Decrease in nucleoside diphosphate kinase (NDPK/nm23) expression during hematopoietic maturation

Extracellular NME proteins: a player or a bystander?

The Nm23/NME gene family has been under intensive study since Nm23H1/NME1 was identified as the first metastasis suppressor. Inverse correlation between the expression levels of NME1/2 and prognosis has indeed been demonstrated in different tumor cohorts. Interestingly, the presence of NME proteins in the extracellular environment in normal and tumoral conditions has also been noted. In many reported cases, however, these extracellular NME proteins exhibit anti-differentiation or oncogenic functions, contradicting their canonical anti-metastatic action. This emerging field thus warrants further investigation. In this review, we summarize the current understanding of extracellular NME proteins. A role in promoting stem cell pluripotency and inducing development of central nervous system as well as a neuroprotective function of extracellular NME have been suggested. Moreover, a tumor-promoting function of extracellular NME also emerged at least in some tumor cohorts. In this complex scenario, the secretory mechanism through which NME proteins exit cells is far from being understood. Recently, some evidence obtained in the Drosophila and cancer cell line models points to the involvement of Dynamin in controlling the balance between intra- and extracellular levels of NME. Further analyses on extracellular NME will lead to a better understanding of its physiological function and in turn will allow understanding of how its deregulation contributes to carcinogenesis.

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.

Extracellular NM23 Protein as a Therapeutic Target for Hematologic Malignancies

An elevated serum level of NM23-H1 protein is a poor prognostic factor in patients with various hematologic malignancies. The extracellular NM23-H1 protein promotes the in vitro growth and survival of acute myelogenous leukemia (AML) cells and inversely inhibits the in vitro survival of normal peripheral blood monocytes in primary culture at concentrations equivalent to the levels found in the serum of AML patients. The growth and survival promoting activity to AML cells is associated with cytokine production and activation of mitogen-activated protein kinases (MAPKs) and signal transducers and activators of transcription (STAT) signaling pathways. Inhibitors specific for MAPK signaling pathways inhibit the growth/survival-promoting activity of NM23-H1. These findings indicate a novel biological action of extracellular NM23-H1 and its association with poor prognosis. These results suggest an important role of extracellular NM23-H1 in the malignant progression of leukemia and a potential therapeutic target for these malignancies.

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.

Nm23-h1 indirectly promotes the survival of acute myeloid leukemia blast cells by binding to more mature components of the leukemic clone

Nm23-H1 plays complex roles in the development of diverse cancers including breast carcinoma, high-grade lymphomas, and acute myeloid leukemia (AML). In the case of AML and lymphomas, serum Nm23-H1 protein is elevated with the highest levels correlating with poorest prognosis. A recent study identified that this association is most likely causal in AML and that Nm23-H1 acts as an AML cell survival factor. In this study, we report heterogeneity in the ability of AML samples to bind and respond to Nm23-H1, and we offer evidence that binding is essential for improved survival. Further, we show that the subset of AMLs that bind Nm23-H1 do not do so through the putative Nm23-H1 receptor MUC1*. Although rNm23-H1 promoted the survival of the most primitive blasts within responding AMLs, it was not these cells that actually bound the protein. Instead, rNm23-H1 bound to more mature CD34(lo)/CD34(-) and CD11b(+) cells, revealing an indirect survival benefit of Nm23-H1 on primitive blasts. In support of this finding, the survival of purified blast cells was enhanced by medium conditioned by more mature cells from the clone that had been stimulated by rNm23-H1. Levels of interleukin 1β (IL1β) and IL6 in rNm23-H1 conditioned medium mirrored the potency of the conditioned media to promote blast cell survival. Furthermore, Nm23-H1 expression was significantly associated with IL1β and IL6 expression in primary uncultured AML samples. These findings have implications for the role of Nm23-H1 in AML and its use as a prognostic marker. Additionally, they offer the first evidence of novel cross-talk between cell populations within the tumor clone.

Extracellular NM23 protein promotes the growth and survival of primary cultured human acute myelogenous leukemia cells

An elevated serum level of NM23-H1 protein is found in acute myelogenous leukemia (AML), and predicts a poor treatment outcome in AML patients. To investigate the potential pathological link between the elevated serum level of this protein and poor prognosis, we examined the extracellular effects of recombinant NM23-H1 protein on the in vitro growth and survival of primary cultured AML cells at concentrations equivalent to the levels found in the serum of AML patients. Extracellular NM23-H1 protein promoted the in vitro growth and survival of AML cells and this activity was associated with the cytokine production and activation of the MAPK and signal transducers and activators of transcription signaling pathways. Inhibitors specific to MAPK signaling pathways inhibited the growth- and survival-promoting activity of NM23-H1. These findings indicate the novel biological action of extracellular NM23-H1 and its association with poor prognosis, and suggest an important role for extracellular NM23-H1 in the malignant progression of leukemia and a potential therapeutic target for these malignancies.

