Inhibition of colonization and cell-matrix adhesion after nm23-H1 transfection of human prostate carcinoma cells

Regulation of the metastasis suppressor Nm23-H1 by tumor viruses

Metastasis is the most common cause of cancer mortality. To increase the survival of patients, it is necessary to develop more effective methods for treating as well as preventing metastatic diseases. Recent advancement of knowledge in cancer metastasis provides the basis for development of targeted molecular therapeutics aimed at the tumor cell or its interaction with the host microenvironment. Metastasis suppressor genes (MSGs) are promising targets for inhibition of the metastasis process. During the past decade, functional significance of these genes, their regulatory pathways, and related downstream effector molecules have become a major focus of cancer research. Nm23-H1, first in the family of Nm23 human homologues, is a well-characterized, anti-metastatic factor linked with a large number of human malignancies. Mounting evidence to date suggests an important role for Nm23-H1 in reducing virus-induced tumor cell motility and migration. A detailed understanding of the molecular association between oncogenic viral antigens with Nm23-H1 may reveal the underlying mechanisms for tumor virus-associated malignancies. In this review, we will focus on the recent advances to our understanding of the molecular basis of oncogenic virus-induced progression of tumor metastasis by deregulation of Nm23-H1.

TGF-β1 regulates the invasive and metastatic potential of mucoepidermoid carcinoma cells

BACKGROUND

Patients with mucoepidermoid carcinoma exhibit poor long-term prognosis because of the lack of therapeutic strategies that effectively block tumor progression. We have previously characterized the Ms cells as a highly metastatic mucoepidermoid carcinoma cell line that expresses high levels of transforming growth factor β1 (TGF-β1). Here, we studied the effect of suppressing TGF-β1 by RNA silencing on the invasive and metastatic potential of mucoepidermoid carcinoma.

METHODS

Cell motility, substratum adhesion, and transmembrane invasion were estimated by migration, matrigel adhesion, and matrigel invasion assay. Matrix metalloproteinase (MMP)-2 and MMP-9 activity were determined using gelatin gel zymography. Balb/c nu/nu nude mice lung metastatic model was used to test the metastatic ability of the Ms cells. Lung metastatic tumors were experimentally induced by mice tail vein inoculation of cancer cells.

RESULTS

TGF-β1 silencing inhibits cell motility, substratum adhesion, and transmembrane invasion. In vivo, a significant decrease in lung metastasis was observed when mice received tail vein injections of TGF-β1-silenced mucoepidermoid carcinoma cells, as compared to controls.

CONCLUSION

These results unveil a critical role for TGF-β1 in the progression of mucoepidermoid carcinomas and suggest that patients with this malignancy may benefit from therapeutic inhibition of the effectors of the TGF-β1 pathway.

Metastasis suppressor KAI1/CD82 attenuates the matrix adhesion of human prostate cancer cells by suppressing fibronectin expression and β1 integrin activation

KAI1/CD82, a tetraspanin membrane protein functions as a metastasis suppressor in many types of human cancers and has been shown to regulate cell adhesion properties. In the present study, we investigated the underlying mechanism of KAI1/CD82-mediated changes in cell adhesion to the extracellular matrix using human prostate cancer cells. We found that high KAI1/CD82 expression attenuated short-term cell adhesion to uncoated- or fibronectin-coated plates. Moreover, high KAI1/CD82 expression generated an extracellular environment unfavorable for cell adhesion as compared to low KAI1/CD82 expression, suggesting KAI1/CD82-dependent regulation of extracellular matrix (ECM) molecule(s) expression and/or secretion. Among ECM components examined, fibronectin exhibited decreased expression and secretion in high KAI1/CD82-expressing cells. Furthermore, high KAI1/CD82 expression interfered with the activation of β (1) integrin at the cell surface while total β (1) integrin levels remained unchanged, concomitant with reduced formation of focal adhesion complex and decreased bundling of actin filaments. Finally, high KAI1/CD82 expression significantly retarded cell motility in a scratch wound assay. Taken together, our results strongly suggest that KAI1/CD82 attenuates the activation of β (1) integrin, and thereby down-regulates outside-in signaling of β (1) integrin, leading to the reduction of focal adhesion formation and fibronectin expression/secretion, which subsequently interferes with cell adhesion properties and motility.

