Decreased expression of nucleoside diphosphate kinase alpha isoform, an nm23-H2 gene homolog, is associated with metastatic potential of rat mammary-adenocarcinoma cells

Mechanisms of action of NME metastasis suppressors - a family affair

Metastatic progression is regulated by metastasis promoter and suppressor genes. NME1, the prototypic and first described metastasis suppressor gene, encodes a nucleoside diphosphate kinase (NDPK) involved in nucleotide metabolism; two related family members, NME2 and NME4, are also reported as metastasis suppressors. These proteins physically interact with members of the GTPase dynamin family, which have key functions in membrane fission and fusion reactions necessary for endocytosis and mitochondrial dynamics. Evidence supports a model in which NDPKs provide GTP to dynamins to maintain a high local GTP concentration for optimal dynamin function. NME1 and NME2 are cytosolic enzymes that provide GTP to dynamins at the plasma membrane, which drive endocytosis, suggesting that these NMEs are necessary to attenuate signaling by receptors on the cell surface. Disruption of NDPK activity in NME-deficient tumors may thus drive metastasis by prolonging signaling. NME4 is a mitochondrial enzyme that interacts with the dynamin OPA1 at the mitochondria inner membrane to drive inner membrane fusion and maintain a fused mitochondrial network. This function is consistent with the current view that mitochondrial fusion inhibits the metastatic potential of tumor cells whereas mitochondrial fission promotes metastasis progression. The roles of NME family members in dynamin-mediated endocytosis and mitochondrial dynamics and the intimate link between these processes and metastasis provide a new framework to understand the metastasis suppressor functions of NME proteins.

The dosage-dependent effect exerted by the NM23-H1/H2 homolog NDK-1 on distal tip cell migration in C. elegans

Abnormal regulation of cell migration and altered rearrangement of the cytoskeleton are fundamental properties of metastatic cells. The first identified metastasis suppressor NM23-H1, which displays nucleoside-diphosphate kinase (NDPK) activity is involved in these processes. NM23-H1 inhibits the migratory and invasive potential of some cancer cells. Correspondingly, numerous invasive cancer cell lines (eg, breast, colon, oral, hepatocellular carcinoma, and melanoma) display low endogenous NM23 levels. In this review, we summarize mechanisms, which are linked to the anti-metastatic activity of NM23. In human cancer cell lines NM23-H1 was shown to regulate cytoskeleton dynamics through inactivation of Rho/Rac-type GTPases. The Drosophila melanogaster NM23 homolog abnormal wing disc (AWD) controls tracheal and border cell migration. The molecular function of AWD is well characterized in both processes as a GTP supplier of Shi/Dynamin whereby AWD regulates the level of chemotactic receptors on the surface of migrating cells through receptor internalization, by its endocytic function. Our group studied the role of the sole group I NDPK, NDK-1 in distal tip cell (DTC) migration in Caenorhabditis elegans. In the absence of NDK-1 the migration of DTCs is incomplete. A half dosage of NDPK as present in ndk-1 (+/-) heterozygotes results in extra turns and overshoots of migrating gonad arms. Conversely, an elevated NDPK level also leads to incomplete gonadal migration owing to a premature stop of DTCs in the third phase of migration, where NDK-1 acts. We propose that NDK-1 exerts a dosage-dependent effect on the migration of DTCs. Our data derived from DTC migration in C. elegans is consistent with data on AWD's function in Drosophila. The combined data suggest that NDPK enzymes control the availability of surface receptors to regulate cell-sensing cues during cell migration. The dosage of NDPKs may be a coupling factor in cell migration by modulating the efficiency of receptor recycling.

Functional Relationship and Gene Ontology Classification of Breast Cancer Biomarkers

Breast cancer is a complex disease that still imposes a significant healthcare burden on women worldwide. The etiology of breast cancer is not known but significant advances have been made in the area of early detection and treatment. The advent of advanced molecular biology techniques, mapping of the human genome and availability of high throughput genomic and proteomic strategies opens up new opportunities and will potentially lead to the discovery of novel biomarkers for early detection and prognostication of breast cancer. Currently, many biomarkers, particularly the hormonal and epidermal growth factor receptors, are being utilized for breast cancer prognosis. Unfortunately, none of the biomarkers in use have sufficient diagnostic, prognostic and/or predictive power across all categories and stages of breast cancer. It is recognized that more useful information can be generated if tumors are interrogated with multiple markers. But choosing the right combination of biomarkers is challenging, because 1) multiple pathways are involved, 2) up to 62 genes and their protein products are potentially involved in breast cancer-related mechanisms and 3) the more markers evaluated, the more the time and cost involved. This review summarizes the current literature on selected biomarkers for breast cancer, discusses the functional relationships, and groups the selected genes based on a Gene Ontology™ classification.

NME2 reduces proliferation, migration and invasion of gastric cancer cells to limit metastasis

Gastric cancer is one of the most common malignancies and has a high rate of metastasis. We hypothesize that NME2 (Nucleoside Diphosphate Kinase 2), which has previously been considered as an anti-metastatic gene, plays a role in the invasiveness of gastric cancer cells. Using a tissue chip technology and immunohistochemistry, we demonstrated that NME2 expression was associated with levels of differentiation of gastric cancer cells and their metastasis into the lymph nodes. When the NME2 gene product was over-expressed by ;in vitro stable transfection, cells from BGC823 and MKN45 gastric cancer cell lines had reduced rates of proliferation, migration, and invasion through the collagen matrix, suggesting an inhibitory activity of NME2 in the propagation and invasion of gastric cancer. NME2 could, therefore, severe as a risk marker for gastric cancer invasiveness and a potential new target for gene therapy to enhance or induce NME2 expression.

Regulatory functions of Nm23-H2 in tumorigenesis: insights from biochemical to clinical perspectives

Substantial effort has been directed at elucidating the functions of the products of the Nm23 tumor metastasis suppressor genes over the past two decades, with the ultimate goal of exploring their translational potentials in changing cancer patients' outcomes. Much attention has been focused on the better-known Nm23-H1, but despite having high sequence similarity, Nm23-H2 functions differently in many aspects. Besides acting as a metastasis suppressor, compelling data suggest that Nm23-H2 may modulate various tumor-associated biological events to enhance tumorigenesis in human solid tumors and hematological malignancies. Linkage to tumorigenesis may occur through the ability of Nm23-H2 to regulate transcription, cell proliferation, apoptosis, differentiation, and telomerase activity. In this review, we examine the linkages of Nm23-H2 to tumorigenesis in terms of its biochemical and structural properties and discuss its potential role in various tumor-associated events.

Insights into the biology and prevention of tumor metastasis provided by the Nm23 metastasis suppressor gene

Metastatic disease is the major cause of death among cancer patients. A class of genes, named metastasis suppressors, has been described to specifically regulate the metastatic process. The metastasis suppressor genes are downregulated in the metastatic lesion compared to the primary tumor. In this review, we describe the body of research surrounding the first metastasis suppressor identified, Nm23. Nm23 overexpression in aggressive cancer cell lines reduced their metastatic potential in vivo with no significant reduction in primary tumor size. A complex mechanism of anti-metastatic action is unfolding involving several known Nm23 enzymatic activities (nucleotide diphosphate kinase, histidine kinase, and 3'-5' exonuclease), protein-protein interactions, and downstream gene regulation properties. Translational approaches involving Nm23 have progressed to the clinic. The upregulation of Nm23 expression by medroxyprogesterone acetate has been tested in a phase II trial. Other approaches with significant preclinical success include gene therapy using traditional or nanoparticle delivery, and cell permeable Nm23 protein. Recently, based on the inverse correlation of Nm23 and LPA1 expression, a LPA1 inhibitor has been shown to both inhibit metastasis and induce metastatic dormancy.