Extracellular NM23-H1 protein inhibits the survival of primary cultured normal human peripheral blood mononuclear cells and activates the cytokine production

An elevated serum level of NM23-H1 protein is found in acute myelogenous leukemia (AML) and predicts a poor treatment outcome for AML patients. To investigate the potential pathological link between the elevated serum level of this protein and poor prognosis, we examined the extracellular effects of recombinant NM23-H1 protein on the in vitro survival of primary cultured normal peripheral blood mononuclear cells (PBMNC) at concentrations equivalent to the levels found in the serum of AML patients. Extracellular NM23-H1 protein inhibited the in vitro survival of PBMNC and promoted the production of various cytokines, such as GM-CSF and IL-1beta, which in fact promoted the growth of primary cultured AML cells. These findings indicate a novel biological action of extracellular NM23-H1 and its association with poor prognosis of patients with elevated serum levels of NM23-H1 protein. These results suggest an important role of extracellular NM23-H1 in the malignant progression of leukemia and a potential therapeutic target for these malignancies.

SET complex in serous epithelial ovarian cancer

With low cure rates but increasing diverse treatment options that provide variable remission times, ovarian cancer is increasingly being recognized as a chronic disease. This reality indicates the need for a better understanding of factors influencing disease progression. In a previous global analysis of gene expression, we identified genes differentially expressed when comparing serous epithelial ovarian tumors of low and high malignant potential (grade 0 vs grade 3). In this analysis, 4 out of 5 members of the SET complex, SET, APE1, NM23 and HMGB2, were highly expressed in invasive grade 3 tumors. To further investigate the expression of these genes and the fifth member of the SET complex (pp32), we performed immunohistochemistry, on a tissue array composed of 235 serous tumors of different grades and disease stages. A significant correlation between expression of all SET complex proteins and the tumor differentiation was observed (p < 0.05). When combining all tumors, overexpression of Nm23 (p = 0.04), Set (p = 0.004) and Ape1 (p = 0.004) was associated with the clinical stage of the disease. No marker by itself was associated with prognosis. The combination of a high level of Nm23 in the context of a low level of Set compared to all other combinations of these markers did confer a better prognosis (p = 0.03). When combined, high expression of Hmgb2 and low expression of Ape1 was also associated with patient prognosis (p = 0.05). These findings suggest that a strategy that sums the activities of different partners within a pathway may be more appropriate in designing nomograms for patient stratification.

Clinical significance of serum NM23-H1 protein in neuroblastoma

We have previously reported that NM23 genes are overexpressed in various hematological malignancies and that serum NM23-H1 protein levels are useful for predicting patient outcomes. In this study we assessed the clinical implications of serum NM23-H1 protein on neuroblastoma. We examined serum NM23-H1 protein levels in 217 patients with neuroblastoma, including 131 found by mass-screening and 86 found clinically by an enzyme-linked immunosorbent assay, and determined the association between levels of this protein, and known prognostic factors or the clinical outcome. The serum NM23-H1 protein level was higher in neuroblastoma patients than in control children (P < 0.0001). Patients with MYCN amplification had higher serum NM23-H1 levels than those with a single copy of MYCN. Overall survival was assessed in the 86 patients found clinically, and was found to be worse in patients with higher serum MN23-H1 levels (> or = 250 ng/mL) than in those with lower levels (< 250 ng/mL; P = 0.034). The higher level of NM23-H1 was correlated with a worse outcome in patients with a single MYCN copy, or in those younger than 12 months of age. Serum NM23-H1 protein levels may contribute to predictions of clinical outcome in patients with neuroblastoma.

