Activation of the tumor metastasis suppressor gene, KAI1, by etoposide is mediated by p53 and c-Jun genes

The Wheel of p53 Helps to Drive the Immune System

The p53 tumor suppressor protein is best known as an inhibitor of the cell cycle and an inducer of apoptosis. Unexpectedly, these functions of p53 are not required for its tumor suppressive activity in animal models. High-throughput transcriptomic investigations as well as individual studies have demonstrated that p53 stimulates expression of many genes involved in immunity. Probably to interfere with its immunostimulatory role, many viruses code for proteins that inactivate p53. Judging by the activities of immunity-related p53-regulated genes it can be concluded that p53 is involved in detection of danger signals, inflammasome formation and activation, antigen presentation, activation of natural killer cells and other effectors of immunity, stimulation of interferon production, direct inhibition of virus replication, secretion of extracellular signaling molecules, production of antibacterial proteins, negative feedback loops in immunity-related signaling pathways, and immunologic tolerance. Many of these p53 functions have barely been studied and require further, more detailed investigations. Some of them appear to be cell-type specific. The results of transcriptomic studies have generated many new hypotheses on the mechanisms utilized by p53 to impact on the immune system. In the future, these mechanisms may be harnessed to fight cancer and infectious diseases.

Synthesis, biological evaluation, and molecular docking of novel hydroxyzine derivatives as potential AR antagonists

Prostate cancer (PCa) is a malignant tumor with a higher mortality rate in the male reproductive system. In this study, the hydroxyazine derivatives were synthesized with different structure from traditional anti-prostate cancer drugs. In the evaluation of in vitro cytotoxicity and antagonistic activity of PC-3, LNCaP, DU145 and androgen receptor, it was found that the mono-substituted derivatives on the phenyl group (4, 6, 7, and 9) displayed strong cytotoxic activities, and compounds 11–16 showed relatively strong antagonistic potency against AR (Inhibition% >55). Docking analysis showed that compounds 11 and 12 mainly bind to AR receptor through hydrogen bonds and hydrophobic bonds, and the structure-activity relationship was discussed based on activity data. These results suggested that these compounds may have instructive implications for drug structural modification in prostate cancer.

Targeting CD82/KAI1 for Precision Therapeutics in Surmounting Metastatic Potential in Breast Cancer

Metastasis is the main cause of mortality in breast cancer patients. There is an unmet need to develop therapies that can impede metastatic spread. Precision oncology has shown great promise for the treatment of cancers, as the therapeutic approach is tailored to a specific group of patients who are likely to benefit from the treatment, rather than the traditional approach of "one size fits all". CD82, also known as KAI1, a glycoprotein belonging to the tetraspanin family and an established metastasis suppressor, could potentially be exploited to hinder metastases in breast cancer. This review explores the prospect of targeting CD82 as an innovative therapeutic approach in precision medicine for breast cancer patients, with the goal of preventing cancer progression and metastasis. Such an approach would entail the selection of a subset of breast cancer patients with low levels of CD82, and instituting an appropriate treatment scheme tailored towards restoring the levels of CD82 in this group of patients. Proposed precision treatment regimens include current modalities of treating breast cancer, in combination with either clinically approved drugs that could restore the levels of CD82, CD82 peptide mimics or non-coding RNA-based therapeutics.

Promoter CpG-Site Methylation of the KAI1 Metastasis Suppressor Gene Contributes to Its Epigenetic Repression in Prostate Cancer

BACKGROUND

Repression of the KAI1 metastasis suppressor gene is closely associated with malignancy and poor prognosis in many human cancer types including prostate cancer. Since gene repression in human cancers frequently results from epigenetic alterations by DNA methylation and histone modifications, we examined whether the KAI1 gene becomes silenced through these epigenetic mechanisms in prostate cancer.

METHODS

KAI1 mRNA and protein levels were determined by RT-PCR and immunoblotting analyses, respectively. Methylation status of the KAI1 promoter DNA in prostate cancer cell lines and tissues was evaluated by methylation-specific PCR analysis of bisulfite-modified genomic DNAs. Methylated CpG sites in the KAI1 promoter were identified by sequencing the PCR clones of the bisulfite-modified KAI1 promoter DNA. KAI1 protein levels in human prostate cancer tissue samples were examined by immunofluorescence staining of the tissues with an anti-KAI1 antibody.

RESULTS

Among the three human prostate cancer cell lines examined, PC3 and DU145 cells exhibited markedly decreased levels of KAI1 mRNA and protein as compared to LNCaP cells, even though the exogenous KAI1 promoter not being methylated was normally functional in all these cell lines. Treatment of the low KAI1-expressing cell lines with a demethylating agent, 5'-aza-2'-deoxycytidine, significantly elevated KAI1 expression levels, implicating the involvement of DNA methylation in KAI1 downregulation. Methylation of CpG islands within the KAI1 promoter region was observed in the low KAI1-expressing cells, but not in the high KAI1-expressing cells. Also, methyl CpG-binding proteins such as MBD2 and MeCP2 were complexed to the KAI1 promoter in the low KAI1-expressing cells. Bisulfite sequencing analysis identified the intensively methylated CpG residues in the KAI1 promoter clones derived from prostate cancer cells and tissues with no or low KAI1 expression. As in prostate cancer cell lines, prostate cancer tissues from patients also displayed a negative association between KAI1 expression levels and methylation status of the KAI1 promoter.