Effect of inhibition of the lysophosphatidic acid receptor 1 on metastasis and metastatic dormancy in breast cancer

BACKGROUND

Previous studies identified the human nonmetastatic gene 23 (NME1, hereafter Nm23-H1) as the first metastasis suppressor gene. An inverse relationship between Nm23-H1 and expression of lysophosphatidic acid receptor 1 gene (LPAR1, also known as EDG2 or hereafter LPA1) has also been reported. However, the effects of LPA1 inhibition on primary tumor size, metastasis, and metastatic dormancy have not been investigated.

METHODS

The LPA1 inhibitor Debio-0719 or LPA1 short hairpinned RNA (shRNA) was used. Primary tumor size and metastasis were investigated using the 4T1 spontaneous metastasis mouse model and the MDA-MB-231T experimental metastasis mouse model (n = 13 mice per group). Proliferation and p38 intracellular signaling in tumors and cell lines were determined by immunohistochemistry and western blot to investigate the effects of LPA1 inhibition on metastatic dormancy. An analysis of variance-based two-tailed t test was used to determine a statistically significant difference between treatment groups.

RESULTS

In the 4T1 spontaneous metastasis mouse model, Debio-0719 inhibited the metastasis of 4T1 cells to the liver (mean = 25.2 liver metastases per histologic section for vehicle-treated mice vs 6.8 for Debio-0719-treated mice, 73.0% reduction, P < .001) and lungs (mean = 6.37 lesions per histologic section for vehicle-treated mice vs 0.73 for Debio-0719-treated mice, 88.5% reduction, P < .001), with no effect on primary tumor size. Similar results were observed using the MDA-MB-231T experimental pulmonary metastasis mouse model. LPA1 shRNA also inhibited metastasis but did not affect primary tumor size. In 4T1 metastases, but not primary tumors, expression of the proliferative markers Ki67 and pErk was reduced by Debio-0719, and phosphorylation of the p38 stress kinase was increased, indicative of metastatic dormancy.

CONCLUSION

The data identify Debio-0719 as a drug candidate with metastasis suppressor activity, inducing dormancy at secondary tumor sites.

Mechanisms of non-metastatic 2 (NME2)-mediated control of metastasis across tumor types

Non-metastatic 23 [NM23/nucleoside diphosphate kinases (NDPK)] genes are the first discovered metastasis suppressor genes. More than two decades of research has demonstrated their roles in a variety of biological processes with NME1 and NME2 being most studied in the context of metastasis suppression. Although NME1 and NME2 share >85% homology at amino acid level, they show redundant as well as unique molecular functions. Phenotypic analyses of knockout (KO) mice for NM23 members (NDPK-A, B) and compound KO (A as well as B) showed requirement of both proteins in hematopoiesis suggesting shared functions in development disease. Several reviews have discussed NME1, however the role of NME2 appears to be relatively less understood in the context of metastasis suppression. Here, we focus on NME2 and by meta-analysis of gene expression from multiple tumor types, and survey of in vivo and vitro studies, suggest the possibility that NME2 may be one of the key factors in metastasis. This along with the relevance of normal physiological functions of NME2 in the context of metastasis is discussed. We further examined the genetic and epigenetic features of NME2 and NME1 gene promoters and found aspects of transcription control that could be unique to NME2/NME1. Findings on signaling pathways and small molecules which regulate the expression of NME2 that could be therapeutically important are also discussed.

Altered gene and protein expression by Nm23-H1 in metastasis suppression

Metastasis suppressor genes (MSG) are characterized by their ability to inhibit the formation of metastasis, while not affecting the growth of the primary tumor in vivo. Nm23-H1, the first MSG to be characterized, has been shown to alter both gene and protein expression in cancer cells. Recently, microarray expression profiling revealed that Nm23-H1 downregulated EDG2, which encodes for a lysophosphatidic acid (LPA) receptor. Reintroduction of EDG2 into cells that express Nm23-H1 overcame the metastasis suppressive ability of Nm23-H1 in both in vivo pulmonary colonization and spontaneous metastasis assays. In addition, isotope capture affinity tag (ICAT) proteomic analysis was performed to identify differentially expressed proteins not accounted for by microarray analysis. ICAT identified several differentially regulated proteins, including GEMIN5, a protein involved in differential mRNA splicing. The contribution of alternative mRNA splicing to cancer and cancer metastasis is poorly defined. It is possible that Nm23-H1, through the regulation of RNA processing proteins, may play a role in proteome stability.

Clinical-translational approaches to the Nm23-H1 metastasis suppressor

Nm23-H1 significantly reduces metastasis without effects on primary tumor size and was the first discovered metastasis suppressor gene. At least three mechanisms are thought to contribute to the metastasis-suppressive effect of Nm23-H1: (a) its histidine kinase activity toward ATP-citrate lyase, aldolase C, and the kinase suppressor of ras, with the last inactivating mitogen-activated protein kinase signaling; (b) binding proteins that titer out "free" Nm23-H1 and inhibit its ability to suppress metastasis; and (c) altered gene expression downstream of Nm23-H1, particularly an inverse association with the lysophosphatidic acid receptor endothelial differentiation gene-28 (EDG2). Most metastasis suppressor genes, including Nm23-H1, affect metastatic colonization, which is the outgrowth of tumor cells in distant locations; therefore, they are of high translational interest. A phase II trial is ongoing to test the hypothesis that a compound, high-dose medroxyprogesterone acetate (MPA), used as an unconventional gluocorticoid, will stimulate breast cancer cells to reexpress Nm23-H1 and limit subsequent metastatic colonization.

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.

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.

Translational approaches using metastasis suppressor genes

Cancer metastasis is a significant contributor to breast cancer patient morbidity and mortality. In order to develop new anti-metastatic therapies, we need to understand the biological and biochemical mechanisms of metastasis. Toward these efforts, we and others have studied metastasis suppressor genes, which halt metastasis in vivo without affecting primary tumor growth. The first metastasis suppressor gene identified was nm23, also known as NDP kinase. Nm23 represents the most widely validated metastasis suppressor gene, based on transfection and knock-out mouse strategies. The biochemical mechanism of metastasis suppression via Nm23 is unknown and likely complex. Two potential mechanisms include binding proteins and a histidine kinase activity. Elevation of Nm23 expression in micrometastatic tumor cells may constitute a translational strategy for the limitation of metastatic colonization in high risk cancer patients. To date, medroxyprogesterone acetate (MPA) has been identified as a candidate compound for clinical testing.

