Expression of a catalytically inactive H118Y mutant of nm23-H2 suppresses the metastatic potential of line IV Cl 1 human melanoma cells

Nm23-H1 and nm23-H2 are putative metastasis suppressor genes that encode nucleoside diphosphate kinase (NDPK) A and B. NDPKs form oligomers distributed between soluble and particulate fractions of cells and therefore may exert their effects as either soluble or bound proteins. To determine whether metastasis-related functions of NDPKs are mediated by their catalytic activity in membrane bound or soluble complexes, we have stably transfected highly metastatic human melanoma Line IV Cl 1 cells with wild-type and catalytically inactive (H118Y) nm23-H1 and nm23-H2 genes and assayed their metastatic potential in nude mice. Transfection with wild-type nm23-H1 and nm23-H2 genes and catalytically inactive nm23-H1 did not significantly (all p > 0.10) alter the metastatic potential of Line IV Cl 1 cells while transfection with catalytically inactive nm23-H2 significantly (p < 0.01) reduced their metastatic potential. The lack of effect of transfection with wild-type and catalytically inactive nm23-H1 suggests that neither soluble nor membrane bound NDPK A affect the metastatic potential of Line IV Cl 1 cells. The metastasis suppressive effect of catalytically inactive NDPK B overexpression suggests that competition with bound complexes containing catalytically active NDPK B inhibits metastasis of Line IV Cl 1 cells. These results imply that bound NDPK B promotes metastasis and suggest that inhibition of its function or of its binding to critical sites may be a useful approach to limit the development of metastases in human melanoma.

Overexpression of NM23-1 enhances responsiveness of IMR-32 human neuroblastoma cells to differentiation stimuli

BACKGROUND

Aggressiveness of neuroblastoma is associated with increased expression of the putative metastasis suppressor genes, nm23-1 and nm23-2. These genes encode nucleoside diphosphate kinases A and B that form free or bound homo- and heteromers, which are distributed between soluble and particulate fractions of cells and display catalytic and non-catalytic activities.

MATERIALS AND METHODS

In order to establish which forms and activities of nm23 proteins are operative in neuroblastoma we stably transfected IMR-32 human neuroblastoma cells with constructs encoding wild type and catalytically inactive nm23-1 and nm23-2 proteins.

RESULTS

Overexpression of wild type nm23-1 proteins stimulated spontaneous neurite outgrowth and enhanced differentiation in response to serum starvation and retinoic acid. In contrast, overexpression of the catalytically inactive nm23-1T mutant enhanced TPA-mediated inhibition of differentiation.

CONCLUSION

Our findings suggest that differentiation associated functions of nm23 proteins in IMR-32 neuroblastoma cells are carried out by bound nm23-1 proteins docked in a limited number of nm23-1 specific sites.

Nm23-transfected MDA-MB-435 human breast carcinoma cells form tumors with altered phospholipid metabolism and pH: a 31P nuclear magnetic resonance study in vivo and in vitro

Nm23 genes are involved in the control of the metastatic potential of breast carcinoma cells. To understand the impact of nm23 genes on tumor physiology and metabolism, a 31P nuclear magnetic resonance (NMR) spectroscopic study was performed on tumors formed in the mammary fat pad of severe combined immunodeficiency mice by MDA-MB-435 human breast carcinoma cells transfected with cDNA encoding wild type nm23-H1 and nm23-H2 proteins. Tumors formed by MDA-MB-435 cells transfected with vector alone were used as controls. All transgene tumors exhibited significantly higher levels of phosphodiester (PDE) compounds relative to phosphomonoester (PME) compounds in vivo compared with control tumors. Similar differences in PDE and PME also were observed for spectra obtained from cells growing in culture. Intracellular pH was significantly lower and extracellular pH was significantly higher for transgene tumors compared with control tumors. Histologic analysis of lung sections confirmed reductions in incidence, number, and size of metastatic nodules for animals bearing transgene tumors. These results suggest that nm23 genes may affect suppression of metastasis through phospholipid-mediated signaling and cellular pH regulation.