CONCLUSIONS

The present data suggest that the KAI1 gene might be repressed by epigenetic alterations through the promoter CpG-site methylation during prostate cancer progression. This epigenetic mechanism could provide a clue for understanding how the KAI1 gene was silenced in metastatic prostate cancers. Prostate 77: 350-360, 2017. © 2016 Wiley Periodicals, Inc.

The molecular effect of metastasis suppressors on Src signaling and tumorigenesis: new therapeutic targets

A major problem for cancer patients is the metastasis of cancer cells from the primary tumor. This involves: (1) migration through the basement membrane; (2) dissemination via the circulatory system; and (3) invasion into a secondary site. Metastasis suppressors, by definition, inhibit metastasis at any step of the metastatic cascade. Notably, Src is a non-receptor, cytoplasmic, tyrosine kinase, which becomes aberrantly activated in many cancer-types following stimulation of plasma membrane receptors (e.g., receptor tyrosine kinases and integrins). There is evidence of a prominent role of Src in tumor progression-related events such as the epithelial–mesenchymal transition (EMT) and the development of metastasis. However, the precise molecular interactions of Src with metastasis suppressors remain unclear. Herein, we review known metastasis suppressors and summarize recent advances in understanding the mechanisms of how these proteins inhibit metastasis through modulation of Src. Particular emphasis is bestowed on the potent metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1) and its interactions with the Src signaling cascade. Recent studies demonstrated a novel mechanism through which NDRG1 plays a significant role in regulating cancer cell migration by inhibiting Src activity. Moreover, we discuss the rationale for targeting metastasis suppressor genes as a sound therapeutic modality, and we review several examples from the literature where such strategies show promise. Collectively, this review summarizes the essential interactions of metastasis suppressors with Src and their effects on progression of cancer metastasis. Moreover, interesting unresolved issues regarding these proteins as well as their potential as therapeutic targets are also discussed.

JunD Is Required for Proliferation of Prostate Cancer Cells and Plays a Role in Transforming Growth Factor-β (TGF-β)-induced Inhibition of Cell Proliferation

TGF-β inhibits proliferation of prostate epithelial cells. However, prostate cancer cells in advanced stages become resistant to inhibitory effects of TGF-β. The intracellular signaling mechanisms involved in differential effects of TGF-β during different stages are largely unknown. Using cell line models, we have shown that TGF-β inhibits proliferation in normal (RWPE-1) and prostate cancer (DU145) cells but does not have any effect on proliferation of prostate cancer (PC3) cells. We have investigated the role of Jun family proteins (c-Jun, JunB, and JunD) in TGF-β effects on cell proliferation. Jun family members were expressed at different levels and responded differentially to TGF-β treatment. TGF-β effects on JunD protein levels, but not mRNA levels, correlated with its effects on cell proliferation. TGF-β induced significant reduction in JunD protein in RWPE-1 and DU145 cells but not in PC3 cells. Selective knockdown of JunD expression using siRNA in DU145 and PC3 cells resulted in significant reduction in cell proliferation, and forced overexpression of JunD increased the proliferation rate. On the other hand, knockdown of c-Jun or JunB had little, if any, effect on cell proliferation; overexpression of c-Jun and JunB decreased the proliferation rate in DU145 cells. Further studies showed that down-regulation of JunD in response to TGF-β treatment is mediated via the proteasomal degradation pathway. In conclusion, we show that specific Jun family members exert differential effects on proliferation in prostate cancer cells in response to TGF-β, and inhibition of cell proliferation by TGF-β requires degradation of JunD protein.

Identification and validation of genes with expression patterns inverse to multiple metastasis suppressor genes in breast cancer cell lines

Metastasis suppressor genes (MSGs) have contributed to an understanding of regulatory pathways unique to the lethal metastatic process. When re-expressed in experimental models, MSGs block cancer spread to, and colonization of distant sites without affecting primary tumor formation. Genes have been identified with expression patterns inverse to a single MSG, and found to encode functional, druggable signaling pathways. We now hypothesize that common signaling pathways mediate the effects of multiple MSGs. By gene expression profiling of human MCF7 breast carcinoma cells expressing a scrambled siRNA, or siRNAs to each of 19 validated MSGs (NME1, BRMS1, CD82, CDH1, CDH2, CDH11, CASP8, MAP2K4, MAP2K6, MAP2K7, MAPK14, GSN, ARHGDIB, AKAP12, DRG1, CD44, PEBP1, RRM1, KISS1), we identified genes whose expression was significantly opposite to at least five MSGs. Five genes were selected for further analysis: PDE5A, UGT1A, IL11RA, DNM3 and OAS1. After stable downregulation of each candidate gene in the aggressive human breast cancer cell line MDA-MB-231T, in vitro motility was significantly inhibited. Two stable clones downregulating PDE5A (phosphodiesterase 5A), an enzyme involved in the regulation of cGMP-specific signaling, exhibited no difference in cell proliferation, but reduced motility by 47 and 66 % compared to the empty vector-expressing cells (p = 0.01 and p = 0.005). In an experimental metastasis assay, two shPDE5A-MDA-MB-231T clones produced 47-62 % fewer lung metastases than shRNA-scramble expressing cells (p = 0.045 and p = 0.009 respectively). This study demonstrates that previously unrecognized genes are inversely related to the expression of multiple MSGs, contribute to aspects of metastasis, and may stand as novel therapeutic targets.