Understanding the molecular basis of the interaction between NDPK-A and AMPK alpha 1

Nucleoside diphosphate kinase (NDPK) (nm23/awd) belongs to a multifunctional family of highly conserved proteins (approximately 16 to 20 kDa) including two well-characterized isoforms (NDPK-A and -B). NDPK catalyzes the conversion of nucleoside diphosphates to nucleoside triphosphates, regulates a diverse array of cellular events, and can act as a protein histidine kinase. AMP-activated protein kinase (AMPK) is a heterotrimeric protein complex that responds to the cellular energy status by switching off ATP-consuming pathways and switching on ATP-generating pathways when ATP is limiting. AMPK was first discovered as an activity that inhibited preparations of acetyl coenzyme A carboxylase 1 (ACC1), a regulator of cellular fatty acid synthesis. We recently reported that NDPK-A (but not NDPK-B) selectively regulates the alpha1 isoform of AMPK independently of the AMP concentration such that the manipulation of NDPK-A nucleotide trans-phosphorylation activity to generate ATP enhanced the activity of AMPK. This regulation occurred irrespective of the surrounding ATP concentration, suggesting that "substrate channeling" was occurring with the shielding of NDPK-generated ATP from the surrounding medium. We speculated that AMPK alpha1 phosphorylated NDPK-A during their interaction, and here, we identify two residues on NDPK-A targeted by AMPK alpha1 in vivo. We find that NDPK-A S122 and S144 are phosphorylated by AMPK alpha1 and that the phosphorylation status of S122, but not S144, determines whether substrate channeling can occur. We report the cellular effects of the S122 mutation on ACC1 phosphorylation and demonstrate that the presence of E124 (absent in NDPK-B) is necessary and sufficient to permit both AMPK alpha1 binding and substrate channeling.

Regulation of metastasis-suppressive gene Nm23-H1 on glycosyl-transferases involved in the synthesis of sialyl Lewis antigens

By using reverse transcriptase-polymerase chain reaction (RT-PCR), the mRNA expressions of three families of glycosyltransferases involved in the synthesis of sialyl Lewis antigens were determined in H7721 human hepatocarcinoma cell line before and after the transfection of metastasis-suppressive gene nm23-H1. These glycosyltransferases included alpha1,3fucosyltransferase (alpha1,3FucT)-III, -IV, -VI, -VII, and -IX, alpha2,3-sialyltransferase (ST3Gal)-I, -II, -III, and -IV as well as O-glycan core 2 beta1,6 N-acetylglucosaminyltransferase (C2GnT)-I and -II. In mock cells transfected with the vector, the expression-order of alpha1,3FucTs was IV>VI>III>VII>IX, that of ST3Gals was IV>I>II>III, and that of C2GnT was I>II. Nm23-H1 downregulated the mRNA expressions of all five subtypes of alpha1,3FucT and -I, -III, -IV subtypes of ST3Gal, but not ST3Gal-II and C2GnT-I, II. On the other hand, the expressions of cell surface sialyl Lewis X (SLe(x)) and alpha2,3 sialyl residues were decreased on nm23-H1 transfected cells as detected with monoclonal antibody of SLe(x) and enzyme-labeled lectins, respectively. Since SLe(x) was reported to be a metastasis-associated glycan structure, the reduced expressions of SLe(x) and some enzymes related to its synthesis may be one of the mechanisms to explain the metastasis-suppressive effect of nm23-H1.

Increased lung metastasis in transgenic NM23-Null/SV40 mice with hepatocellular carcinoma

BACKGROUND

The metastasis-suppressing role of the NM23 gene in the metastatic spread of solid tumors is still debated. We examined the role of NM23 in tumor development and metastatic dissemination by using transgenic mice that lack mouse NM23 (NM23-M1) in two mouse models of hepatocellular carcinoma (HCC) that recapitulate all steps of tumor progression.

METHODS

We induced HCC in mice that contained (NM23-M1(+/+)) or lacked (NM23-M1(-/-)) NM23-M1 by diethylnitrosamine injection or by a crossing scheme that transferred a transgene that leads to liver expression of simian virus 40 large T antigen (ASV mice). We used microscopic examination and immunohistochemistry to analyze tumor progression. Expression of Nm23 protein isoforms (Nm23-M1 and Nm23-M2) and several tumor markers was analyzed in the primary tumor and in metastases by Western blotting. The statistical significance of differences in the incidence of Nm23-M2 overexpression in null mice relative to that in wild-type mice was tested by a one-sided Fisher's exact test. The statistical significance of differences in the incidence of metastases was examined using one-sided chi-square tests. All other statistical tests were two-sided.

RESULTS

In both models, Nm23-M1 and/or Nm23-M2 were overexpressed in the primary liver tumors compared with nontumor liver tissue; however, the lack of the NM23-M1 gene had no effect on primary tumor formation in either model. ASV mice developed pulmonary metastases that were positive for the Hep-Par 1 antibody, which recognizes a specific hepatocyte antigen, whereas the few pulmonary nodules that developed in diethylnitrosamine-injected mice were negative for this antigen. Statistically significantly more ASV/NM23-M1(-/-) mice than ASV/NM23-M1(+/+) mice developed lung metastases (69.2% versus 37.5%; difference = 31.7%, 95% confidence interval = 13.1% to 50.3%; P<.001). In ASV/NM23-M1(+/+) mice, immunohistochemical staining for Nm23-M1 was highly heterogeneous among the primary liver tumors, but weak or negative among lung metastases.

CONCLUSIONS

The lack of NM23-M1 expression promotes metastasis in the SV40 animal model of liver carcinogenesis.

Medroxyprogesterone acetate elevation of Nm23-H1 metastasis suppressor expression in hormone receptor-negative breast cancer

BACKGROUND

Reestablishment of metastasis suppressor gene expression may constitute a therapeutic strategy for high-risk breast cancer patients. We previously showed that medroxyprogesterone acetate (MPA), a progestin that has been tested as treatment for advanced breast cancer, elevates expression of the Nm23-H1 metastasis suppressor gene in hormone receptor-negative metastatic human breast carcinoma cell lines in vitro via a glucocorticoid receptor-based mechanism. Here, we tested whether MPA treatment inhibits metastatic colonization of a hormone receptor-negative breast cancer cell line in vivo.

METHODS

We tested the soft-agar colony-forming efficiency of untransfected MDA-MB-231T human breast carcinoma cells and MDA-MB-231T cells transfected with antisense Nm23-H1 in the presence and absence of MPA. Pharmacokinetic studies were used to establish dose and injection schedules that led to MPA serum levels in mice similar to those achievable in humans. For in vivo studies, nude mice were injected intravenously with MDA-MB-231T cells. After 4 weeks, mice were randomized to control or MPA arms. Endpoints included incidence, number, and size of gross pulmonary metastases; Nm23-H1 protein expression in gross metastases; and side effects. All statistical tests were two-sided.

RESULTS

MPA reduced colony formation of MDA-MB-231T cells by 40%-50% but had no effect on colony formation of Nm23-H1 antisense transfectants. Metastases developed in 100% (95% confidence interval [CI] = 78% to 100% and 77% to 100%, respectively) of control mice injected with MDA-MB-231T cells. In two independent experiments, only 73% (95% CI = 45% to 92%) and 64% (95% CI = 35% to 87%) of mice injected with 2 mg of MPA developed metastases. Mice injected with 2 mg of MPA showed reductions in the mean numbers, per mouse, of all metastases and of large (>3 mm) metastases (P = .04 and .013, respectively). Nm23-H1 was expressed at high levels in 43% of pulmonary metastases in MPA-treated mice but only 13% of metastases in untreated mice. Mice receiving at least 1-mg doses of MPA gained more weight than control-treated mice but exhibited no bone density alterations or abnormal mammary fat pad histology.