Nm23-transfected MDA-MB-435 human breast carcinoma cells form tumors with altered phospholipid metabolism and pH: a 31P nuclear magnetic resonance study in vivo and in vitro

Nm23 genes are involved in the control of the metastatic potential of breast carcinoma cells. To understand the impact of nm23 genes on tumor physiology and metabolism, a 31P nuclear magnetic resonance (NMR) spectroscopic study was performed on tumors formed in the mammary fat pad of severe combined immunodeficiency mice by MDA-MB-435 human breast carcinoma cells transfected with cDNA encoding wild type nm23-H1 and nm23-H2 proteins. Tumors formed by MDA-MB-435 cells transfected with vector alone were used as controls. All transgene tumors exhibited significantly higher levels of phosphodiester (PDE) compounds relative to phosphomonoester (PME) compounds in vivo compared with control tumors. Similar differences in PDE and PME also were observed for spectra obtained from cells growing in culture. Intracellular pH was significantly lower and extracellular pH was significantly higher for transgene tumors compared with control tumors. Histologic analysis of lung sections confirmed reductions in incidence, number, and size of metastatic nodules for animals bearing transgene tumors. These results suggest that nm23 genes may affect suppression of metastasis through phospholipid-mediated signaling and cellular pH regulation.

Identification of a new class of protein kinases represented by eukaryotic elongation factor-2 kinase

The several hundred members of the eukaryotic protein kinase superfamily characterized to date share a similar catalytic domain structure, consisting of 12 conserved subdomains. Here we report the existence and wide occurrence in eukaryotes of a protein kinase with a completely different structure. We cloned and sequenced the human, mouse, rat, and Caenorhabditis elegans eukaryotic elongation factor-2 kinase (eEF-2 kinase) and found that with the exception of the ATP-binding site, they do not contain any sequence motifs characteristic of the eukaryotic protein kinase superfamily. Comparison of different eEF-2 kinase sequences reveals a highly conserved region of approximately 200 amino acids which was found to be homologous to the catalytic domain of the recently described myosin heavy chain kinase A (MHCK A) from Dictyostelium. This suggests that eEF-2 kinase and MHCK A are members of a new class of protein kinases with a novel catalytic domain structure.

The crystal structure of a human nucleoside diphosphate kinase, NM23-H2

The 2.8 A resolution X-ray structure of NM23-H2 has been determined by molecular replacement using the structure of Myxococcus xanthus nucleoside diphosphate (NDP) kinase. NM23-H2 is a human NDP kinase. The enzyme catalyses phosphoryl transfer, binds DNA, and can activate the transcription of the c-myc oncogene in vitro. NM23 has also been reported to be a suppressor of metastasis in some types of tumours. Whereas the M. xanthus NDP kinase is a tetramer, NM23-H2 is a hexamer. The fold of NM23-H2 is identical to the fold of other NDP kinases. Two antiparallel helices joined by a turn form one edge of the nucleotide binding cleft. This region moves in a hinge-like fashion in response to substrate binding and crystal packing forces. Additional differences in conformation among the NDP kinases are principally in regions involved in protein-protein contacts within the oligomers. The only protein-protein interaction conserved among all NDP kinases is a dimeric interaction. Several mutations of NM23-H2 have been detected in tumour tissues. These mutations do not involve residues interacting with the substrates, and probably destabilise the enzyme without directly affecting the catalytic activity. Low level phosphorylation of serines has been reported for NM23 both in vitro and in vivo. The structure of the hexamer indicates that two serine residues that have been reported as being phosphorylated, Ser44 and Ser122, are on the surface of the hexamer, and are likely to be phosphorylated by exogenous kinases. In contrast, Ser120 is buried, and is most likely phosphorylated by a direct transfer from the phosphohistidine intermediate of the reaction mechanism.

Differential expression and mutation of NME genes in autologous cultured human melanoma cells with different metastatic potentials

The putative metastasis suppressor genes, NME1(nm23-1) and NME2(nm23-2), were examined in a model system we developed to approximate the dissemination of melanoma from a primary skin tumor. We utilized two autologous human melanoma cell lines, IV Cl 1 and IV Cl 3, which displayed qualitatively different metastatic phenotypes following subdermal inoculation into nude mice. Highly metastatic IV Cl 1 cells expressed approximately 5 fold lower levels of protein encoded by NME genes than non-metastatic IV Cl 3 cells. Similar differences in NME protein levels were observed in tumors induced by the two cell lines in nude mice. There were no differences in NME mRNA levels between these two cell lines, suggesting that expression of these proteins is regulated at a post-transcriptional level. We found a ser122-pro mutation in the NME2 gene of metastatic IV Cl 1 cells. A similar ser120-gly mutation in NME1 has been found in human neuroblastoma, suggesting that mutation in this region may be a general phenomenon related to tumor progression. These mutations may have functional consequences since they eliminate potential phosphorylation sites and may affect the tertiary structure of mature protein complexes.