Vincristine enhances amoeboid-like motility via GEF-H1/RhoA/ROCK/Myosin light chain signaling in MKN45 cells

Background

Anti-cancer drugs are widely used in cancer treatment frequently combined with surgical therapy and/or radiation therapy. Although surgery and radiation have been suggested to facilitate invasion and metastasis of tumor cells in some cases, there is so far little information about the effect of anti-cancer drugs on cellular invasive ability and metastasis. In this study, using four different anti-cancer drugs (vincristine, paclitaxel, cisplatin and etoposide), we examined whether these drugs influence the invasive ability of tumor cells.

Methods

Human gastric adenocarcinoma MKN45 cells were used to evaluate the effect of anti-cancer drugs. After drug treatment, cellular invasive ability was assessed using the Matrigel invasion chamber. Cytoskeletal changes after treatment were examined microscopically with F-actin staining. In addition, we monitored cellular motility in 3D matrigel environment by time-lapse microscopic analysis. The drug-induced activation of RhoA and ROCK was evaluated by pull-down assay and Western blotting using an antibody against phosphorylated myosin light chain (MLC), respectively. Where necessary, a ROCK inhibitor Y27632 and siRNA for guanine nucleotide exchange factor-H1 (GEF-H1) were applied.

Results

Among all drugs tested, only vincristine stimulated the invasive ability of MKN45 cells. Microscopic analysis revealed that vincristine induced the formation of non-apoptotic membrane blebs and amoeboid-like motility. Vincristine significantly enhanced RhoA activity and MLC phosphorylation, suggesting the involvement of RhoA/ROCK pathway in the vincristine-induced cytoskeletal reorganization and cellular invasion. Furthermore, we found that Y27632 as well as the siRNA for GEF-H1, a RhoA-specific activator, attenuated MLC phosphorylation, the formation of membrane blebs and the invasive ability after vincristine treatment.

Conclusions

These results indicate that vincristine activates GEF-H1/RhoA/ROCK/MLC signaling, thereby promoting amoeboid-like motility and the invasive ability of MKN45 cells.

Dissecting the diverse functions of the metastasis suppressor CD82/KAI1

The recent identification of metastasis suppressor genes, the products of which inhibit metastasis but not primary tumor growth, distinguishes oncogenic transformation and tumor suppression from a hallmark of malignancy, the ability of cancer cells to invade sites distant from the primary tumor. The metastasis suppressor CD82/KAI1 is a member of the tetraspanin superfamily of glycoproteins. CD82 suppresses metastasis by multiple mechanisms including inhibition of cell motility and invasion, promotion of cell polarity as well as induction of senescence and apoptosis in response to extracellular stimuli. A common feature of these diverse effects is CD82 regulation of membrane organization as well as protein trafficking and interactions, which affects cellular signaling and intercellular communication.

N-fused imidazoles as novel anticancer agents that inhibit catalytic activity of topoisomerase IIα and induce apoptosis in G1/S phase

On the basis of structures of known topoisomerase II catalytic inhibitors and initial molecular docking studies, bicyclic N-fused aminoimidazoles were predicted as potential topoisomerase II inhibitors. They were synthesized by multicomponent reactions and evaluated against human topoisomerase IIα (hTopoIIα) in decatenation, relaxation, cleavage complex, and DNA intercalation in vitro assays. Among 31 compounds of eight different bicyclic scaffolds, it was found that imidazopyridine, imidazopyrazole, and imidazopyrazine with suitable substituents exhibited potent inhibition of catalytic activity of hTopoIIα while not showing DNA intercalation. Molecular docking studies and molecular dynamics (MD) simulation analysis, ATPase-kinetics and ATP-dependent plasmid relaxation assay revealed the catalytic mode of inhibition of the title compounds plausibly by blocking the ATP-binding site. N-Fused aminoimidazoles showed potent anticancer activities in kidney and breast cancer cell lines, low toxicity to normal cells, relatively higher potency compared to etoposide and 5-fluorouracil in kidney cancer cell lines, and potent inhibition in cell migration. These compounds were found to exert apoptotic effect in G1/S phase.