Translational control of putative protooncogene Nm23-M2 by cytokines via phosphoinositide 3-kinase signaling

The expansion and differentiation of hematopoietic progenitors is regulated by cytokine and growth factor signaling. To examine how signal transduction controls the gene expression program required for progenitor expansion, we screened ATLAS filters with polysome-associated mRNA derived from erythroid progenitors stimulated with erythropoietin and/or stem cell factor. The putative proto-oncogene nucleoside diphosphate kinase B (ndpk-B or nm23-M2) was identified as an erythropoietin and stem cell factor target gene. Factor-induced expression of nm23-M2 was regulated specifically at the level of polysome association by a phosphoinositide 3-kinase-dependent mechanism. Identification of the transcription initiation site revealed that nm23-M2 mRNA starts with a terminal oligopyrimidine sequence, which is known to render mRNA translation dependent on mitogenic factors. Recently, the nm23-M2 locus was identified as a common leukemia retrovirus integration site, suggesting that it plays a role in leukemia development. The expression of Nm23 from a retroviral vector in the absence of its 5'-untranslated region caused constitutive polysome association of nm23-M2. Polysome-association and protein expression of endogenous nm23-M2 declined during differentiation of erythroid progenitors, suggesting a role for Nm23-M2 in progenitor expansion. Taken together, nm23-m2 exemplifies that cytokine-dependent control of translation initiation is an important mechanism of gene expression regulation.

12-O-Tetradecanoylphorbol-13-acetate and UV Radiation-induced Nucleoside Diphosphate Protein Kinase B Mediates Neoplastic Transformation of Epidermal Cells

The molecular changes associated with early skin carcinogenesis are largely unknown. We have previously identified 11 genes whose expression was up- or down-regulated by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse skin keratinocyte progenitor cells (Wei, S.-J., Trempus, C. S., Cannon, R. E., Bortner, C. D., and Tennant, R. W. (2003) J. Biol. Chem. 278, 1758-1768). Here, we show an induction of a nucleoside diphosphate protein kinase B (NDPK-B) gene in response to TPA or UV radiation (UVR). TPA or UVR significantly induced the expression of NDPK-B both in vivo hyperplastic mouse skin and in vitro mouse JB6 Cl 41-5a epidermal cells. Indeed, this gene was also up-regulated in TPA or UVR-mediated skin tumors including papillomas, spindle cell tumors, and squamous cell carcinomas, relative to adjacent normal skins. Functional studies by constitutive expression of nm23-M2/NDPK-B in TPA susceptible JB6 Cl 41-5a and TPA-resistant JB6 Cl 30-7b preneoplastic epidermal cell lines showed a remarkable gene dosage-dependent increase in foci-forming activity, as well as an enhancement in the efficiency of neoplastic transformation of these cells in soft agar but no effect on proliferation in monolayer cultures. Interestingly, stable transfection of the nm23-M2/NDPK-B del-RGD or G106A mutant gene in JB6 Cl 41-5a cells selectively abrogated NDPK-B-induced cellular transformation, implicating a possible Arg105-Gly106-Asp107 regulatory role in early skin carcinogenesis.

Physiological and pathological relevance of extracellular NM23/NDP kinases

The NM23 gene is overexpressed in many hematological malignancies and other neoplasms. Some tumor cell lines that overexpress NM23 secrete this protein into extracellular environment. In this study, we found that the serum concentration of NM23-H1 protein was significantly higher in patients with various hematological malignancies. The serum level of NM23-H1 protein was clinically useful as a prognostic factor in malignant lymphoma and acute myelogeneous leukemia (AML). The level of NM23-H1 protein in all of the normal serum samples examined was lower than 10 ng/mL, while those in the tumors varied from about 0 to 1000 ng/mL. Exogenously added NM23-H1 protein did not affect the growth or survival of various leukemia and lymphoma cell lines. However, NM23-H1 protein inhibited the survival of adherent normal peripheral blood mononuclear cells (PBMNC) at 100-1000 ng/mL, and slightly stimulated the survival of nonadherent PBMNC. These results suggest that the effect of NM23-H1 protein on normal PBMNC may be associated with a poor prognosis in hematological malignancies.

Clinical significance of nm23-H1 proteins expressed on cell surface in non-Hodgkin's lymphoma

The nm23 gene was isolated as a metastasis suppressor gene that exhibits low expression in high-level metastatic cancer cells. Its gene is related to the prognosis of acute myelogenous leukemia (AML) and non-Hodgkin's lymphoma (NHL). In this study, we examined the expression of nm23-H1 protein on the lymphoma cell surface of NHL. In 28 of 108 cases (25.9%), we observed > or = 20% of cell surface nm23-H1 protein expression and expression was especially high in peripheral T cell lymphomas and extranodal NK/T cell lymphomas. We also observed a significant correlation between serum nm23-H1 level and cell surface nm23-H1 expression levels. In patients with high levels of cell surface nm23-H1 expression, overall and progression-free survival rates were significantly lower than those in patients with low surface nm23-H1 expression levels. When surface nm23-H1 and serum nm23-H1 were combined, patients with high levels of both exhibited a poorer prognosis than patients with a high level of one or the other. These results indicate that in addition to serum nm23-H1, cell surface nm23-H1 may be used as a prognostic factor in planning a treatment strategy. The nm23-H1 protein appears to be intimately related to biological aggressiveness of lymphoma and, therefore, might be a molecular target of NHL treatment.