Metastasis suppressors in human benign prostate, intraepithelial neoplasia, and invasive cancer: their prospects as therapeutic agents

Despite advances in diagnosis and treatment of prostate cancer, development of metastases remains a major clinical challenge. Research efforts are dedicated to overcome this problem by understanding the molecular basis of the transition from benign cells to prostatic intraepithelial neoplasia (PIN), localized carcinoma, and metastatic cancer. Identification of proteins that inhibit dissemination of cancer cells will provide new perspectives to define novel therapeutics. Development of antimetastatic drugs that trigger or mimic the effect of metastasis suppressors represents new therapeutic approaches to improve patient survival. This review focuses on different biochemical and cellular functions of metastasis suppressors known to play a role in prostate carcinogenesis and progression. Ten putative metastasis suppressors implicated in prostate cancer are discussed. CD44s is decreased in both PIN and cancer; Drg-1, E-cadherin, KAI-1, RKIP, and SSeCKS show similar expression between benign epithelia and PIN, but are downregulated in invasive cancer; whereas, maspin, MKK4, Nm23 and PTEN are upregulated in PIN and downregulated in cancer. Moreover, the potential role of microRNA in prostate cancer progression, the understanding of the cellular distribution and localization of metastasis suppressors, their mechanism of action, their effect on prostate invasion and metastasis, and their potential use as therapeutics are addressed.

L-carnosine inhibits metastasis of SK-Hep-1 cells by inhibition of matrix metaoproteinase-9 expression and induction of an antimetastatic gene, nm23-H1

Antioxidants have been suggested to inhibit the expression of matrix metalloproteinases (MMPs), especially MMP-9, which plays a critical role in tumor metastasis. Because of its antioxidant activity and the ability to chelate divalent cations, L-carnosine (LC) was tested for inhibition of MMP-9 in a highly invasive hepatocarcinoma, SK-Hep-1 cells. We found that LC (50-1,000 microM) did not directly inhibit the activity of MMP-9 in a cell-free system. However, LC significantly inhibited the expression and activity of MMP-9 protein in SK-Hep-1 cells [inhibitory concentration of 50% (IC(50))| = 105 and 63 muM, respectively). Whereas LC did not inhibit the viability of SK-Hep-1 cells at concentrations up to 1,000 microM within 3 days of incubation, this dipeptide significantly inhibited cell migration (IC(50) = 82 microM) and invasion (IC(50) = 113 microM). LC significantly (P < 0.05) and dose dependently enhanced the expression of an antimetastatic gene, nonmetastatic cells 1, protein (nm23)-H1, at both protein and messenger ribonucleic acid (mRNA) levels. MMP-9 activity inversely correlated significantly with the expression of protein (r(2) = 0.77, P < 0.001) and mRNA (r(2) = 0.65, P < 0.001) of nm23-H1 in LC-treated cells. Thus, LC can inhibit the migration and invasion of SK-Hep-1 cells, and the effect is likely associated with upregulation of nm23-H1 and downregulation of MMP-9 expression.

Nm23-H1 suppresses metastasis by inhibiting expression of the lysophosphatidic acid receptor EDG2