KAI1 gene is engaged in NDRG1 gene-mediated metastasis suppression through the ATF3-NFkappaB complex in human prostate cancer

NDRG1 and KAI1 belong to metastasis suppressor genes, which impede the dissemination of tumor cells from primary tumors to distant organs. Previously, we identified the metastasis promoting transcription factor, ATF3, as a downstream target of NDRG1. Further analysis revealed that the KAI1 promoter contained a consensus binding motif of ATF3, suggesting a possibility that NDRG1 suppresses metastasis through inhibition of ATF3 expression followed by activation of the KAI1 gene. In this report, we found that ectopic expression of NDRG1 was able to augment endogenous KAI1 gene expression in prostate cancer cell lines, whereas silencing NDRG1 was accompanied with significant decrease in KAI1 expression in vitro and in vivo. In addition, our results of ChIP analysis indicate that ATF3 indeed bound to the promoter of the KAI1 gene. Importantly, our promoter-based analysis revealed that ATF3 modulated KAI1 transcription through cooperation with other endogenous transcription factor as co-activator (ATF3-JunB) or co-repressor (ATF3-NFκB). Moreover, loss of KAI1 expression significantly abrogated NDRG1-mediated metastatic suppression in vitro as well as in a spontaneous metastasis animal model, indicating that KA11 is a functional downstream target of the NDRG1 pathway. Our result of immunohistochemical analysis showed that loss of NDRG1 and KAI1 occurs in parallel as prostate cancer progresses. We also found that a combined expression status of these two genes serves as a strong independent prognostic marker to predict metastasis-free survival of prostate cancer patients. Taken together, our result revealed a novel regulatory network of two metastasis suppressor genes, NDRG1 and KAI1, which together concerted metastasis-suppressive activities through an intrinsic transcriptional cascade.

MKK4 suppresses metastatic colonization by multiple highly metastatic prostate cancer cell lines through a transient impairment in cell cycle progression

Metastatic dissemination in prostate cancer is often early, but not all cancer cells form clinical metastases. Map kinase kinase 4 (MKK4) suppresses metastasis in a preclinical prostate cancer model. We hypothesize that MKK4 will specifically inhibit metastatic colonization through impaired proliferation. Three highly metastatic rat prostate cancer cell lines (AT6.1, Mat-Lu and AT3.1) were employed. Stably over-expressing HA-MKK4 or vector control lines were injected into immunocompromised mice. These experiments validated that HA-MKK4 specifically affects metastatic colonization and increases survival. Median survival (days) with HA-MKK4 vs. vector was 42 vs. 28 (p < 0.0001) for AT6.1, 25 vs. 19 (p < 0.0001) for Mat-Lu and 27 vs. 20 (p < 0.0001) for AT3.1. HA-MKK4 suppresses colonization within 14 days post dissemination, after which exponential proliferation resumes. Although overt metastases retain HA-MKK4, it is inactive within these lesions. Nonetheless, metastasis-derived cell lines were shown to retain functional HA-MKK4 and like their parental HA-MKK4 line are suppressed for experimental metastasis formation in vivo. Disseminated AT6.1-HA-MKK4 cells were analyzed and were found to have an alteration in cell cycle. Specifically, there was an accumulation of cells in G1-phase (p = 0.024) and decrease in S-phase (p = 0.037) compared with vector. In multiple prostate cancer lines, HA-MKK4 suppresses an early step in metastatic colonization. These data support a model in which MKK4 activation at the metastatic site causes a cell-cycle arrest, which is eventually overcome despite presence of functional HA-MKK4. Further studies will specifically interrogate the regulation of MKK4 activation within the metastatic microenvironment and the down-stream molecular events critical for metastasis suppression.

Metastasis suppressor genes at the interface between the environment and tumor cell growth

The molecular mechanisms and genetic programs required for cancer metastasis are sometimes overlapping, but components are clearly distinct from those promoting growth of a primary tumor. Every sequential, rate-limiting step in the sequence of events leading to metastasis requires coordinated expression of multiple genes, necessary signaling events, and favorable environmental conditions or the ability to escape negative selection pressures. Metastasis suppressors are molecules that inhibit the process of metastasis without preventing growth of the primary tumor. The cellular processes regulated by metastasis suppressors are diverse and function at every step in the metastatic cascade. As we gain knowledge into the molecular mechanisms of metastasis suppressors and cofactors with which they interact, we learn more about the process, including appreciation that some are potential targets for therapy of metastasis, the most lethal aspect of cancer. Until now, metastasis suppressors have been described largely by their function. With greater appreciation of their biochemical mechanisms of action, the importance of context is increasingly recognized especially since tumor cells exist in myriad microenvironments. In this chapter, we assemble the evidence that selected molecules are indeed suppressors of metastasis, collate the data defining the biochemical mechanisms of action, and glean insights regarding how metastasis suppressors regulate tumor cell communication to-from microenvironments.