Extracellular nucleoside diphosphate kinase NM23/NDPK modulates normal hematopoietic differentiation

OBJECTIVE

We previously demonstrated the presence of nucleoside diphosphate kinase NDPK/NM23 in normal human plasma. It also was reported that extracellular NM23 could inhibit differentiation of certain hematopoietic cell lines. We further investigated the extracellular effect of NM23 on hematopoiesis by adding recombinant NM23-H1, NM23-H2, and NM23-H3 proteins to in vitro differentiation assays of normal human hematopoietic progenitors.

MATERIALS AND METHODS

To study the effect on the earlier stages of hematopoietic maturation, NM23 was added to serum-free pre-colony-forming unit (pre-CFU) assays starting from immature CD34++CD38- bone marrow cells. Serum-free CFU assays starting from CD34+ CD38+ bone marrow cells were used as a model for terminal hematopoietic differentiation.

RESULTS

In pre-CFU assays, none of the NM23 isoforms used significantly changed the expansion of CD34++CD38- cells, nor did NM23 alter the CD34++ CD38- cell lineage commitment. In contrast, terminal differentiation of CD34+CD38+ progenitor cells in CFU assays was significantly altered by addition of NM23 protein. More erythroid burst-forming units and fewer macrophage colonies were observed in cultures containing any of the NM23 isoforms examined. Similar effects were observed using the enzymatically inactive H118N mutant of NM23-H1, strongly suggesting that the observed effect is independent of the nucleoside diphosphate kinase activity of NM23.

CONCLUSION

We demonstrated a modulating effect of extracellular NM23 proteins on the terminal stages of normal hematopoietic differentiation. Therefore, the fairly high concentrations of NM23 constitutively present in plasma could have a physiologic role in supporting erythropoiesis and inhibiting excessive macrophage formation.

Expression of cell surface NM23 proteins of human leukemia cell lines of various cellular lineage and differentiation stages

Cell surface expression of NM23 protein is only observed on tumor cell lines, but not on normal cells. To examine what types of tumor cell line express the cell surface NM23 protein, we measured the cell surface NM23-H1 and NM23-H2 proteins of leukemia line cells on various cellular lineage and differentiation stages. The NM23-H1 was expressed on myeloid leukemia lines but not lymphoid lines, while NM23-H2 was only expressed on erythroleukemia lines. The complement-dependent cytolysis confirmed the expression of these proteins on the surface. Surface NM23-H1 and NM23-H2 proteins were decreased during in vitro erythroid and granulocyte differentiation. These results show that the surface expression of NM23 proteins is related to cellular lineage and differentiation stage of leukemia line cells.

Serum nm23-H1 protein as a prognostic factor in hematological malignancies

A nondifferentiating mouse myeloid leukemia cell line produces differentiation-inhibiting factors. One of these factors was purified as a homologue of nm23. The nm23 gene was isolated as a metastasis-suppressor gene that exhibits low expression in high-level metastatic cancer cells. The nm23 gene was overexpressed in acute myelogenous leukemia (AML) cells and a higher level of nm23-H1 expression was correlated with a poor prognosis in AML. Multivariate analysis of putative prognostic factors revealed that elevated nm23-H1 mRNA levels significantly contributed to the prognosis of patients with AML. The overexpression of nm23-H1 was also observed in various hematological neoplasms. To use nm23 overexpression to determine the prognosis for lymphoma, we established an enzyme-linked immunosorbent assay (ELISA) technique to determine the serum level of nm23-H1 protein. This assay is far simpler than that used to determine nm23 mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR). Using this system, we measured nm23-H1 protein levels in many hematological malignancies. Serum nm23-HI levels were significantly higher in patients with all of the hematological neoplasms tested (AML, chronic myelogenous leukemia, acute lymphoblastic leukemia, (ALL) myelodysplastic syndrome (MDS) and malignant lymphomas) than in normal controls. An elevated serum nm23-H1 protein concentration predicted a poor outcome for AML and non-Hodgkin's lymphoma. Especially in diffuse large B-cell lymphoma (DLBCL), seram nm23-H1 protein levels were an important prognostic factor in planning an appropriate treatment strategy for DLBCL. The serum nm23-H I protein levels probably depend on the total mass of malignant cells overexpressing nm23-H1.