Nm23-H1 transcriptionally down-regulates expression of the lysophosphatidic acid receptor EDG2 and this down-regulation is critical for Nm23-H1-mediated motility suppression in vitro. We investigated the effect of altered EDG2 expression on Nm23-H1-mediated metastasis suppression in vivo. Clonal MDA-MB-435-derived tumor cell lines transfected with Nm23-H1 together with either a vector control or EDG2 had similar anchorage-dependent and anchorage-independent growth rates in vitro. However, a 45- and 300-fold inhibition of motility and invasion (P < 0.0001), respectively, was observed in Nm23-H1/vector lines, whereas coexpression of EDG2 restored activity to levels observed in the parental line. Using fluorescently labeled cells and ex vivo microscopy, the capacity of these cells to adhere, arrest, extravasate, and survive in the murine lung over a 24-h time course was measured. Only 5% of Nm23-H1/vector-transfected cells were retained in the murine lung 6 h following tail vein injection; coexpression of EDG2 enhanced retention 8- to 13-fold (P < 0.01). In a spontaneous metastasis assay, the primary tumor size of Nm23-H1/vector and Nm23-H1/EDG2 clones was not significantly different. However, restoration of EDG2 expression augmented the incidence of pulmonary metastasis from 51.9% to 90.4% (P = 2.4 x 10(-5)), comparable with parental MDA-MB-435 cells. To determine the relevance of this model system to human breast cancer, a cohort of breast carcinomas was stained for Nm23-H1 and EDG2 and a statistically significant inverse correlation between these two proteins was revealed (r = -0.73; P = 0.004). The data indicate that Nm23-H1 down-regulation of EDG2 is functionally important to suppression of tumor metastasis.

Human nonmetastatic clone 23 type 1 gene suppresses migration of cervical cancer cells and enhances the migration inhibition of fungal immunomodulatory protein from Ganoderma tsugae

The authors investigate the effects of human nonmetastatic clone 23 type 1 (nm23-H1 ) gene and fungal immunomodulatory protein-Ganoderma tsugae (FIP-gts) on the metastatic potential of cervical cancer cells and assess whether nm23-H1 can influence the action of FIP-gts using cell migration and invasion assays and gelatin zymography. The nm23-H1 gene was stably transfected into Caski cells, which lacked nm23-H1 expression. The results show that nm23-H1 stably transfected Caski cells exhibit reduced cell migration but no change of cell invasion and matrix metalloproteinase (MMP)-2 and -9 activities. FIP-gts reduced cell migration in SiHa and nm23-H1 transfected Caski cells more significantly compared with Caski cells and reduced invasion in Caski and nm23-H1-transfected Caski cells, but it exerted no influence on MMP-2 and MMP-9 activities in them. Conclusively, the nm23-H1 gene suppresses cervical cancer cell migration but not invasion and activities of MMP-2 and MMP-9 and enhances the inhibition of FIP-gts upon migration.

Nm23-H1 homologs suppress tumor cell motility and anchorage independent growth

Nm23-H1 suppresses metastasis, as well as in vitro cell motility, invasion and anchorage independent growth, in a variety of cancer models. Eight human homologs of Nm23 have been identified that share 26-88% identity with the prototype Nm23-H1. Here, we examine the potential of its homologs, -H2, DR-, -H4 and -H5, to inhibit in vitro correlates of metastasis in two highly metastatic human cell lines, MDA-MB-435 and MDA-MB-231. The metastatic cells were transfected with mammalian expression constructs containing the genes encoding for Nm23-H1, -H2, DR-, -H4 and -H5 and the resultant transfectants were analyzed by Boyden chamber motility and soft agar colonization assays. Nm23-H1 suppressed motility by 3.3- and 1.5-fold in MDA-MB-435 and MDA-MB-231 cells, respectively and inhibited anchorage independent growth in soft agar by 2.9- and 1.9-fold, respectively. None of the -H1 homologs were capable of suppressing motility in MDA-MB-435 cells, but in MDA-MB-231 cells, -H2 inhibited motility by 3-fold upon overexpression. When anchorage independent growth was assessed, -H2, -H4 and -H5 suppressed growth from 1.2- to 2.0-fold in both cell lines. Given their ability to suppress anchorage independent growth, Nm23-H1 homologs -H2, -H4 and -H5 may have some capacity to suppress metastasis. Motility suppression appears to be cell context dependent, but sequence disparities between -H1/H2 and the other family members may reveal regions critical for this inhibitory phenotype. Similarly, sequence differences between DR-Nm23 and its homologs may be important for anchorage independent growth suppression.