1'-Acetoxychavicol acetate suppresses angiogenesis-mediated human prostate tumor growth by targeting VEGF-mediated Src-FAK-Rho GTPase-signaling pathway

Cancer therapeutic agents that are safe, effective and affordable are urgently needed. We describe that 1'-acetoxychavicol acetate (ACA), a component of Siamese ginger (Languas galanga), can suppress prostate tumor growth by largely abrogating angiogenesis. ACA suppressed vascular endothelial growth factor (VEGF)-induced proliferation, migration, adhesion and tubulogenesis of primary cultured human umbilical vascular endothelial cells (HUVECs) in a dose-dependent manner. ACA also inhibited VEGF-induced microvessel sprouting from aortic rings ex vivo and suppressed new vasculature formation in Matrigel plugs in vivo. We further demonstrated that the mechanisms of this chavicol were to block the activation of VEGF-mediated Src kinase, focal adhesion kinase (FAK) and Rho family of small guanosine triphosphatases (GTPases) (Rac1 and Cdc42 but not RhoA) in HUVECs. Furthermore, treatment of human prostate cancer cells (PC-3) with ACA resulted in decreased cell viability and suppression of angiogenic factor production by interference with dual Src/FAK kinases. After subcutaneous administration to mice bearing human prostate cancer PC-3 xenografts, ACA (6 mg/kg/day) remarkably inhibited tumor volume and tumor weight and decreased levels of Src, CD31, VEGF and Ki-67. As indicated by immunohistochemistry and TUNEL analysis, microvessel density and cell proliferation were also dramatically suppressed in tumors from ACA-treated mice. Taken together, our findings suggest that ACA targets the Src-FAK-Rho GTPase pathway, leading to the suppression of prostate tumor angiogenesis and growth.

Learning therapeutic lessons from metastasis suppressor proteins

Metastasis suppressor proteins regulate multiple steps in the metastatic cascade, including cancer cell invasion, survival in the vascular and lymphatic circulation, and colonization of distant organ sites. Understanding the biology of metastasis suppressors provides valuable mechanistic insights that may translate to therapeutic opportunities. Several reports have explored novel strategies for restoring metastasis suppressor function, including gene transfer, induction of previously suppressed gene expression and exogenous administration of gene product. Pathways activated downstream of metastasis suppressor loss can also be targeted. Although none of these strategies are yet in routine clinical use, several are being tested preclinically and in clinical trials.

Controlling cell surface dynamics and signaling: how CD82/KAI1 suppresses metastasis

The recent identification of metastasis suppressor genes, uniquely responsible for negatively controlling cancer metastasis, are providing inroads into the molecular machinery involved in metastasis. While the normal function of a few of these genes is known; the molecular events associated with their loss that promotes tumor metastasis is largely not understood. KAI1/CD82, whose loss is associated with a wide variety of metastatic cancers, belongs to the tetraspanin family. Despite intense scrutiny, many aspects of how CD82 specifically functions as a metastasis suppressor and its role in normal biology remain to be determined. This review will focus on the molecular events associated with CD82 loss, the potential impact on signaling pathways that regulate cellular processes associated with metastasis, and its relationship with other metastasis suppressor genes.

Metastasis suppressors and their roles in breast carcinoma

Metastasis remains the most deadly aspect of cancer and still evades direct treatment. Clinically and experimentally, primary tumor development and metastasis are distinct processes-locally growing tumors can progress without the development of metastases. The discovery of endogenous molecules that exclusively inhibit metastasis suggests that metastasis is an amenable therapeutic target. By definition, metastasis suppressors inhibit metastasis without inhibiting tumorigenicity and are thus distinct from tumor suppressors. As the biology underlying functional mechanisms of metastasis suppressors becomes clearer, it is evident that metastasis suppressors could be harnessed as direct drug targets, prognostic markers, and to understand the fundamental biology of the metastatic process. Metastasis suppressors vary widely in their cellular localization: they are found in every cellular compartment and some are secreted. In general, metastasis suppressors appear to regulate selectively how cells respond to exogenous signals, by affecting signaling cascades which regulate downstream gene expression. This review briefly summarizes current functional and biochemical data on metastasis suppressors implicated in breast cancer. We also present a schematic integrating known mechanisms for these metastasis suppressors highlighting potential targets for therapeutic intervention.

Tumor-endothelial cell interactions: therapeutic potential

Metastasis is the primary cause of death in cancer patients. However, the molecular mechanism of the metastatic process is poorly understood because it involves multiple steps with a high degree of complexity. A critical step for successful establishment of secondary colonization is the hematogenous dissemination of malignant cells. During this process, the attachment of cancer cells to the endothelial cells on microvasculature is considered to be an essential step and many adhesion molecules as well as chemokines have been found to be involved in this process. This interaction of cancer-endothelial cell is considered not only to determine the physical site of metastasis, but also to provide the necessary anchorage to facilitate tumor cell extravasation. However, recent evidence indicates that this interaction also serves as a host defense mechanism and hinders the process of metastasis. The tumor metastases suppressor gene, KAI1, has been known to block metastatic process without affecting the primary tumor growth, and this protein has been found to be able to bind to the chemokine receptor, Duffy antigen receptor for chemokines (DARC), which is expressed on endothelial cells. Importantly, this interaction markedly induces senescence of tumor cells. This novel finding is not only significant in the context of molecular dissection of metastatic process but also in the therapeutic implication to develop drugs inhibiting metastasis.