Elevated plasma level of differentiation inhibitory factor nm23-H1 protein correlates with risk factors for myelodysplastic syndrome

We measured plasma nm23-H1 level (nm23-H1), a differentiation inhibitory factor, by an enzyme-linked immunosorbent assay (ELISA) in patients with aplastic anemia (AA) and myelodysplastic syndrome (MDS). The nm23-H1 in AA was not significantly elevated when compared to normal subjects (6.66 +/- 1.20 ng/ml vs 5.13 +/- 0.81 ng/ml; P = 0.274). In contrast, MDS patients had significantly high levels of nm23-H1 compared not only to normal subjects (11.16 +/- 1.42 vs 5.13 +/- 0.81 ng/ml; P = 0.0004) but also to those of the AA group (11.16 +/- 1.42 ng/ml vs 6.66 +/- 1.20 ng/ml; P = 0.018). In the MDS group of patients, no significant difference was observed in the nm23-H1 levels between patients with refractory anemia (RA) and RA with excess blasts (RAEB)/RAEB in transformation (10.71 +/- 1.61 ng/ml vs 9.24 +/- 2.66 ng/ml; P = 0.672). Of the patients with RA, patients with low risk according to the International Prognostic Scoring System (IPSS) had significantly low levels of nm23-H1 compared to those of IPSS INT-1 level cases (6.40 +/- 1.36 ng/ml vs 13.05 +/- 2.50 ng/ml; P = 0.0028), suggesting that nm23-H1 may be useful as a prognostic marker for MDS, especially in low risk patients.

Expression of nm23-H1 in hydatidiform mole and its relationship with the development of postmolar disease

The aim of the present study was to investigate the expression of nm23-H1 in human placenta, hydatidiform mole and choriocarcinoma cells. Nm23-H1 protein was localized in the cytotrophoblast, but not in the syncytiotrophoblast. In the hydatidiform mole cases with subsequent spontaneous remission, nm23-H1 mRNA levels were significantly lower than those in first-trimester placentas. However, its levels were elevated in the hydatidiform mole cases that progressed to persistent gestational trophoblastic disease and were comparable to those of first-trimester placentas, and they were further elevated in choriocarcinoma cells. The present data suggest an association of nm23-H1 for the proliferation activity of trophoblast, and its increased expression may influence the development of persistent trophoblastic disease.

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.

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.

Downregulation of intracellular nm23-H1 prevents cisplatin-induced DNA damage in oesophageal cancer cells: possible association with Na(+), K(+)-ATPase

Previously, we showed that expression of nm23-H1 is associated inversely with sensitivity to cisplatin in human oesophageal squamous cell carcinoma (OSCC). The present study was undertaken to investigate the association of nm23-H1 expression with cisplatin-induced DNA damage in OSCC using antisense nm23-H1 transfectants. YES-2/AS-12, an antisense nm23-H1-transfected OSCC cell line, showed significantly reduced expression of intracellular nm23-H1 protein compared with that in parental YES-2 cells and YES-2/Neo transfectants. Surface expression of nm23-H1 protein was not observed in any of the three cell lines. PCR analysis for DNA damage demonstrated that YES-2/AS-12 cells were more resistant to nuclear and mitochondrial DNA damage by cisplatin than were YES-2/Neo cells. In addition, mitochondrial membrane potentials and DNA fragmentation assays confirmed that YES-2/AS-12 was more resistant than YES-2/Neo to apoptosis induced by cisplatin. In contrast, YES-2/AS-12 was more sensitive to ouabain, a selective inhibitor of Na(+), K(+)-ATPase, than YES-2 and YES-2/Neo. Pre-treatment with ouabain resulted in no differences in cisplatin sensitivity between the three cell lines examined. Intracellular platinum level in YES-2/AS-12 was significantly lower than that in YES-2 and YES-2/Neo following incubation with cisplatin, whereas ouabain pre-treatment resulted in no differences in intracellular platinum accumulations between the three cell lines. Our data support the conclusion that reduced expression of intracellular nm23-H1 in OSCC cells is associated with cisplatin resistance via the prevention of both nuclear and mitochondrial DNA damage and suggest that it may be related to Na(+), K(+)-ATPase activity, which is responsible for intracellular cisplatin accumulation.