CONCLUSION

Our preclinical results show that MPA appears to elevate Nm23-H1 metastasis suppressor gene expression, thereby reducing metastatic colonization. The data suggest a new use for an old agent in a molecularly defined subset of breast cancer patients.

Nm23-H1 metastasis suppressor expression level influences the binding properties, stability, and function of the kinase suppressor of Ras1 (KSR1) Erk scaffold in breast carcinoma cells

Metastatic disease is a significant contributor to cancer patient mortality. We previously reported that the Kinase Suppressor of Ras1 (KSR1) scaffold protein for the Erk mitogen-activated protein kinase pathway coimmunoprecipitated the metastasis suppressor protein Nm23-H1. We now hypothesize that altered expression levels of Nm23-H1 influence the binding properties, stability, and function of the KSR1 scaffold. Increased coimmunoprecipitation of Hsp90 with KSR1 was observed in either stable or transient transfectants of nm23-H1 in MDA-MB-435 human breast carcinoma cells. Similar trends were also observed in the cytoplasmic and nuclear fractions of cells. Cells expressing high levels of Nm23-H1 exhibited increased KSR1 degradation in the presence of either cycloheximide or an Hsp90-directed drug currently in clinical trial, 17-allylamino-17-demethoxygeldanamycin (17-AAG). In agreement with KSR1 degradation data, high-Nm23-H1-expression cells were preferentially inhibited in anchorage-independent colonization assays by 17-AAG. KSR1 scaffold binding patterns are dynamic in both the cytoplasmic and nuclear compartments, modulated by metastasis suppressor expression. Metastasis suppressor expression levels can impact traditional signaling pathways, such as the Erk pathway, resulting in altered tumor cell sensitivity to cancer therapeutics.

Co-downregulation of PTEN, KAI-1, and nm23-H1 tumor/metastasis suppressor proteins in non-small cell lung cancer

The multistep process of carcinogenesis implies the accumulation of multiple molecular defects. Alteration of tumor suppressor and metastasis suppressor genes are the important steps. Increasing experimental evidence indicates that decreased expression of tumor-metastasis/suppressor genes and gene products are involved in the progression of a variety of human malignancies. In the present study, we have extended this analysis to non-small cell lung carcinomas (NSCLC). The expression and prognostic significance of the tumor suppressor gene PTEN and metastasis suppressor genes nm23-H1 and KAI-1 was evaluated in NSCLCs. Immunohistochemical staining was performed on formalin-fixed, paraffin-embedded tissues from 53 bronchogenic adenocarcinomas and 51 squamous cell carcinomas using monoclonal antibodies against PTEN, nm23H-1, and KAI-1 proteins. Immunohistochemical results were correlated with tumor stage, grade, lymph nodes positivity, metastasis, and patient survival. Significant co-expression of PTEN, nm23-H1 and KAI-1 was observed in NSCLC (P<.001 to .002). The immunohistochemical expression of these proteins was significantly higher in stages 1 and 2 compared with stages 3 and 4 (P=.04 for PTEN and KAI-1, P=.039 for nm23-H1). When all stages were considered together, loss of immunoreactivity for PTEN, nm23-H1 and KAI-1 was found in advanced NCSCLs (P=.015 for PTEN, P=.001 for KAI-1, P=.004 for nm23-H1), which is suggestive of co-downregulation of these proteins in the process of tumor progression. On multivariate analysis, negative staining for PTEN (P=.014), KAI-1 (P=.034), and nm23-H1 (a trend toward association for nm23-H1 reached near significance P=.08) correlated with disease-related death. Positive lymph node status was associated with negative immunostaining for PTEN (P=.007) but no correlation was observed for nm23-H1 and KAI-1. Loss of expression was linked to distant metastasis (P=.006 for PTEN, P=.002 for nm23H1, P=.001 for KAI-1). On multivariate analysis, co-downregulation of PTEN (P=.009), KAI-1 (P=.02), and nm23-H1 (P=.011) independently predicted shortened survival in NSCLC. Although NSCLC exhibits strong co-expression of PTEN, nm23-H1 and KAI-1, there is a loss of these proteins in high-stage tumors. Co-downregulation of PTEN, KAI-1, and nm23-H1 significantly correlates with distant metastasis and predicts shortened survival. Our study supports a role of these tumor suppressor and metastasis suppressor genes in the evolution and progression of NSCLC.

Metastasis suppressor genes: basic biology and potential clinical use

Metastatic disease remains a significant contributor to morbidity and mortality in patients with breast cancer. An improved molecular and biochemical understanding of the metastatic process is expected to fuel the development of new therapeutic approaches. The suppression of tumor metastasis, despite tumor cell expression of oncogenes and metastasis-promoting events, has become a diverse and fruitful field of investigation. Although many genetic events promote metastasis, several genes show relatively reduced expression levels in metastatic tumor cells in mouse model systems and in aggressive human tumors. Re-expression of a metastasis-suppressor gene in a metastatic tumor cell line results in a significant reduction in metastatic behavior in vivo with no effect on tumorigenicity. The known metastasis-suppressor gene products nm23, KAI1, mitogen-activated protein kinase kinase 4, breast cancer metastasis suppressor-1, KiSS1, RHOGDI2, CRSP3, and vitamin D3-upregulated protein/thioredoxin interacting protein exhibit unexpected biochemical functions that have shed new light on signaling events that are important in metastasis. Most metastasis suppressors function at the translationally important stage of outgrowth of micrometastatic tumor cells at a distant site. We hypothesize that elevation of metastasis suppressor gene expression in micrometastatic tumor cells in the adjuvant high-risk population of patients with breast cancer will halt metastatic colonization and have a clinical benefit. DNA methylation inhibitors have shown limited promise in increasing metastasis-suppressor gene expression, and ligands of the nuclear hormone receptor family are currently under investigation in vitro and in vivo. Clinical testing of agents that increase metastasis-suppressor gene expression is expected to require tailored trial designs.

Inhibition of signal transduction by the nm23 metastasis suppressor: possible mechanisms

The first metastasis suppressor gene identified was nm23. Transfection of nm23 into metastatic cell lines resulted in the inhibition of metastasis, but not primary tumor size in vivo. Using in vitro assays, nm23 overexpression resulted in reduced anchorage-independent colonization in response to TGF-beta, reduced invasion and motility in response to multiple factors, and increased differentiation. We hypothesize that the mechanism of action of Nm23 in metastasis suppression involves diminished signal transduction downstream of a particular receptor. Candidate biochemical mechanisms are identified and discussed herein.