Nm23-H1 suppresses tumor cell motility by down-regulating the lysophosphatidic acid receptor EDG2

Exogenous overexpression of the metastasis suppressor gene Nm23-H1 reduces the metastatic potential of multiple types of cancer cells and suppresses in vitro tumor cell motility and invasion. Mutational analysis of Nm23-H1 revealed that substitution mutants P96S and S120G did not inhibit motility and invasion. To elucidate the molecular mechanism of Nm23-H1 motility suppression, expression microarray analysis of an MDA-MB-435 cancer cell line overexpressing wild-type Nm23-H1 was done and cross-compared with expression profiles from lines expressing the P96S and S120G mutants. Nine genes, MET, PTN, SMO, FZD1, L1CAM, MMP2, NETO2, CTGF, and EDG2, were down-regulated by wild-type but not by mutant Nm23-H1 expression. Reduced expression of these genes coincident with elevated Nm23-H1 expression was observed in human breast tumor cohorts, a panel of breast carcinoma cell lines, and hepatocellular carcinomas from control versus Nm23-M1 knockout mice. The functional significance of the down-regulated genes was assessed by transfection and in vitro motility assays. Only EDG2 overexpression significantly restored motility to Nm23-H1-suppressed cancer cells, enhancing motility by 60-fold in these cells. In addition, silencing EDG2 expression with small interfering RNA reduced the motile phenotype of metastatic breast cancer cells. These data suggest that Nm23-H1 suppresses metastasis, at least in part, through down-regulation of EDG2 expression.

Nm23-H1: a metastasis-associated gene

The protein product of nm23-H1 gene has activity of nucleoside diphosphate (NDP) kinase, which catalyzes the phosphorylation of nucleoside diphosphates to the corresponding nucleoside triphosphates. Reductions in nm23 expression have been significantly associated with aggressive behavior in melanoma, breast, colon, and gastric carcinomas. On the contrary, high levels of nm23 gene expression are noted in the advanced stage of thyroid carcinomas and associated with significant reductions in survival for neuroblastoma and osteosarcoma patients. Although expression of nm23/NDP kinase is divergent in various malignant tumors, its reduced expression seems to be related to increased metastatic potential in most carcinoma types. However, it is hypothesized that nm23 may play a tissue-specific role, and that different regulatory mechanisms may act in different tumors. In ovarian carcinoma, nm23-H1/NDP kinase may be correlated with some clinicopathologic characteristics. In cervical cancer, nm23-H1 is probably involved in cervical carcinogenesis and correlated with some aggressive parameters. Overexpression of nm23-H1 protein may indicate poor survival for cervical cancer patients. Other than histidine 118 residue (amino acid sequence 118: histidine) concerned with NDP kinase activity of nm23-H1, serine 120 (amino acid sequence 120: serine) related activity of histidine-dependent protein phosphotransfer was recently reported to be responsible for its biological suppressive effects. To inhibit metastatic potential, nm23-H1 is also demonstrated to co-immunoprecipitate the kinase suppressor of Ras and phosphorylate it, and therefore reduce activation of the extracellular signal-regulated kinase mitogen-activated protein kinase pathway in response to signaling.

PRUNE and NM23-M1 expression in embryonic and adult mouse brain

A genetic interaction between PRUNE and NM23/NDPK has been postulated in Drosophila melanogaster. Many have focused on Drosophila for the genetic combination between PRUNE "knock down" and AWD/NM23 fly mutants bearing the P97S mutation (K-pn, Killer of PRUNE mutation). We postulated a role for PRUNE-NM23 interactions in vertebrate development, demonstrating a physical interaction between the human PRUNE and NM23-H1 proteins, and partially characterizing their functional significance in cancer progression. Here, we present an initial analysis towards the functional characterization of the PRUNE-NM23 interaction during mammalian embryogenesis. Our working hypothesis is that PRUNE, NM23-H1 and their protein-protein interaction partners have important roles in mammalian brain development and adult brain function. Detailed expression analyses from early mouse brain development to adulthood show significant co-expression of these two genes during embryonic stages of brain development, especially focusing on the cortex, hippocampus, midbrain and cerebellum. We hypothesize that their abnormal expression results in an altered pathway of activation, influencing protein complex formation and its protein partner interactions in early embryogenesis. In the adult brain, their function appears concentrated towards their enzyme activities, wherein biochemical variations can result in brain dysfunction.

