancer cells. Several reports have shown that cells with a defective mitotic checkpoint are more resistant to several types of anticancer drugs from microtubule disruptors to DNA damaging agents. In addition, inactivation of key mitotic checkpoint proteins such as BUB (budding uninhibited by benzimidazole) and MAD (mitotic arrest deficient ) is influential in drug resistance in mitotic checkpoint defective cancer cells. The mitotic checkpoint has also been linked to DNA damage response and a defective mitotic checkpoint confers cancer cells resistance to certain DNA damaging anticancer drugs. This review presents recent evidence on mitotic checkpoint defects in human cancers and their association with resistance to anticancer drugs. In addition, the clinical importance and potential therapeutic implications of targeting the mitotic checkpoint to reverse drug resistance in cancer cells are also discussed.

Identification of a novel inhibitor of differentiation-1 (ID-1) binding partner, caveolin-1, and its role in epithelial-mesenchymal transition and resistance to apoptosis in prostate cancer cells.

Recently, ID-1 (inhibitor of differentiation/DNA binding) is suggested as an oncogene and is reported to promote cell proliferation, invasion, and survival in several types of human cancer cells through multiple signaling pathways. However, how Id-1 interacts with these pathways and the immediate downstream effectors of the Id-1 protein are not known. In this study, using a yeast two-hybrid screening technique, we identified a novel Id-1-interacting protein, caveolin-1 (Cav-1), a cell membrane protein, and a positive regulator of cell survival and metastasis in prostate cancer. Using an immunoprecipitation method, we found that the helix-loop-helix domain of the Id-1 protein was essential for the physical interaction between Id-1 and Cav-1. In addition, we also demonstrated that the physical interaction between Id-1 and Cav-1 played a key role in the epithelial-mesenchymal transition and increased cell migration rate as well as resistance to taxol-induced apoptosis in prostate cancer cells. Furthermore, our results revealed that this effect was regulated by Id-1-induced Akt activation through promoting the binding activity between Cav-1 and protein phosphatase 2A. Our study demonstrates a novel Id-1 binding partner and suggests a molecular mechanism that mediates the function of Id-1 in promoting prostate cancer progression through activation of the Akt pathway leading to cancer cell invasion and resistance to anticancer drug-induced apoptosis.

Role of p14ARF in TWIST-mediated senescence in prostate epithelial cells.

Recently, TWIST, a basic helix-loop-helix transcription factor, is suggested to be an oncogene because of its over-expression in many types of human cancer and its positive role in promoting cell survival. The aim of this study was to investigate the role of TWIST on the growth of human epithelial cells. Using two immortalized human prostate epithelial cell lines, we demonstrated that inactivation of TWIST by small RNA technology led to the promotion of cellular senescence and growth arrest, suggesting that TWIST plays a key role in the continuous proliferation of immortalized cells. Over-expression of TWIST, in contrast, resulted in suppression of cellular senescence in response to genotoxic damage and promotion of cell proliferation with DNA damage accumulation, indicating that TWIST promotes genomic instability. In addition, we also found that the TWIST-mediated cellular senescence was regulated through its negative effect on p14(ARF) and subsequent suppression of MDM2/p53 and Chk1/2 DNA damage response pathways. Our results suggest that over-expression of TWIST results in down-regulation of p14(ARF), which leads to the impairment of DNA damage checkpoint in response to genotoxic stress. This negative effect of TWIST on DNA damage response facilitates uncontrolled cell proliferation with genomic instability and tumorigenesis in non-malignant cells.

Increased Id-1 expression is significantly associated with poor survival of patients with prostate cancer.

The levels of Id-1 (inhibitor of DNA binding or inhibitor of cell differentiation) expression in a series of prostate cell lines and in an archival set of prostate tissues were examined. Western blot analysis showed that the level of Id-1 expressed in the androgen sensitive cell line LNCaP was 1.2 +/- 0.2 times that detected in the benign cell line PNT-2. The level of Id-1 increased further to 1.8 +/- 0.2 and 2.9 +/- 0.3 in the androgen-insensitive cell lines Du-145 and PC-3, respectively. Immunohistochemical staining with Id-1 antibody performed on 113 cases of prostate tissues showed that among the 7 normal cases, 6 (86%) stained either negative or weakly positive whereas only 1 (14%) stained moderately positive. Among the 36 benign prostatic hyperplasia (BPH) samples, 34 (94%) stained either negative or weakly positive; only 1 (3%) stained moderately and 1 (3%) stained strongly. Of the 70 carcinomas, 8 (11.5%) stained weakly, 34 (48.5%) stained moderately, and 28 (40%) stained strongly positive. The intensity of Id-1 staining in carcinomas was significantly stronger than that detected in the normal prostate and BPH (chi(2) test, P < .001) and it was significantly increased as the increasing malignancy of carcinomas measured by Gleason score (chi(2) test, P < .001). The intensity of Id-1 staining was partially associated with the levels of prostate-specific antigen, but not related to the level of androgen receptor. Kaplan-Meier survival curve analysis showed that, similar to Gleason scores, overexpression of Id-1 was significantly associated with the reduced length of patient survival (log-rank test, P = .01). These results suggest that Id-1 is a useful prognostic marker to predict the outcomes of patients with prostate cancer.