3,3'-diindolylmethane is a novel topoisomerase IIalpha catalytic inhibitor that induces S-phase retardation and mitotic delay in human hepatoma HepG2 cells

Epidemiological evidence suggests that high consumption of Brassica genus vegetables, such as broccoli, cabbage, and Brussels sprouts, is very effective in reducing the risks of several types of cancers. 3,3'-Diindolylmethane (DIM), one of the most abundant and biologically active dietary compounds derived from Brassica genus vegetables, displays remarkable antitumor activity against several experimental tumors. In the present study, we demonstrate for the first time that DIM is a novel catalytic topoisomerase IIalpha inhibitor. In supercoiled DNA relaxation assay and kinetoplast DNA decatenation assay, DIM strongly inhibited DNA topoisomerase IIalpha and also partially inhibited DNA topoisomerases I and IIbeta. DIM did not stabilize DNA cleavage complex and did not prevent etoposide-induced DNA cleavage complex formation. Further experiments showed that DIM inhibited topoisomerase IIalpha-catalyzed ATP hydrolysis, which is a necessary step for the enzyme turnover. In cultured human hepatoma HepG2 cells, DIM blocked DNA synthesis and mitosis in a concentration-dependent manner, which was consistent with the outcome of topoisomerase inhibition in these cell-cycle phases. Our results identified a new mode of action for this intriguing dietary component that might be exploited for therapeutic development.

KAI1/CD82, a tumor metastasis suppressor

Tetraspanin KAI1/CD82 is a wide-spectrum tumor metastasis suppressor. KAI1/CD82 suppresses tumor metastasis by primarily inhibiting cancer cell motility and invasiveness. In tetraspanin-enriched microdomain, KAI1/CD82 associates with the proteins important for cell migration such as cell adhesion molecule, growth factor receptor, and signaling molecule. Likely, KAI1/CD82 down-regulates the functions of these motility-related proteins to inhibit cell migration. The loss of KAI1/CD82 expression in invasive and metastatic cancers is due to a complex, epigenetic mechanism that probably involves transcription factors such as NFkappaB, p53, and beta-catenin.

KAI1 promoter activity is dependent on p53, junB and AP2: evidence for a possible mechanism underlying loss of KAI1 expression in cancer cells

A molecular mechanism to explain reduced KAI1 expression in invasive and metastatic tumour cells remains elusive. In this report, we extend an earlier study in bladder cells to confirm that a 76 bp region of the KAI1 promoter (residues -922 to -847), with binding motifs for p53, AP1 and AP2, is required for high level activity of a KAI1 reporter in prostate cancer cell lines. Gel shift and supershift experiments supported binding of p53, junB and heterodimers of AP2alpha/AP2gamma or AP2beta/AP2gamma to this sequence. Introduction of mutations into specific motifs demonstrated an essential requirement for p53 and junB to reporter activity, and that functional synergy between these two factors enhanced activity. A further elevation of reporter activity required AP2. Roles of individual p53, junB and AP2 proteins, as well as functional synergy between p53 and junB, were confirmed in transfection experiments. Western blotting analysis showed that an absence of wild-type p53, and/or a loss of junB and AP2 protein expression, correlated with downregulation of KAI1 mRNA levels in a series of prostate cancer cell lines. A loss of p53 function and/or expression of junB, combined with reduced expression of specific AP2 proteins may underly downregulated KAI1 expression in tumour cells.

Metastasis suppressor genes: a role for raf kinase inhibitor protein (RKIP)

The metastatic cascade is a complicated process that involves many steps from gain of the metastatic phenotype in the primary tumor cells through establishment of macroscopic tumor at the distant target organ. A group of genes, termed metastasis suppressor genes (MSG), encode for proteins that inhibit various steps of the metastatic cascade. Accordingly, loss of MSG promotes the metastatic phenotype. Although several MSG have been identified, the mechanisms through which they enhance metastasis are not clearly defined. Gene array analysis of a low metastatic LNCaP prostate cancer cell line compared to its highly metastatic derivative C4-2B prostate cancer cell line revealed decreased expression of raf kinase inhibitor protein (RKIP) in the C4-2B cell line. RKIP blocks the activation of several signaling pathways including MEK, G-proteins and NFkappaB. Immunohistochemical analysis of prostate cancer primary tumors and metastases revealed that RKIP protein expression was decreased in metastases. Restoration of RKIP expression in the C4-2B cell line diminished metastasis in a murine model. These results demonstrate that RKIP is a MSG. Loss of RKIP enhanced both angiogenesis and vascular invasion, and protected against apoptosis. These findings suggest that targeting the RKIP pathway may diminish the metastatic cascade. However, challenges exist as to the best method to target RKIP expression. Restoration of RKIP expression in all cancer cells in vivo is challenging. A plausible strategy is to use small molecules that target proteins in signaling pathways that are dysregulated due to loss of RKIP.