A splice variant of CD99 increases motility and MMP-9 expression of human breast cancer cells through the AKT-, ERK-, and JNK-dependent AP-1 activation signaling pathways

The CD99 gene encodes two distinct transmembrane proteins by alternative splicing of its transcript. To examine the effects of two CD99 isoforms on the invasive phenotypes of breast cancer cells, MDA-MB-231 and MCF-7 human breast cancer cell lines were stably transfected with CD99 cDNAs encoding the major wild-type form (type I) or a minor splice variant (type II). As a result, expression of CD99 type II, but not type I, markedly elevated the motility, binding to fibronectin, MMP-9 expression, and invasiveness of MDA-MB-231 and MCF-7 breast cancer cells. In MDA-MB-435 breast cancer cells expressing both CD99 type I and type II, invasion-related cellular activities were inhibited by the transfection of small interfering RNA (siRNA) targeted to CD99 type II. Meanwhile, CD99 type II-induced MMP-9 expression in MDA-MB-231 cells was shown to be mediated by the binding of AP-1 factors to the MMP-9 gene promoter. Gel shift assay revealed that ligation of CD99 type II with antibody resulted in the binding of JunD to the AP-1 site of the MMP-9 promoter region. Initiation of CD99 type II signaling by antibody ligation increased expression of JunD and FosB AP-1 factors, along with phosphorylation of Src, Akt, p38 MAPK, ERK, and JNK. Knockdown of JunD and FosB by siRNA transfection abolished the positive effects of CD99 type II on the motility and MMP-9 expression of MDA-MB-231 cells. Increased expression of JunD and FosB as well as elevated cell motility and MMP-9 expression by CD99 type II ligation were also abrogated by inhibitors, dominant-negative forms, and siRNAs for Akt1, ERK1/2, and JNK1 but not for p38 MAPK. These results suggest that expression of a splice variant of CD99 contributes to the invasive ability of human breast cancer cells by up-regulating AP-1-mediated gene expression through the Akt-dependent ERK and JNK signaling pathways.

Reduction of invasion in human fibrosarcoma cells by ribosomal protein S3 in conjunction with Nm23-H1 and ERK

RpS3 is a component of the 40S ribosomal subunit of eukaryotes and also plays a role as a base damage endonuclease. Nm23-H1 encodes nucleoside diphosphate kinase A and acts as a suppressor of metastasis in certain human tumors. RpS3 interacted with nm23-H1, and the two proteins were colocalized in the cell periphery and cytoplasm. The 190th leucine of rpS3, and the 118th histidine and the 120th serine of nm23-H1 play key roles in the interaction of two proteins, respectively. The expression of rpS3 reduced the secretion of MMP-9 and the invasive potential in HT1080 cells. Additionally, the phosphorylated ERK was reduced by the expression of rpS3. In MCF7 cells, where the ERK pathway is inactivated and MMPs are not secreted and the ERK pathway can be activated by PMA, the PMA-induced ERK phosphorylation was reduced by the expression of rpS3. However, the L190A mutant of rpS3, which did not interact with nm23-H1, did not inhibit the invasive potential, the secretion of MMP-9, and the activation of the ERK pathway in HT1080 cells and PMA-activated MCF7 cells. These results suggest that rpS3 inhibits invasion via blocking the ERK pathway and MMP-9 secretion; the results also suggest that the interaction of rpS3 and nm23-H1 appears to be critical in this inhibition.