Neuroblastoma specific effects of DR-nm23 and its mutant forms on differentiation and apoptosis

DR-nm23 belongs to a gene family which includes nm23-H1, originally identified as a candidate metastasis suppressor gene. Nm23 genes are expressed in different tumor types where their levels have been alternatively associated with reduced or increased metastatic potential. Nm23-H1, -H2, DR-nm23 and nm23-H4 all possess NDP kinase activity. Overexpression of DR-nm23 inhibits differentiation and promotes apoptosis in hematopoietic cells. By contrast, it induces morphological and biochemical changes associated with neural differentiation in neuroblastoma cells. In this study, we show that mutations in the catalytic domain and in the serine 61 phosphorylation site, possibly required for protein-protein interactions, impair the ability of DR-nm23 to induce neural differentiation. Moreover, neuroblastoma cells overexpressing wild-type or mutant DR-nm23 are less sensitive to apoptosis triggered by serum withdrawal. By subcellular fractionation, wild-type and mutant DR-nm23 localize in the cytoplasm and prevalently in the mitochondrial fraction. In co-immunoprecipitation experiments, wild-type DR-nm23 binds other members of nm23 family, but mutations in the catalytic and in the RGD domains and in serine 61 inhibit the formation of hetero-multimers. Thus, the integrity of the NDP kinase activity and the presence of a serine residue in position 61 seem essential for the ability of DR-nm23 to trigger differentiation and to bind other Nm23 proteins, but not for the anti-apoptotic effect in neuroblastoma cells. These studies underline the tissue specificity of the biological effects induced by DR-nm23 expression.

High cyclin-dependent kinase inhibitors in Bcl-2 and Bcl-xL-expressing CD34+-proliferating haematopoietic progenitors

We have previously described the isolation of primitive, slow-proliferating progenitors from normal, circulating CD34+ cells by using the fluorescent dye 5-6-carboxyfluorescein diacetate succinimidyl ester (CFDA-SE). CFDA-SE(bright) (primitive) and CFDA-SE(dim) (differentiating) cells were isolated following cytokine stimulation on the basis of their different proliferation rates. In the present work we analysed the expression levels of a number of proteins involved with differentiation, proliferation and survival/apoptosis in CFDA-SE(bright)/CD34+/slow-proliferating cells that were previously defined as progenitors capable of differentiating into different lineages. The aim of this work was to gain a better understanding of our model system in order to define some of the important parameters that regulate differentiation in haematopoietic progenitors. GATA-1 and PU.1 RNA levels were similar in freshly isolated (d 0) CD34+ and in CFDA-SE(bright) (bright) cells, whereas they increased in CFDA-SE(dim) (dim) cells. Accordingly, Nm23 was expressed at higher levels in bright cells. Moreover, bright cells had higher p21WAF1/CIP1, p27KIP1 and p16Ink4 protein levels than dim cells. Consistently, Cdc2 and Cdk2 kinase activity was much higher in the dim than in the slower proliferating bright cells. C-myc and p53 levels were higher in bright cells than in d 0 CD34+ and dim cells, and so was Bcl-xL, which followed the trend we have previously described for Bcl-2. Thus, bright cells, despite having a higher proliferation rate than the starting d 0 CD34+ population, have strikingly elevated levels of cyclin-dependent kinase inhibitors, which are likely to also act as inhibitors of differentiation.

The human Nm23/nucleoside diphosphate kinases

Biochemical experiments over the past 40 years have shown that nucleoside diphosphate (NDP) kinase activity, which catalyzes phosphoryl transfer from a nucleoside triphosphate to a nucleoside diphosphate, is ubiquitously found in organisms from bacteria to human. Over the past 10 years, eight human genes of the nm23/NDP kinase family have been discovered that can be separated into two groups based on analysis of their sequences. In addition to catalysis, which may not be exhibited by all isoforms, evidence for regulatory roles has come recently from the discovery of the genes nm23 and awd, which encode NDP kinases and are involved in tumor metastasis and Drosophila development, respectively. Current work shows that the human NDP kinase genes are differentially expressed in tissues and that their products are targeted to different subcellular locations. This suggests that Nm23/NDP kinases possess different, but specific, functions within the cell, depending on their localization. The roles of NDP kinases in metabolic pathways and nucleic acid synthesis are discussed.

nm23: unraveling its biological function in cell differentiation

Tumor suppressor genes have a pivotal role in normal cells regulating cell cycle processes negatively. Furthermore, the inhibition of cell proliferation is a crucial step in the achievement of cell differentiation. Increasing evidence suggests that the nm23 genes, initially documented as suppressors of the invasive phenotype in some cancer types, are involved in the control of normal development and differentiation. In this review, we summarize some data concerning the involvement of the nm23 genes in development and differentiation, attempting to delineate an overall view of many facets of their biological role.