Histidine kinases and histidine phosphorylated proteins in mammalian cell biology, signal transduction and cancer

Intensive investigation of protein tyrosine, serine and threonine phosphorylation has lead to advances in signal transduction research and cancer treatment. This feature summarizes research on mammalian proteins exhibiting histidine phosphorylation. Histidine kinases are well known in prokaryotic and lower eukaryotic systems where they form the 'two-component' signal transduction system. The relative invisibility of histidine phosphorylation in mammalian cells may result from technical obstacles such as its acid lability, which precludes detection in electrophoretic systems, amino acid sequencing, etc. Emerging data have identified mammalian histidine kinases for the kinase suppressor of ras, a scaffold molecule for the Map kinase pathway, as well as histone H4, aldolase C and the beta-subunit of heterotrimeric G proteins. Additional mammalian proteins of interest to signal transduction and cancer research exhibit histidine phosphorylation, including P-selectin, annexin I and the 20S proteasome. Other candidate histidine phosphorylated proteins are identified. These data suggest the existence of another series of phosphorylation patterns in signal transduction.

Nucleoside diphosphate kinases in mammalian signal transduction systems: recent development and perspective

The role of nucleoside diphosphate (NDP) kinase with special reference to mammalian signal transduction systems was described. The interaction between NDP kinases and G proteins was reevaluated in view of their protein structural information and its significance was extended further on the basis of recent findings obtained with small molecular weight G proteins such as Rad, menin, and Rac. Meanwhile, observations suggesting involvement of NDP kinases in the regulation of cell growth and differentiation led to the realization that NDP kinases may play a crucial role in receptor tyrosine kinase signal transduction systems. In fact, a number of experimental results, particularly obtained with PC12 cells, implicate that NDP kinases appear to regulate differentiation marker proteins and cell-cycle-associated proteins cooperatively. Consequently, we propose a hypothesis that NDP kinases might act like a molecular switch to determine the cell fate toward proliferation or differentiation in response to environmental signals.

Molecular evolution of nucleoside diphosphate kinase genes: conserved core structures and multiple-layered regulatory regions

Genomic data regarding the nucleoside diphosphate (NDP) kinase genes have been accumulated from diverged phyla. Comparison of their regulatory sequences have shed light on the multiple facets of gene regulation systems. Phylogenetic studies, including CpG island and intron-mapping, and homologous sequence comparison, have suggested that the regions of the major mammalian genes, the ortholog (rat alpha or nm23-H2) and its paralog (rat beta or nm23-H1), have been constructed by a stepwise gain and loss of alien genes resulting in "multiple-layered" regulatory systems. They contain representative cis-elements for the constitutive, stage/lineage-specific, and early response expression. These elements' binding capacities to nuclear proteins were confirmed by electrophoretic mobility shift assay. Further, these regulatory systems generate heterogeneous mRNA at the 5' untranslated region, which influences their own translation efficiencies. In terms of this process, the transcription system would control another layer of gene expression: posttranscriptional (translational) regulation.

Basic and translational advances in cancer metastasis: Nm23

Cancer metastasis is a significant contributor to breast cancer patient morbidity and mortality. To develop new anti-metastatic therapies, we need to understand the biological and biochemical mechanisms of metastasis. Toward these efforts, we and others have studied metastasis suppressor genes, which halt metastasis in vivo without affecting primary tumor growth. The first metastasis suppressor gene confirmed was nm23, also known as NDP kinase. Using in vitro assays, nm23 overexpression resulted in reduced anchorage-independent colonization in response to TGF-beta, reduced invasion and motility in response to multiple factors, and increased differentiation. We hypothesize that the mechanism of action of Nm23 in metastasis suppression involves diminished signal transduction, downstream of a particular receptor. We hypothesize that a histidine protein kinase activity of Nm23 underlies its suppression of metastasis, and identify candidate substrates. This review also discusses therapeutic options on the basis of reexpression of metastasis suppressors.

Metastasis suppressors alter the signal transduction of cancer cells

Tumour metastasis is a significant contributor to death in cancer patients. Eight metastasis-suppressor genes that reduce the metastatic propensity of a cancer cell line in vivo without affecting its tumorigenicity have been identified. These affect important signal-transduction pathways, including mitogen-activated protein kinases, RHO, RAC and G-protein-coupled and tyrosine-kinase receptors. So how might we use this knowledge to improve the treatment of patients with cancer?

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.

Nm23-H1 metastasis suppressor phosphorylation of kinase suppressor of Ras via a histidine protein kinase pathway

The metastasis-suppressive activity of Nm23-H1 was previously correlated with its in vitro histidine protein kinase activity, but physiological substrates have not been identified. We hypothesized that proteins that interact with histidine kinases throughout evolution may represent partners for Nm23-H1 and focused on the interaction of Arabidopsis "two-component" histidine kinase ERS with CTR1. A mammalian homolog of CTR1 was previously reported to be c-Raf; we now report that CTR1 also exhibits homology to the kinase suppressor of Ras (KSR), a scaffold protein for the mitogen-activated protein kinase (MAPK) cascade. Nm23-H1 co-immunoprecipitated KSR from lysates of transiently transfected 293T cells and at endogenous protein expression levels in MDA-MB-435 breast carcinoma cells. Autophosphorylated recombinant Nm23-H1 phosphorylated KSR in vitro. Phosphoamino acid analysis identified serine as the major target, and two peaks of Nm23-H1 phosphorylation were identified upon high performance liquid chromatography analysis of KSR tryptic peptides. Using site-directed mutagenesis, we found that Nm23-H1 phosphorylated KSR serine 392, a 14-3-3-binding site, as well as serine 434 when serine 392 was mutated. Phosphorylated MAPK but not total MAPK levels were reduced in an nm23-H1 transfectant of MDA-MB-435 cells. The data identify a complex in vitro histidine-to-serine protein kinase pathway, which may contribute to signal transduction and metastasis.

MMTV-associated transcription factor binding sites increase nm23-H1 metastasis suppressor gene expression in human breast carcinoma cell lines

We hypothesize that elevation of nm23-HI metastasis suppressor gene expression in micrometastatic tumor cells may reduce their subsequent colonization and invasion, and induce differentiation, with a clinical benefit. This report presents the first analysis of the nm23-HI promoter to identify sites which can increase its transcription. Deletion mapping of a 2.1 kb nm23-H1 promoter fragment tethered to a reporter gene identified three regions involved in its differential expression levels among a panel of human breast carcinoma cell lines: a 195 bp NheI-XbaI fragment responsible for basal expression levels, a 248 bp AvrII-Nhel fragment which contributed to the elevated nm23-H1 expression observed in the high expressing cell lines, and a 544 bp AvrII fragment containing an inhibitory element. Examination of the 248 bp AvrII-NheI fragment revealed the unexpected presence of three transcription factor binding sites (MAF/Ets, CTF/NF1 half site and ACAAAG enhancer) previously identified in the MMTV-LTR, and in WAP and milk gene promoters, proposed to mediate mammary-specific gene expression. Mutation of the three sites, individually or together, resulted in two-fold reductions in reporter gene expression. As controls, the same panel of mutations caused a different pattern of reporter gene expression in a non-mammary cell line, and mutation of another nearby site was without effect on nm23-HI. Our data identify a complex regulatory pattern for nm23-H1 transcription, and suggest that a mammary-specific cassette of transcription factors contribute to its elevated expression

Genome-wide expression changes induced by HTLV-1 Tax: evidence for MLK-3 mixed lineage kinase involvement in Tax-mediated NF-kappaB activation

The Tax protein of human T-lymphotropic virus type 1 (HTLV-1), an oncoprotein that transactivates viral and cellular genes, plays a key role in HTLV-1 replication and pathogenesis. We used cDNA microarrays to examine Tax-mediated transcriptional changes in the human Jurkat T-cell lines JPX-9 and JPX-M which express Tax and Tax-mutant protein, respectively, under the control of an inducible promoter. Approximately 300 of the over 2000 genes examined were differentially expressed in the presence of Tax. These genes were grouped according to their function and are discussed in the context of existing findings in the literature. There was strong agreement between our results and genes previously reported as being Tax-responsive. Genes that were differentially expressed in the presence of Tax included those related to apoptosis, the cell cycle and DNA repair, signaling factors, immune modulators, cytokines and growth factors, and adhesion molecules. Functionally, we provide evidence that one of these genes, the mixed-lineage kinase MLK-3, is involved in Tax-mediated NF-kappa-B signaling. Our current results provide additional insights into Tax-mediated signaling.