Lycopene inhibits cell migration and invasion and upregulates Nm23-H1 in a highly invasive hepatocarcinoma, SK-Hep-1 cells

The carotenoid lycopene has been associated with decreased risks of several types of cancer, such as prostate cancer and hepatoma. Tumor metastasis is the most important cause of cancer death. Although lycopene was shown to inhibit metastasis, the mechanism underlying this action is not well understood. Here, we tested the possibility that lycopene may inhibit cancer cell metastasis by upregulating the expression of nm23-H1, a metastasis suppressor gene, in SK-Hep-1 cells, a highly invasive hepatoma cell line, and we determined migration and invasion activities and the expression of nm23-H1 protein and mRNA. We showed that lycopene inhibited SK-Hep-1 migration and invasion in a bell-shaped manner, with the highest effect at 5 micromol/L (91 and 63% inhibition for migration and invasion, respectively; P < 0.05). At the same test level (10 micromol/L), lycopene was much more effective than beta-carotene in reducing cell invasion (by approximately 870%). In contrast to the effects on migration and invasion, lycopene enhanced nm23-H1 expression at both the protein and mRNA levels; the effects were also bell shaped, and at 5 micromol/L, lycopene enhanced nm23-H1 protein and mRNA expressions by 220 +/- 33 and 153 +/- 22% (P < 0.01), respectively. These bell-shaped effects of lycopene may be related to autoxidation of lycopene at elevated concentrations (> or =10 micromol/L). Significant correlations existed between nm23-H1 protein expression and migration (r2= 0.78, P < 0.001) and between nm23-H1 protein expression and invasion (r2= 0.84, P < 0.001) in lycopene-treated SK-Hep-1 cells. We conclude that lycopene has significant antimigration and anti-invasion activity, and that this effect is associated with its induction of nm23-H1 expression.

Genetic and epigenetic alterations of the candidate tumor-suppressor gene MYO18B, on chromosome arm 22q, in colorectal cancer

Allelic imbalance (AI) on chromosome arm 22q has been detected in 20%-40% of colorectal cancers, suggesting that this chromosome arm has a tumor-suppressor gene involved in colorectal carcinogenesis. Recently, we isolated a candidate tumor-suppressor gene, MYO18B, at 22q12.1, that is deleted, mutated, and hypermethylated in more than 50% of lung cancers. In the present study, we analyzed genetic and epigenetic alterations of the MYO18B gene in colorectal cancers. AI at the MYO18B locus was detected in 16 of 43 (40%) informative cases. Mutations of the MYO18B gene were detected in 2 of 11 (18%) cell lines and 1 of 47 (2%) surgical specimens. Nine of 11 (82%) cell lines showed reduced MYO18B expression, which was restored in all 9 by treatment with 5-aza-2'-deoxycytidine and/or trichostatin A (TSA). Although hypermethylation of the promoter CpG island for MYO18B was not detected, a significant correlation was observed between the level of MYO18B expression and the level of acetylation of histones H3 and H4 in 6 cell lines with and without TSA treatment. Thus, it was suggested that MYO18B is inactivated in a considerable fraction of colorectal cancers by several mechanisms, especially silencing by histone deacetylation and/or AI. Furthermore, restoration of MYO18B expression in colorectal cancer cell lines HT29 and DLD-1 suppressed anchorage-independent growth, whereas it did not affect the growth rate in vitro. These results suggest that genetic and epigenetic inactivation of the MYO18B gene play an important role in colorectal carcinogenesis.

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.

nm23-H1 reduces in vitro cell migration and the liver metastatic potential of colon cancer cells by regulating myosin light chain phosphorylation

The nm23-H1 gene is known as a potential metastasis suppressor gene in various types of carcinomas. However, the role of nm23-H1 in colorectal carcinoma still remains controversial and the cellular mechanisms by which its protein may modulate the metastatic phenotype are not yet known. We transfected nm23-H1 cDNA into the human colon cancer cell line, HT-29, to test the effects and cellular biological mechanism of nm23 protein in colon cancer. We found that nm23-H1 strongly inhibited the liver metastasis of HT-29 cells in nude mice and inhibited the epidermal growth factor (EGF)-induced cell migration in vitro. Furthermore, we clarified the regulation of the myosin light chain (MLC) phosphorylation by nm23-H1, which has been demonstrated as having potential role in cell migration.

