Loss of heterozygosity of the nm23-H1 gene in human renal cell carcinomas

Interaction between Nm23 and the tumor suppressor VHL

Among the anti-tumor genes (tumor suppressors and metastasis suppressors), the von-Hippel Lindau gene and the Nm23 family of genes are among the more intriguing ones. Both are small (long and short forms of VHL are 30 and 19 kD, respectively, and Nm23 is ~17 kD), and both possess diverse molecular and cellular functions. Despite extensive studies, the entire spectra of functions and the molecular function-phenotype correlation of these two proteins have not been completely elucidated. In this report, we present data showing these two proteins interact physically. We also summarize and confirm the previous studies that demonstrated the endocytic function of these two genes and further show that the endocytic function of VHL is mediated through the activity of Nm23. These functional and molecular interactions are evolutionarily conserved from Drosophila to human.

MDM2 interacts with NME2 (non-metastatic cells 2, protein) and suppresses the ability of NME2 to negatively regulate cell motility

MDM2 expression, combined with increased p53 expression, is associated with reduced survival in several cancers, but is particularly of interest in renal cell carcinoma (RCC) where evidence suggests the presence of tissue-specific p53/MDM2 pathway defects. We set out to identify MDM2-interacting proteins in renal cells that could act as mediators/targets of MDM2 oncogenic effects in renal cancers. We identified the non-metastatic cells 2, protein; NME2 (NDPK-B, NM23-B/-H2), a nucleoside diphosphate kinase, as an MDM2-interacting protein using both a proteomic-based strategy [affinity chromatography and tandem mass spectrometry [MS/MS] from HEK293 cells] and a yeast two-hybrid screen of a renal carcinoma cell-derived complementary DNA library. The MDM2-NME2 interaction is highly specific, as NME1 (87.5% amino acid identity) does not interact with MDM2 in yeast. Specific NME proteins display well-documented cell motility and metastasis-suppressing activity. We show that NME2 contributes to motility suppression under conditions where MDM2 is expressed at normal physiological/low levels. However, up-regulation of MDM2 in RCC cells abolishes the ability of NME2 to suppress motility. Significantly, when MDM2 expression is down-regulated in these cells using small interfering RNA, the motility-suppressing activity of NME2 is rescued, confirming that MDM2 expression causes the loss of NME2 cell motility regulatory function. Thus MDM2 up-regulation in renal cancer cells can act in a dominant manner to abrogate the function of a potent suppressor of motility and metastasis. Our studies identify a novel protein-protein interaction between MDM2 and NME2, which suggests a mechanism that could explain the link between MDM2 expression and poor patient survival in RCC.

Downstream targets of Nm23-H1: gene expression profiling of CAL 27 cells using DNA microarray

The human nm23-H1 was discovered as a tumor metastasis suppressor based on its reduced expression in melanoma cell lines with low versus high metastatic potential. It encodes for one of two subunits of the nucleoside-diphosphate kinase. Besides its role in the maintenance of the cells NTP pool, nm23 plays a key role in different cellular processes. The role of nm23-H1 in these processes still has to be elucidated. Our goal was to identify Nm23-H1 downstream targets by subjecting Nm23-H1 overexpressing CAL 27 cells oral squamous cell carcinoma (OSSC) to microarray analysis. The genes with changed expression patterns could be clustered into several groups: transforming growth factor beta (TGFbeta) signaling pathway, cell adhesion, invasion and motility, proteasome machinery, cell-cycle, epithelial structural and related molecules and others. Based on the expression patterns observed we presume that nm23-H1 might have a role in OSSCs, which should be confirmed by future experiments.

nm23-H1 expression and loss of heterozygosity in colon adenocarcinoma

BACKGROUND

The discovery that genetic alterations in oncogenes and tumour suppressor genes accompany tumour formation in many human tumours has encouraged the search for genes that promote or suppress tumour spread and metastasis; nm23 is a promising candidate for a metastasis suppressing gene.

AIMS

To evaluate whether expression of nm23-H1 protein or loss of heterozygosity (LOH) of the nm23-H1 gene is associated with colon cancer progression.

MATERIALS/METHODS

Paraffin wax embedded tissue sections were analysed immunohistochemically. DNA isolated from normal and tumour tissue was used for LOH analysis using a variable nucleotide tandem repeat (VNTR) marker located in the untranslated 5' region of the nm23-H1 gene. RNA isolated from tumour and normal tissue was used for "real time" RT-PCR.

RESULTS

Of 102 adenocarcinomas examined, 58.8% stained weakly for nm23-H1 protein. There was a negative correlation between nm23-H1 positivity and tumour histological grade. In VNTR analysis, 70.2% of patients were informative and 27.4% of tumours had nm23-H1 LOH. There was a positive correlation between nm23-H1 LOH and both tumour histological grade and Dukes's stage. Expression of nm23-H1 mRNA was increased in 22 of 30 colon tumours compared with normal tissue. No significant correlation was found between nm23-H1 mRNA expression and histological grade or Dukes's stage of tumours.