Characterization and partial sequencing of species-specific sarcoplasmic polypeptides from commercial hake species by mass spectrometry following two-dimensional electrophoresis

The Merluccidae family comprises marine species, some of them of high commercial value and others less appreciated, whose commercialization in Europe under the generic name of "hake" is highly remarkable. The potential of proteomics was employed in this study with the aim of achieving the differential characterization of five different hake species: Merluccius merluccius (European hake), M. australis (Southern hake), M. hubbsi (Argentinian hake), M. gayi (Chilean hake), and M. capensis (Cape hake), some of them very closely related. Species-specific polypeptides were observed for the five hake species studied in isoelectric focusing (IEF) and/or two-dimensional electrophoresis (2-DE) high-resolution gels. The peptide mass maps of two polypeptide groups, previously selected by 2-DE analysis as potentially species-specific, were obtained by "in-gel" tryptic digestion, followed by matrix assisted laser desorption/ ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Analysis of group A polypeptides (with pI in the range of 5.0-5.5 and molecular mass of 17 kDa), allowed the differential classification of the hake species into two groups: the East Atlantic coast group and the West Atlantic coast group. Moreover, the peptide mass-maps from the heat-resistant parvalbumin fraction (pI below 4.5; molecular mass <12 kDa) allowed the detection of a peptide characteristic of M. australis not present in the other four hake species tested. A specific 17 kDa protein from M. merluccius was also partially sequenced by nanospray-ion trap-tandem MS, revealing a high homology with rat nucleoside diphosphate kinase A (NDKA). This work opens the way to the application of proteomics to the differential characterization of commercial hake species at the molecular level.

Nucleoside diphosphate kinase, a source of GTP, is required for dynamin-dependent synaptic vesicle recycling

Nucleoside diphosphate kinase (NDK), an enzyme encoded by the Drosophila abnormal wing discs (awd) or human nm23 tumor suppressor genes, generates nucleoside triphosphates from respective diphosphates. We demonstrate that NDK regulates synaptic vesicle internalization at the stage where function of the dynamin GTPase is required. awd mutations lower the temperature at which behavioral paralysis, synaptic failure, and blocked membrane internalization occur at dynamin-deficient, shi(ts), mutant nerve terminals. Hypomorphic awd alleles display shi(ts)-like defects. NDK is present at synapses and its enzymatic activity is essential for normal presynaptic function. We suggest a model in which dynamin activity in nerve terminals is highly dependent on NDK-mediated supply of GTP. This connection between NDK and membrane internalization further strengthens an emerging hypothesis that endocytosis, probably of activated growth factor receptors, is an important tumor suppressor activity in vivo.

Identification of the tumor metastasis suppressor Nm23-H1/Nm23-R1 as a constituent of the centrosome

Processes like cell proliferation, differentiation, and tumor metastasis require a flexible adaptation of cell shape and cell plasticity. A regulator of cell structure and shape is the centrosome and its associated microtubules. Recently, oncogenes like p53, pRB, and the tumor suppressor BRCA1 have been characterized as members of the centrosome. In this communication, we identified rat Nm23-R1/NDPKbeta, a homologue of the human tumor metastasis suppressor Nm23-H1 and a regulator of cell proliferation and differentiation, as a component of the centrosomal complex. We used confocal laser scanning microscopy on different cell types and biochemical analysis of purified centrosomes to demonstrate that Nm23-R1 is located in the centrosome of dividing and nondividing cells. We also showed that the centrosomal enzyme is catalytically active and able to transfer the gamma-phosphate from a nucleoside triphosphate to a nucleoside diphosphate. In addition, Nm23-R1 coimmunoprecipitated with gamma-tubulin, a core centrosomal protein essential for microtubule nucleation. In addition, human Nm23-R1/-H1 was also shown to be present in the centrosome of different human and rat cell types, demonstrating that the presence of Nm23-H1 homologues in the latter organelle is a general event.

Phosphorylation of geranyl and farnesyl pyrophosphates by Nm23 proteins/nucleoside diphosphate kinases

The biochemical mechanism(s) by which Nm23 proteins/nucleoside diphosphate kinases suppress tumor metastasis, inhibit cell motility, and affect cellular differentiation are not known. Here we report that Nm23 proteins can phosphorylate geranyl and farnesyl pyrophosphates to give triphosphates. Wild type Nm23-H1 had higher geranyl and farnesyl pyrophosphate kinase activities than did mutants of Nm23-H1 that do not inhibit cell motility. The phosphorylation of farnesyl pyrophosphate appears to occur in vivo as cells with an elevated level of Nm23-H1 contained more farnesyl triphosphate than did control cells. To our knowledge, this is the first report that farnesyl triphosphate exists in cells. The phosphorylation of farnesyl pyrophosphate by Nm23 proteins could alter isoprenoid metabolism, and cells with an elevated level of Nm23 proteins were found to contain more farnesylated 46- and 24-kDa proteins than did control cells. The phosphorylation of geranyl and farnesyl pyrophosphates by Nm23 proteins provides a novel mechanism by which these proteins might exert their biological effects.

Down-regulation of N-acetylglucosaminyltransferase V by tumorigenesis- or metastasis-suppressor gene and its relation to metastatic potential of human hepatocarcinoma cells

The effects of transfection of the metastasis suppressor gene nm23-H1 and cell-cycle related tumor-suppressor gene p16 on the activity of N-acetylglucosaminyltransferase V (GnT-V) and their relations to cancer metastatic potential were investigated. After transfection of nm23-H1 into 7721 human hepatocarcinoma cells and A549 human lung cancer cells, the activities of GnT-V were decreased by 28%-42% in the cells. In contrast, when p16 was transfected into these two cell lines, the decrease of GnT-V activity was only observed in A549 cells. This was probably to be due to the obvious expression of p16 gene in parental 7721 cells and the deletion of p16 in A549 cells. The decrease of GnT-V mRNA was only observed in nm23-H1-transfected cells, but not in p16-transfected A549 cells, suggesting that these two genes regulated GnT-V via different mechanisms. Horseradish peroxidase (HRP)-lectin staining showed that the 7721 cells transfected with nm23-H1 or the A549 cells transfected with p16 displayed a decreased intensity with HRP-leucoagglutinating phytohemagglutinin and increased intensity with HRP-concanavalin A, indicating the decline of beta1,6 N-acetylglucosamine branching structure on the asparagine-linked glycans of cell-surface and intracellular glycoproteins. The nm23-H1 transfected 7721 cells also displayed some changes in metastasis-related phenotypes, including the increase in cell adhesion to fibronectin (Fn), the decline in cell adhesion to laminin (Ln), and the decreased cell migration and invasion through matrigel. Transfection of antisense GnT-V cDNA into 7721 cells resulted in a decrease of GnT-V activity, an increase of cell adhesion to Fn or Ln, and a decrease in cell migration and invasion through matrigel. These phenotypes bore similarity to those of the 7721 cells transfected with nm23-H1. Our findings indicate that the down-regulation of GnT-V by nm23-H1 contributes to the alterations in metastasis-related phenotypes, and is an important molecular mechanism of metastasis suppression mediated by nm23-H1.