Effects of 5 alpha-dihydrotestosterone (DHT) on the transcription of nm23 and c-myc genes in human prostatic LNCaP cells

Proliferation of the androgen-dependent human prostate LNCaP cells was increased by the androgen DHT. Changes in the steady state level of the nm23 and c-myc mRNA in LNCaP cells, with or without 10 nM DHT, showed the nm23 mRNA to change rapidly, beginning to rise after 2 h and reaching its peak by 4 h of DHT treatment. In contrast, increases in the c-myc gene only became apparent after 4 h of treatment. Maximal increase of nm23 mRNA was observed at 10(-9) M DHT. The basal expression of c-myc and nm23 mRNAs was between 30-70% lower in the LNCaP cells, as compared with the androgen-independent PC-3 and JCA-1 human prostatic human carcinoma cells. Thus nm23 may be classified as a member of the early androgen-responsive genes.

Loss of heterozygosity and decreased expression of NME genes correlate with teratomatous differentiation in human male germ cell tumors

Embryonal carcinoma in the human male is a pluripotential germ cell tumor (GCT), which is suggested to further differentiate to teratoma which displays somatic differentiation representing all three germinal layers. In a panel of 37 GCTs we determined frequency of loss of heterozygosity (LOH) and the level of expression of nucleoside diphosphate kinase (NDPK) genes NME 1 and NME 2. The frequency of LOH in teratomas (86%) was found to be highly significant (P < 0.01) compared to embryonal carcinomas (17%). We also found that the NME encoded proteins are expressed at a 4-5 fold lower level in teratomas compared to embryonal carcinomas. These findings lead us to hypothesize that a critical level of NDPK may be necessary for suppression of aberrant somatic differentiation.

Chromosomal localization and nucleoside diphosphate kinase activity of human metastasis-suppressor genes NM23-1 and NM23-2

Human metastasis-suppressor genes nm23-1 (NME1) and nm23-2 (NME2) are implicated in control of the metastatic potential of malignant cells. Using somatic cell hybrid analysis and fluorescence in situ hybridization we co-localized both genes to 17q21.3. The 17q21 region carries the locus responsible for early-onset familial breast-ovarian cancer and several other genes that are involved in tumorigenesis and differentiation and undergo frequent rearrangements during neoplastic development. Thus, our mapping places the NME genes in a region that may be subjected to multiple selection pressures. NME1 and NME2 genes were expressed as soluble proteins in a T7 bacterial expression system. Both proteins are independently active nucleotide diphosphate kinases and readily form intra- and intermolecular disulfide bonds. The biochemical properties of these proteins may explain the diversity of mature eucaryotic nucleoside diphosphate kinases.

The HIV-1 nef protein does not have guanine nucleotide binding, GTPase, or autophosphorylating activities

Recombinant HIV-1 Nef proteins with either thr-15 or ala-15 have been constructed and expressed in the T7 bacterial system. From the soluble portion of bacterial lysates both Nef(thr-15) and Nef(ala-15) have been purified to near homogeneity through 6 nondenaturing chromatographic steps in the presence of MgCl2. Neither purified proteins display the previously reported GTP binding activity. Additionally Nef(thr-15) does not have autophosphorylating activity with either [gamma-32P]GTP or [gamma-32P]ATP. Although GTPase activity is present in the preparations of Nef proteins, it does not increase during purification and is attributed to bacterial contaminations.

Lovastatin blocks N-ras oncogene-induced neuronal differentiation

ras p21 must be posttranslationally processed in order to be localized to the inner plasma membrane. The first obligatory processing step is the farnesylation of ras p21. Lovastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, may prevent the farnesylation of de novo synthesized ras p21. We demonstrate that N-ras oncogene-induced neuronal differentiation of UR61J rat pheochromocytoma cells is blocked by lovastatin. Our data show that this effect is due to the inhibition of ras p21 farnesylation. The results suggest that ras oncogene-induced phenotype in mammalian cells may be eliminated by preventing the proper processing of ras p21.