Down-regulation of KAI1/CD82 protein expression in oral cancer correlates with reduced disease free survival and overall patient survival

Oral Squamous Cell Carcinoma (OSCC) is a common malignancy. Treatment failure is mainly due to loco-regional disease recurrence. KAI1 is a newly discovered metastasis suppressor gene. Fifty-seven patients with primary OSCC underwent surgery alone or surgery and adjuvant radiotherapy. Immunohistochemical evaluation of KAI1/CD82 and p53 proteins was carried out on specimen obtained at surgery. Within neoplastic fields, KAI1/CD82 expression was downregulated and negative in 42/57 (73.7%) cases. p53 expression was positive in 26/57 (45.6%) cases. No correlation was noted between KAI1/CD82 and p53 expression or clinicopathological parameters. Univariate and multivariate Cox proportional hazard models showed a correlation between KAI1/CD82 expression with disease free survival (P = 0.01, P = 0.009) and overall survival (P = 0.04, P = 0.053) respectively.

Downregulation of KAI1 mRNA in localised prostate cancer and its bony metastases does not correlate with p53 overexpression

Recent data have proposed that transcription of the KAI1 metastasis suppressor gene is directly mediated by p53 and that loss of KAI1 expression in advanced prostate cancer is simply due to loss of p53 function after mutation. To investigate this possibility, we have examined KAI1 mRNA (by in situ hybridisation) and p53 protein expression (by immunohistochemistry) as an indicator of wildtype or mutant p53, in a series of 77 paraffin-embedded prostate tissue samples, including post-mortem normal prostates (2), benign prostatic hyperplasia (10), localised cancer (grades 4-6, 25; grades 7-9, 21) and prostate-derived bony metastases (19). Overall, we confirmed that expression of KAI1 mRNA decreased from normal tissue, through localised cancer to bony metastases (P=0.055, tending to significance), while levels of p53 staining significantly increased with cancer progression (P=0.046). These were consistent with the possibility that loss of p53 function might be responsible for loss of KAI1 mRNA. However, by close examination of KAI1 and p53 in adjacent tissue sections, we found no correlation between decreased levels of KAI1 mRNA and overexpression of p53 protein (P=0.497). In addition, high levels of KAI1 mRNA could be identified in samples irrespective of p53 staining. Our data suggest that mutation of p53 is independent of the loss of KAI1 mRNA, and do not support a role for p53 in regulating the expression of KAI1.

ATP- and UTP-activated P2Y receptors differently regulate proliferation of human lung epithelial tumor cells

The involvement of P2Y receptors, which are activated by extracellular nucleotides, in proliferative regulation of human lung epithelial cells is unclear. Here we show that extracellular ATP and UTP stimulate bromodeoxyuridine (BrdU) incorporation into epithelial cell lines. The nucleotide efficacy profile [ATP = ADP > UDP >or= UTP > adenosine >or= 2-methylthioadenosine-5'-diphosphate, with alpha,beta-methylene adenosine 5'-triphosphate, 2',3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate, AMP, UMP, and ATPalphaS inactive] and PCR analysis indicate involvement of P2Y2 and P2Y6 receptors. The signal transduction pathway, which, via the P2Y2 receptor, transmits the proliferative activity of ATP or UTP in A549 cells downstream of phospholipase C, depends on Ca2+/calmodulin-dependent protein kinase II and nuclear factor-kappaB, but not on protein kinase C. Signaling does not involve the mitogen-activated protein kinases extracellular signal-regulated kinases-1 and -2, the phosphatidylinositol 3-kinase pathway, or Src kinases. Thus nucleotides regulate proliferation of human lung epithelial cells by a novel pathway. The stimulatory effect of UTP, but not ATP, in A549 cells is attenuated by preincubation with interleukin-1beta and interleukin-6, but not tumor necrosis factor-alpha. This indicates an important role for the pyrimidine-activated P2Y receptor in the inflammatory response of lung epithelia. ATP antagonizes the antiproliferative effect of the anticancer drugs paclitaxel and etoposide, whereas it enhances the activity of cisplatin about fourfold. Thus pathways activated by extracellular nucleotides differentially control proliferation of lung epithelial tumor cells.

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Expression of tetraspanins in human lung cancer cells: frequent downregulation of CD9 and its contribution to cell motility in small cell lung cancer

Small cell lung cancer (SCLC) invades locally and metastasizes distantly extremely early when compared with nonsmall cell lung cancer (NSCLC). The underlying molecular mechanisms, however, have not been elucidated. Accumulating evidence suggests that downregulation of several members of tetraspanins is associated with progression of solid tumors, thus indicating poor prognosis. Here we screened 30 lung cancer cell lines for expression of tetraspanins, CD9, CD63, CD81, CD82, CD151, and NAG-2. Flow cytometry revealed that, among these proteins, CD9 is broadly expressed in NSCLC lines, but is absent or highly reduced in most SCLC lines (P<0.0001). Using the Boyden chamber and videomicroscopic cell motility assays, we showed that stable transfection of CD9 into an SCLC line, OS3-R5, reduced cell motility on fibronectin. Furthermore, by transient transfection of green fluorescent protein (GFP)-tagged CD9 into three other SCLC lines, we observed that SCLC cells expressing GFP-CD9 were uniformly less motile than untransfected cells. CD9 or GFP-CD9 was associated with beta1 integrins and distributed at the tumor cell periphery and cell-cell contacts, suggesting that CD9 modifies beta1 integrin function to reduce motility. These findings suggest that low expression of CD9 may contribute to the highly invasive and metastatic phenotype of SCLC.