Negative regulation of the antimetastatic gene Nm23-H1 by thyroid hormone receptors

Metastasis of various malignant cells is inversely related to the abundance of the Nm23-H1 protein. The possible role of thyroid hormones in tumor metastasis has now been investigated by examining the effect of T3 on the expression of the Nm23-H1 gene. Human hepatoma HepG2 cells, in which endogenous thyroid hormone receptor subtype alpha1 (TRalpha1) is expressed at a low level, were stably transfected, either with expression plasmids encoding wild-type TRalpha1 or a dominant negative mutant of TRalpha1, or with the empty vector (yielding HepG2-Wt, HepG2-Mt, and HepG2-Neo cells, respectively). Immunoblot analysis revealed that exposure of HepG2-Wt and HepG2-Neo cells, but not HepG2-Mt cells, to T3-induced time-dependent decreases in the abundance of Nm23-H1 messenger RNA and protein, with the extent of these effects correlating with the level of expression of TRalpha1. An in vitro assay also revealed that T3 induced a marked increase in the invasive activity of HepG2-Wt cells; it induced a smaller increase in that of HepG2-Neo cells but had no effect on that of HepG2-Mt cells. Finally, the promoter region of Nm23-H1 spanning nucleotides -471 to -437 (relative to the transcriptional initiation site) inhibited the expression of a downstream reporter gene, in a T3-dependent manner, in COS-1 cells also transfected with an expression plasmid encoding TRalpha1 or TRbeta1. The DNA binding domain of TRbeta1 was required for this inhibitory effect. These results indicate that T3, acting through TRs, inhibits transcription of Nm23-H1, and that this effect is mediated by a negative regulatory element in the promoter region of the gene. Thus, it is possible that T3 promotes tumor metastasis by inducing down-regulation of Nm23-H1 expression.

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.

Regulation of cellular functions by nucleoside diphosphate kinases in mammals

The role of nucleoside diphosphate (NDP) kinases in cell growth, differentiation, and tumor metastasis in relation to signal transduction was investigated. The essential role of NDP kinase in cell growth was validated by coupling between reduced NDP kinase levels, induced by antisense oligonucleotides, and the suppression of proliferative activity of a cultured cell line. In addition, because NDP kinase levels are often enhanced with development and differentiation, as has been demonstrated in postmitotic cells and tissues, such as the heart and brain, we further examined this possibility using the bone tissue (osteoblasts) and a cultured cell line PC12D. The enhanced NDP kinase accumulation was demonstrated in the matured osteoblasts in vivo and in vitro by immunohistochemistry. In PC12D cells, neurite outgrowth took place in NDP kinase beta-transfected clones without differentiation inducers, which was accompanied by prolongation of doubling time. Neurite outgrowth, triggered by nerve growth factor and a cyclic AMP analog, was down-regulated upon forced expression of inactive mutant NDP kinase by virtue of a dominant negative effect. NDP kinase alpha-transfected rat mammary adenocarcinoma cells (MTLn3) and nm23-H2-transfected human oral squamous cell carcinoma cells (LMF4) manifested reduced metastatic potential and were associated with an altered sensitivity to environmental factors, such as motility and growth factors. NDP kinase alpha, compared to NDP kinase beta, was involved in a wide variety of the cellular phenomena examined. Taken together, NDP kinase isoforms appear to elicit both their own respective and common effects. They may have an ability to lead cells to both proliferative and differentiated states by modulating responsiveness to environmental factors, but their fate seems to depend on their surrounding milieu.

Wild-type NM23-H1, but not its S120 mutants, suppresses desensitization of muscarinic potassium current

NM23 (NDP kinase) modulates the gating of muscarinic K+ channels by agonists through a mechanism distinct from GTP regeneration. To better define the function of NM23 in this pathway and to identify sites in NM23 that are important for its role in muscarinic K+ channel function, we utilized MDA-MB-435 human breast carcinoma cells that express low levels of NM23-H1. M2 muscarinic receptors and GIRK1/GIRK4 channel subunits were co-expressed in cells stably transfected with vector only (control), wild-type NM23-H1, or several NM23-H1 mutants. Lysates from all cell lines tested exhibit comparable nucleoside diphosphate (NDP) kinase activity. Whole cell patch clamp recordings revealed a substantial reduction of the acute desensitization of muscarinic K+ currents in cells overexpressing NM23-H1. The mutants NM23-H1P96S and NM23-H1S44A resembled wild-type NM23-H1 in their ability to reduce desensitization. In contrast, mutants NM23-H1S120G and NM23-H1S120A completely abolished the effect of NM23-H1 on desensitization of muscarinic K+ currents. Furthermore, NM23-H1S120G potentiated acute desensitization, indicating that this mutant retains the ability to interact with the muscarinic pathway, but has properties antithetical to those of the wild-type protein. We conclude that NM23 acts as a suppressor of the processes leading to the desensitization of muscarinic K+ currents, and that Ser-120 is essential for its actions.

Overexpression of nucleoside diphosphate kinases induces neurite outgrowth and their substitution to inactive forms leads to suppression of nerve growth factor- and dibutyryl cyclic AMP-induced effects in PC12D cells

Whether nucleoside diphosphate kinase (NDPK) is involved in neuronal differentiation was investigated with special reference to its enzyme activity. Neurite outgrowth of PC12D cells induced by nerve growth factor or a cyclic AMP analog was suppressed to some extent when inactive NDPKs (the active site histidine 118 was replaced with alanine), not active forms, were transiently overexpressed. This suppression was more definite in their stably expressed clones. NDPKbeta-transfected clones and, to a lesser extent, NDPKalpha-transfected clones, but not inactive NDPK-transfected clones, extended neurites without differentiation inducers. These results imply that NDPKs may play a role by exerting their enzyme activity during differentiation of PC12 cells.

Differentiation inhibitory factor Nm23 as a prognostic factor for acute myeloid leukemia

The differentiation inhibitory factor nm23 inhibits the differentiation of murine and human myeloid leukemia cells. The inhibition of differentiation may be associated with the aggressive behavior of leukemia. To clarify the role of nm23 in human myeloid leukemia, we investigated the relative levels of nm23-H1, nm23-H2 and c-myc transcripts in bone marrow and blood samples from 110 patients with acute myeloid leukemia (AML) using the reverse transcriptase polymerase chain reaction. The expression levels of nm23-H1 and nm23-H2 in these AML samples were significantly higher than in normal blood cells, and a higher level of nm23-H1 expression was correlated with poor prognosis for AML patients. Analysis of the correlation between nm23 expression and clinical parameters demonstrated that increased nm23-H1 mRNA levels were associated with resistance to initial chemotherapy and reduced overall survival. Multivariate analysis of putative prognostic factors revealed that elevated nm23-H1 mRNA levels significantly influenced the prognosis of patients with AML, particularly in AML-M5.