Point mutations affecting the oligomeric structure of Nm23-H1 abrogates its inhibitory activity on colonization and invasion of prostate cancer cells

In order to identify Nm23-H1's structural motifs influencing its metastasis-inhibitory activity, we transfected DU 145 human prostate carcinoma cells with the expression vector encoding the Nm23-H1 protein with mutations at the following amino acids: serine-44, a phosphorylation site; proline-96, a site corresponding to the k-pn mutation that causes developmental defects in Drosophila; and serine-120, a site of mutation in human neuroblastoma and phosphorylation. Significant decrease in colonization in soft agar and invasiveness of DU 145 cells was observed in the wild type nm23-H1 transfectants, and also in the serine-44 and serine-120 to alanine mutant nm23-H1-transfected cell lines. However, the k-pn type proline-96 to serine (P96S) and neuroblastoma type serine-120 to glycine (S120G) mutations of Nm23-H1 abrogated its inhibitory activity on colonization and invasion. Meanwhile, all of the recombinant mutant Nm23-H1 proteins produced in Escherichia coli exhibited NDP kinase activity levels at the wild type protein, although the P96S and S120G mutant proteins exhibited decreased histidine protein kinase activity and autophosphorylation level, respectively. Interestingly, only two of the mutant recombinant Nm23-H1 proteins examined, P96S and S120G, exhibited reduced hexameric and increased dimeric oligomerization relative to the wild type. These correlative data suggest that the metastasis-suppressing activity of Nm23-H1 may depend on its oligomeric structure, but not on its NDP kinase activity.

The metastatic suppressor Nm23-H1 interacts with EBNA3C at sequences located between the glutamine- and proline-rich domains and can cooperate in activation of transcription

Epstein-Barr virus (EBV) is a lymphotrophic herpesvirus infecting most of the world's population. It is associated with a number of human lymphoid and epithelial tumors and lymphoproliferative diseases in immunocompromised patients. Recent studies have shown an in vitro and in vivo interaction between the EBV nuclear antigen 3C (EBNA3C) and the metastatic suppressor Nm23-H1, known to be downregulated in human invasive breast carcinoma. In this study, we have identified the domain of EBNA3C that specifically binds to Nm23-H1. This domain lies within the region comprising amino acids 637 to 675 of EBNA3C flanked by the proline- and glutamine-rich domains. Furthermore, we show that Nm23-H1 activates transcription when fused to the Gal4 DNA-binding domain and is coexpressed with a luciferase reporter construct containing the Gal4 binding sites upstream of a basal promoter. Gal4-Nm23-H1, when tethered to the promoter by binding to the Gal4 DNA binding sequences, consistently activated transcription. The level of activation increased when increasing amounts of Gal4-Nm23-H1 were introduced into the system. Moreover, EBNA3C when cotransfected with Gal4-Nm23-H1 enhanced the transcriptional activity. These results suggest that Nm23-H1 may have intrinsic transcription activities in EBV-infected cells and that this activity can be modulated in the presence of the essential latent antigen EBNA3C.

Epstein-Barr virus nuclear protein EBNA-3C interacts with the human metastatic suppressor Nm23-H1: a molecular link to cancer metastasis

Epstein-Barr virus (EBV) is an oncogenic virus associated with a number of human malignancies including Burkitt lymphoma, nasopharyngeal carcinoma, lymphoproliferative disease and, though still debated, breast carcinoma. A subset of latent EBV antigens is required for mediating immortalization of primary B-lymphocytes. Here we demonstrate that the carboxy-terminal region of the essential latent antigen, EBNA-3C, interacts specifically with the human metastatic suppressor protein Nm23-H1. Moreover, EBNA-3C reverses the ability of Nm23-H1 to suppress the migration of Burkitt lymphoma cells and breast carcinoma cells. We propose that EBNA-3C contributes to EBV-associated human cancers by targeting and altering the role of the metastasis suppressor Nm23-H1.