Identification of regulatory regions within the KAI1 promoter: a role for binding of AP1, AP2 and p53

The mechanism underlying loss of KAI1 gene expression in invasive and metastatic tumour cells is unknown. A possible scenario could involve altered expression or function of protein factors normally involved in regulating KAI1 transcription. To explore this possibility, we have initiated a study to characterise regulatory elements of the KAI1 promoter, using as a model, two bladder cancer cell lines (BL13 and HT1376) expressing high levels of endogenous KAI1 messenger RNA (mRNA). Transfection experiments using reporter plasmids with progressive KAI1 promoter deletions, identified a 76 bp region upstream of the transcription initiation site which contained putative binding motifs for AP2, p53 and AP1, as essential for reporter activity. DNA-binding studies using nuclear extracts from both cell lines, showed that AP1 and AP2 formed specific complexes with oligonucleotides containing KAI1 promoter motifs. Mutation of either motif abrogated reporter activity and abolished specific complex formation. In BL13 cells (endogenous wildtype p53), but not in HT1376 cells (endogenous mutant p53), mutation of the p53-binding motif also abrogated reporter activity and abolished specific complex formation in gel shift assays. These data suggested that a combination of AP2, p53 and AP1 binding to specific motifs within the KAI1 promoter might be required for high level promoter activity and that loss of expression or function of these factors might contribute to loss of KAI1 expression in invasive tumours and tumour cell lines. To explore this possibility, we examined levels of these proteins in nuclear extracts of BL13 and HT1376, as well as three bladder cancer cell lines which expressed little or no KAI1 mRNA. Our data suggested that a loss of KAI1 mRNA was not simply due to absence of AP2, AP1 or p53 expression.

Relationship between expression of KAI1 metastasis suppressor gene, mRNA levels and p53 in human bladder and prostate cancer cell lines

The molecular basis for the loss of KAI1 expression in invasive and metastatic tumors and tumor cell lines is not understood. Recently, identification of a sequence with homology to the consensus p53-binding motif in the promoter of the KAI1 metastasis suppressor gene, has led to a proposal that transcriptional regulation by p53 controls expression of KAI1, and that a dramatic down-regulation of KAI1 mRNA levels in invasive tumors and many tumor cell lines, is directly due to loss of p53 function. We have tested this hypothesis by assessing KAI1 mRNA levels in a series of 22 cell lines derived from bladder and prostate cancers, in which we confirmed the p53 gene sequence and characterized the functional status of the endogenous p53 protein. We anticipated that cell lines expressing p53 capable of transactivation should express high levels of KAI1 mRNA compared with cell lines expressing defective p53, or which were p53-null. KAI1 mRNA levels were determined by northern analysis using a full-length KAI1 cDNA probe, and varied widely between cell lines examined. However, there was no association between these levels and p53 status. Furthermore, transfection of representative cell lines with wild-type p53, or exposure to DNA damaging agents, had no effect on KAI1 mRNA levels. Our data suggest that p53 is not a major factor regulating levels of KAI1 mRNA in bladder and prostate cancer cell lines.

Reciprocal control of expression of mRNAs for osteoclast differentiation factor and OPG in osteogenic stromal cells by genistein: evidence for the involvement of topoisomerase II in osteoclastogenesis

Osteoclast-like cells, in cocultures with mouse spleen cells and clonal osteogenic stromal ST2 cells, are formed from spleen cells with monocyte/macrophage lineage in response to a combination of osteoclast differentiation factor (RANKL) and OPG, a decoy receptor for RANKL, produced by ST2 cells in response to 1alpha,25-dihydroxyvitamin D(3). Treatment of ST2 cells with the natural isoflavonoid genistein for 6 h before coculture with spleen cells inhibited the formation of tartrate-resistant acid phosphatase-positive osteoclast-like cells. When we measured levels of RANKL mRNA in ST2 cells, we found that genistein decreased the level of this mRNA. By contrast, the level of OPG mRNA was enhanced by genistein. Genistein is a specific inhibitor of topoisomerase II (topo II) and an inhibitor of protein tyrosine kinase, as well as being a potent phytoestrogen. To characterize the mode of action of genistein, we examined the effects of an inactive form of genistein (daidzein), 17beta-estradiol, inhibitors of topo II, and inhibitors of tyrosine kinases on the formation of tartrate-resistant acid phosphatase-positive osteoclast-like cells. Among the compounds tested, two inhibitors of topo II, amsacrine and etoposide, attenuated the formation of osteoclast-like cells via reciprocal regulation of the expression of mRNAs for RANKL and OPG in ST2 cells, acting similarly to genistein. Our findings indicate that genistein might inhibit the formation of osteoclast-like cells via inhibition of the activity of topo II, suggesting the novel possibility that topo II might play an important role in osteoclastogenesis.