Nm23/PuF does not directly stimulate transcription through the CT element in vivo

Decreased levels of the nm23 gene product have been correlated with increased tumor metastatic potential in a variety of malignancies. At least a subset of the regulatory properties of Nm23 has been proposed to be due to transactivation of the human c-myc oncogene through binding to a homopyrimidine tract 140 base pairs upstream of the transcription start site (termed the CT element or the PuF site). Conventional transcription factors possess DNA binding and transactivation domains; Nm23 fusion proteins were used to address two questions. First, if provided with a well characterized DNA binding domain, does Nm23 possess a transactivation domain capable of stimulating transcription of an appropriate reporter? Second, if provided with a potent transactivation domain, is the DNA binding of Nm23 of sufficient specificity and affinity to direct the fusion protein to a CT-dependent reporter? Since reporter gene expression was not stimulated in either case, we conclude that Nm23 does not directly stimulate transcription through binding to the CT element and that its antimetastatic and other reported functions are likely due to other biochemical activities.

Two-component kinase-like activity of nm23 correlates with its motility-suppressing activity

Nm23 genes, which encode nucleoside diphosphate kinases, have been implicated in suppressing tumor metastasis. The motility of human breast carcinoma cells can be suppressed by transfection with wild-type nm23-H1, but not by transfections with two nm23-H1 mutants, nm23-H1(S12OG) and nm23-H1(P96S). Here we report that nm23-H1 can transfer a phosphate from its catalytic histidine to aspartate or glutamate residues on 43-kDa membrane proteins. One of the 43-kDa membrane proteins was not phosphorylated by either nm23-H1(P96S) or nm23-H1(S120G), and another was phosphorylated much more slowly by nm23-H1(P96S) and by nm23-H1(S120G) than by wild-type nm23-H1. Nm23-H1 also can transfer phosphate from its catalytic histidine to histidines on ATP-citrate lyase and succinic thiokinase. The rates of phosphorylation of ATP-citrate lyase by nm23-H1(S120G) and nm23-H1(P96S) were similar to that by wild-type nm23-H1. The rate of phosphorylation of succinic thiokinase by nm23-H1(S120) was similar to that by wild-type nm23-H1, and the rate of phosphorylation of succinic thiokinase by nm23-H1(P96S) was about half that by wild-type nm23-H1. Thus, the transfer of phosphate from nm23-H1 to aspartates or glutamates on other proteins appears to correlate better with the suppression of motility than does the transfer to histidines.

Suppression of human melanoma metastasis following introduction of chromosome 6 is independent of NME1 (Nm23)

Metastasis is suppressed more than 95% following microcell-mediated transfer of a single copy of neomycin-tagged human chromosome 6 (neo6) into the human melanoma cell lines C8161 and MelJuSo. Concomitant with metastasis suppression is upregulation of NME1 (Nm23-H1) mRNA and protein expression. The purposes of this study were to determine whether NME1 expression was responsible for metastasis suppression in neo6/melanoma hybrids, and whether genes on chromosome 6 regulate NME1. Using neo6/C8161 cells, transfection of CAT reporter constructs linked to the NME1 promoter failed to consistently induce CAT. Therefore, it does not appear that genes on chromosome 6 directly control transcription of NME1. Transfection and overexpression of NME1 in MelJuSo, under the control of the CMV promoter, resulted in 40-80% inhibition of lung metastasis following i.v. inoculation of 2 x 10(5) cells. Only one transfectant of C8161 subclone 9 (C8161cl.9) cells was suppressed for metastasis. Control transfections with pCMVneo or pSV2neo did not suppress metastasis in either cell line. Taken together, these data suggest that NME1 can reduce metastatic potential of some human melanoma cells; but, this inhibitory activity appears to be independent of the metastasis suppression following introduction of chromosome 6 into C8161 and MelJuSo human melanoma cell lines.

Site-directed mutation of Nm23-H1. Mutations lacking motility suppressive capacity upon transfection are deficient in histidine-dependent protein phosphotransferase pathways in vitro

We previously compared the structure and motility suppressive capacity of nm23-H1 by transfection of wild type and site-directed mutant forms into breast carcinoma cells. Wild type nm23-H1 and an nm23-H1(S44A) (serine 44 to alanine) mutant suppressed motility, whereas the nm23-H1(P96S), nm23-H1(S120G), and to a lesser extent, nm23-H1(S120A) mutant forms failed to do so. In the present study wild type and mutant recombinant Nm23-H1 proteins have been produced, purified, and assayed for phosphorylation and phosphotransfer activities. We report the first association of Nm23-H1 mutations lacking motility suppressive capacity with decreased in vitro activity in histidine-dependent protein phosphotransferase assays. Nm23-H1(P96S), a Drosophila developmental mutation homolog, exhibited normal autophosphorylation and nucleoside-diphosphate kinase (NDPK) characteristics but deficient phosphotransfer activity in three histidine protein kinase assays, using succinic thiokinase, Nm23-H2, and GST-Nm23-H1 as substrates. Nm23-H1(S120G), found in advanced human neuroblastomas, exhibited deficient activity in several histidine-dependent protein phosphotransfer reactions, including histidine autophosphorylation, downstream phosphorylation on serines, and slightly decreased histidine protein kinase activity; significant NDPK activity was observed. The Nm23-H1(S120A) mutant was deficient in only histidine-dependent serine autophosphorylation. Nm23-H1 and Nm23-H1(S44A) exhibited normal activity in all assays conducted. Based on this correlation, we hypothesize that a histidine-dependent protein phosphotransfer activity of Nm23-H1 may be responsible for its biological suppressive effects.

Multiple transcripts for rat nucleoside diphosphate kinase alpha isoform are structurally categorized into two groups that exhibit cell-specific expression and distinct translation potential

Rat nucleoside diphosphate (NDP) kinase is composed of two isoforms (alpha and beta) encoded by independent genes. The mRNAs are expressed ubiquitously; however, the level of expression is tissue-dependent and is also up- or down-regulated under certain conditions, including growth stimulation, differentiation, and tumor metastasis. To address the regulatory mechanisms of gene expression for the rat NDP kinase major isoform alpha (an nm23-H2/PuF homologue), we identified the transcription initiation sites in detail by RNase protection and 5'-rapid amplification of DNA ends and located the core promoter region by chloramphenicol acetyltransferase assay. The transcripts, initiated from an extraordinarily wide range of sites, were categorized into two groups; one transcribed from an upstream region was spliced in the untranslated region (group 1), whereas the other initiated in the downstream region was not (group 2). RNase protection demonstrated that the group 1 mRNA was the dominant form present in all tissues except heart and skeletal muscle. In situ hybridization revealed cell-specific expression of these mRNA species. Furthermore, they differed in the translational efficiency (the group 2 alpha > beta > the group 1 alpha). These findings suggest that the regulation of the NDP kinase expression at both transcriptional and posttranscriptional steps could be fundamentally governed by the selection of transcription initiation sites.