Prognostic Implications of the Differentiation Inhibitory Factornm23-H1 Protein in the Plasma of Aggressive Non-Hodgkin’s Lymphoma

The outcome of patients with non-Hodgkin’s lymphoma has been improved by current approaches to treatment. Nevertheless, many patients either do not have a complete remission or ultimately relapse. To identify such patients, it is important to be able to predict the outcome. We previously found that the differentiation inhibitory factor/nm23 was correlated with the prognosis of acute myeloid leukemia. To examine the prognostic effect of nm23 on non-Hodgkin’s lymphoma, we established an enzyme-linked immunosorbent assay procedure to determine nm23-H1 protein levels in plasma and assessed the association of this protein level with the response to chemotherapy, overall survival, and progression-free survival in patients with aggressive non-Hodgkin’s lymphoma. The plasma concentration of nm23-H1 was significantly higher in patients with malignant lymphoma than in normal controls, especially in aggressive non-Hodgkin’s lymphoma. The complete remission rate in patients with higher nm23-H1 levels was significantly worse than that in patients with lower nm23-H1 levels. Overall survival and progression-free survival were also lower in patients with higher nm23-H1 levels than in those with lower levels. The 3-year survival rates in patients with low and high nm23-H1levels were 79.5% and 6.7% (P = .0001). A multivariate analysis of prognostic factors showed that the plasma nm23-H1level was independently associated with the survival and progression-free survival. An elevated plasma nm23-H1concentration predicts a poor outcome of advanced non-Hodgkin’s lymphoma. Therefore, nm23-H1 in plasma may be useful for identifying a distinct group of patients at very high risk.

Organization and expression of mouse nm23-M1 gene. Comparison with nm23-M2 expression

Nm23 is a gene family encoding different isoforms of the nucleotide diphosphate kinase (NDPK), an enzyme involved in the synthesis of nucleoside triphosphates. In the present study, the organization and expression of the nm23-M1 gene encoding the mouse NDPKA isoform are described. This gene is about 10kb long and composed of five exons. The organization and the exon-intron boundaries are strictly conserved as compared to the human and rat related genes. The gene promoter region did not exhibit any consensus TATA box, SP1 binding element or Inr sequence. By contrast, TCF-1/LEF-1 binding elements and Pit-1 consensus sequence were present. Northern blotting and in situ hybridization methods were carried out in adult and 18.5 days post-coitum (dpc) mouse embryo, respectively. They showed tissue-specific expression of nm23-M1 transcripts, despite housekeeping gene promoter features. The strongest signals were detected in the nervous system, sensory organs and embryonic thymus. In contrast nm23-M2 mRNA was shown to be more widely expressed.The relationship between nm23-M1 gene tissue-specific expression and the putative binding element of the promoter region is discussed.

Inosine monophosphate dehydrogenase: A molecular switch integrating pleiotropic GTP-dependent beta-cell functions

Studies of pancreatic islet function in the pathogenesis of type 2 diabetes mellitus have tended to focus on the short-term control of insulin secretion. However, the long-term control of beta-cell mass is also relevant to diabetes, since this parameter is reduced substantially even in non-insulin-dependent diabetes in humans. In animal models of type 2 diabetes, the normal balance between beta-cell proliferation and programmed cell death is perturbed. We take the perspective in this overview that inosine monophosphate dehydrogenase (IMPDH; EC 1.1.1. 205) may represent a previously neglected molecular integrator or sensor that exerts both functional (secretory) and anatomical (proliferative) effects within beta-cells. These properties reflect the fact that IMPDH is a rate-limiting enzyme in the new synthesis of the purine guanosine triphosphate (GTP), which modulates both exocytotic insulin secretion and DNA synthesis, as well as a number of other critical cellular functions within the beta-cell. Alterations in the expression or activity of IMPDH may be central to beta-cell replication, cell cycle progression, differentiation, and maintenance of adequate islet mass, effects that are probably mediated both by GTP directly, and indirectly via low molecular mass GTPases. If GTP becomes depleted, a hierarchy of beta-cell functions becomes progressively paralyzed, until eventually the effete cell is removed via apoptosis.