Nucleoside diphosphate kinase beta (Nm23-R1/NDPKbeta) is associated with intermediate filaments and becomes upregulated upon cAMP-induced differentiation of rat C6 glioma

Nucleoside diphosphate kinases (Nm23/NDPK) are enzymes functional in cell proliferation, differentiation, development, tumor progression, and metastasis. Nevertheless, no consensus exists about the molecular mechanism by which Nm23/NDPK isoforms exert their role in these processes. We investigated the expression of the rat Nm23-R1/NDPKbeta and Nm23-R2/NDPKalpha isoforms, homologues of the human Nm23-H1/NDPK A and Nm23-H2/NDPK B proteins, respectively, upon cAMP-induced differentiation of rat C6 glioma cells and demonstrated a differential interaction with intermediate filaments. Semiquantitative RT-PCR, immunoblotting, and flow cytometry showed a constitutive expression of both Nm23 isoforms. After induction of differentiation in C6 cells with cAMP analogs or isoproterenol, a dose-dependent 2- and 2.5-fold upregulation of the Nm23-R1 mRNA and protein, respectively, was observed. In contrast, the expression of Nm23-R2 remained unchanged. Localization of both isoforms with confocal laser scanning microscopy demonstrated a punctate reticular staining pattern for both Nm23 isoforms in the cytosol and processes of the cells which was particularly intense in the perinuclear region. In addition, while Nm23-R2 was colocalized and coimmunoprecipitated with vimentin in nondifferentiated cells, both isoforms were associated with GFAP in differentiated cells. The significance of these findings in relation to a possible function of Nm23 isoforms in cell proliferation, differentiation, and tumor-associated mechanisms is discussed.

Nm23/nucleoside diphosphate kinase in human cancers

Tumor metastasis is the leading cause of death in cancer patients. From a series of tumor cohort studies, low expression of Nm23/NDP kinase has been correlated with poor patient prognosis and survival, lymph node infiltration, and histopathological indicators of high metastatic potential in a number of cancer types, including mammary and ovarian carcinomas and melanoma. In other tumor types, no correlation has been established. Transfection of Nm23/NDP kinase cDNA into highly metastatic breast, melanoma, prostrate and squamous cell carcinomas, and colon adenocarcinoma cells significantly reduced the metastatic competency of the cells in vivo. In culture, cell motility, invasion, and colonization were inhibited, whereas tumorigenicity and cellular proliferation were not affected, indicating that Nm23/NDP kinase acts as a metastasis suppressor.

Comprehensive analyses of prostate gene expression: convergence of expressed sequence tag databases, transcript profiling and proteomics

Several methods have been developed for the comprehensive analysis of gene expression in complex biological systems. Generally these procedures assess either a portion of the cellular transcriptome or a portion of the cellular proteome. Each approach has distinct conceptual and methodological advantages and disadvantages. We have investigated the application of both methods to characterize the gene expression pathway mediated by androgens and the androgen receptor in prostate cancer cells. This pathway is of critical importance for the development and progression of prostate cancer. Of clinical importance, modulation of androgens remains the mainstay of treatment for patients with advanced disease. To facilitate global gene expression studies we have first sought to define the prostate transcriptome by assembling and annotating prostate-derived expressed sequence tags (ESTs). A total of 55000 prostate ESTs were assembled into a set of 15953 clusters putatively representing 15953 distinct transcripts. These clusters were used to construct cDNA microarrays suitable for examining the androgen-response pathway at the level of transcription. The expression of 20 genes was found to be induced by androgens. This cohort included known androgen-regulated genes such as prostate-specific antigen (PSA) and several novel complementary DNAs (cDNAs). Protein expression profiles of androgen-stimulated prostate cancer cells were generated by two-dimensional electrophoresis (2-DE). Mass spectrometric analysis of androgen-regulated proteins in these cells identified the metastasis-suppressor gene NDKA/nm23, a finding that may explain a marked reduction in metastatic potential when these cells express a functional androgen receptor pathway.