Nucleoside diphosphate kinase activity in soluble transducin preparations biochemical properties and possible role of transducin-beta as phosphorylated enzyme intermediate

Known nucleoside diphosphate kinases (NDPKs) are oligomers of 17-23-kDa subunits and catalyze the reaction N1TP + N2DP --> N1DP + N2TP via formation of a histidine-phosphorylated enzyme intermediate. NDPKs are involved in the activation of heterotrimeric GTP-binding proteins (G-proteins) by catalyzing the formation of GTP from GDP, but the properties of G-protein-associated NDPKs are still incompletely known. The aim of our present study was to characterize NDPK in soluble preparations of the retinal G-protein transducin. The NDPK is operationally referred to as transducin-NDPK. Like known NDPKs, transducin-NDPK utilizes NTPs and phosphorothioate analogs of NTPs as substrates. GDP was a more effective phosphoryl group acceptor at transducin-NDPK than ADP and CDP, and guanosine 5'-[gamma-thio]triphosphate (GTP[S]) was a more effective thiophosphoryl group donor than adenosine 5'-[gamma-thio]triphosphate (ATP[S]). In contrast with their action on known NDPKs, mastoparan and mastoparan 7 had no stimulatory effect on transducin-NDPK. Guanosine 5'-[beta, gamma-imido]triphosphate (p[NH]ppG) potentiated [3H]GTP[S] formation from [3H]GDP and ATP[S] but not [3H]GTP[S] formation from [3H]GDP and GTP[S]. Depending on the thiophosphoryl group acceptor and donor, [3H]NTP[S] formation was differentially regulated by Mg2+, Mn2+, Co2+, Ca2+ and Zn2+. [gamma-32P]ATP and [gamma-32P]GTP [32P]phosphorylated, and [35S]ATP[S] [35S]thiophosphorylated, a 36-kDa protein comigrating with transducin-beta. p[NH]ppG potentiated [35S]thiophosphorylation of the 36-kDa protein. 32P-labeling of the 36-kDa protein showed characteristics of histidine phosphorylation. There was no evidence for (thio)phosphorylation of 17-23-kDa proteins. Our data show the following: (a) soluble transducin preparations contain a GDP-prefering and guanine nucleotide-regulated NDPK; (b) transducin-beta may serve as a (thio)phosphorylated NDPK intermediate; (c) transducin-NDPK is distinct from known NDPKs and may consist of multiple kinases or a single kinase with multiple regulatory domains.

Cytoskeletal association of the A and B nucleoside diphosphate kinases of interphasic but not mitotic human carcinoma cell lines: specific nuclear localization of the B subunit

The human A and B subunits of nucleoside diphosphate kinase (NDP kinase), encoded by the nm23-H1 and nm23-H2 genes, respectively, associate as homo- or heterohexamers to be catalytically active for the synthesis of nucleoside triphosphates. Despite 88% identity, they appear to possess specific functions. The nm23-H1 gene is implicated in tumor progression and metastasis, and the nm23-H2 gene product is a transcription factor for c-myc. To determine if these distinct functions reflect different subcellular localizations, the distribution of the A and B NDP kinases was analyzed by immunocytofluorescence microscopy in human breast cancer cell lines (MCF-7 and MDA-MB-231) using highly specific polyclonal and monoclonal antibodies. Interphasic cells exhibited a granular and filamentous cytoplasmic staining, particularly intense around nuclei, with both anti-NDP kinase A and B antibodies. The filamentous component observed with either anti-A or anti-B antibodies was altered in parallel to tubulin labeling with compounds interacting with microtubules, such as taxol and colchicine. Confirming published biochemical data, a partial colocalization with the vimentin network was observed in the MDA-231 cell line. A nuclear and nucleolar localization of NDP kinase B was shown by confocal microscopy which was not observed with the A enzyme. In dividing cells, NDP kinase labeling was punctiform and was not colocalized with the mitotic spindle. In conclusion, the A and B NDP kinases are similarly distributed in cytosol, associated partly to microtubules supporting a role in nucleotide channeling. Only the B enzyme is present in nuclei in accord with its role as a DNA binding protein. Their altered localization in dividing cells suggests colocalization with yet unidentified structures which are not intermediate filament aggregates.