CONCLUSIONS

These findings suggest that nm23-H1 protein expression in early stages may have a role in suppressing metastasis in sporadic colon cancer, whereas at a later stage both reduced nm23-H1 protein expression and LOH of the nm23-H1 gene may play role in colon cancer progression and metastasis.

Subcellular localization of A and B Nm23/NDPK subunits

The human Nm23-H1/NDPK A and Nm23-H2/NDPK B encode for two subunits of nucleoside diphosphate kinase--a ubiquitous enzyme that transfers the terminal phosphates from ATP to (d)NDPs. Although having an 88% amino acid sequence identity and an already assigned biochemical role in the cell, the two subunits appear to have additional and distinctive cell functions. In particular, both subunits have been reported to be involved in tumor progression and metastasis. The aim of this study was to determine the specific, and potentially distinct, localizations of both subunits in tumor cells of different origin and differentiation and therefore to search for a possible link between their localization and the stage of disease. We used the GFP reporter system to analyze the ectopic expression of GFP-Nm23 proteins in head and neck tumor cell lines by fluorescent microscopy techniques. Our experiments revealed that GFP-fused Nm23-H1 and -H2 proteins display the same localization in transfected cells, regardless of their origin and differentiation status. The proteins are principally found in the cytosol and the endoplasmic reticulum. Moreover, some cells exhibit nuclear staining, which appears to be cell cycle-dependent.

Increased nm23 immunoreactivity is associated with selective inhibition of systemic tumour cell dissemination

AIMS

In vitro transfection experiments show that the nm23 gene suppresses metastasis, although the evidence from clinical studies is contradictory. The purpose of this study was to investigate whether nm23 selectively influences systemic, pleural, and lymphatic metastasis in non-small cell lung cancer (NSCLC).

METHODS

Forty two patients undergoing resection of NSCLC and lymph node sampling were enrolled prospectively. In each case, a bone marrow aspirate, pleural lavage, and lymph nodes were assessed using immunohistochemistry for epithelial antigens and morphology. The intensity of nm23-H1 immunoreactivity of the primary tumour was compared with the internal control of normal bronchial epithelium in 32 cases where available. The microvessel count (MVC) of each tumour was determined using immunohistochemistry for the endothelial cell marker CD34.

RESULTS

Tumour cell dissemination was detected in the bone marrow in 18 patients, in the pleura in seven, and in the lymph nodes in 21. Increased immunoreactivity for nm23 was found in the primary tumour in six patients, with none having tumour cells in the bone marrow, compared with 12 of 26 patients who showed nm23 immunoreactivity equal to or less than the control (Fisher's exact test: p = 0.043). This effect was confirmed to be independent of the MVC on multivariate analysis. There was no significant difference in the incidence of pleural or lymphatic tumour cell dissemination between the two groups.

CONCLUSION

nm23 appears to be a suppressor of systemic, but not lymphatic, metastasis in primary NSCLC.

Mutational analysis of the NM23.H1 gene in human breast cancer

NM23.H1 is a protein connected with tumor progression. Loss of heterozygosity and reduced expression of the gene have been associated with poor prognosis and increased incidence of metastases in many epithelial tumors. The aim of this study was to detect the presence of NM23.H1 point mutations or small deletions in human breast carcinomas by using the single-strand-conformation polymorphism (SSCP) technique. Mutational analysis was performed on 76 breast tumors, 10 of which had allelic deletion of the gene. The NM23.H1 mRNA content also was evaluated in each sample. Only a C-to-A transversion leading to a stop codon was found in the 5' untranslated region of exon 1. A polymorphic SSCP pattern was identified in exon 1; direct sequencing showed a C-to-T transition 30 nucleotides upstream from the 5' splice site flanking exon 1. None of the tumors analyzed presented both alleles inactivated. Our results suggest that NM23.H1 is rarely inactivated by point mutations.

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.

Frequent occurrence of loss of heterozygosity among tumor suppressor genes in uterine leiomyosarcoma

OBJECTIVE

Leiomyosarcoma of the uterus is a rare smooth muscle tumor; it is extremely malignant and the rates of local recurrence and metastasis are high. Since tumor suppressor genes are commonly altered in malignant tumors, it is possible that mutations in such genes are involved in the development of uterine leiomyosarcoma.

METHODS

Fifty-five patients (37-70 years of age) diagnosed as having smooth muscle tumors of the uterus were selected. DNA was extracted from four or five 8-microm-thick consecutive tissue sections of each smooth muscle tumor from the paraffin-embedded blocks. Loss of heterozygosity (LOH) was investigated at nine loci within or close to tumor suppressor genes (TP53, RB1, DCC, NM23, WT1, D14S267, P16, DPC4, PTCH).

RESULTS

Nineteen of twenty leiomyosarcomas revealed at least one instance of LOH among eight of the nine markers tested (one locus showed no LOH at all). In fact, 11 of the 20 cases exhibited two or more instances of LOH and, of the remaining 9 cases, 4 showed a point mutation of p53 in addition to an alteration in one of the 9 markers, while one exhibited a p53 mutation only.

CONCLUSION

An accumulation of genetic alterations among tumor suppressor genes may play a key role in the tumorigenesis and progression of uterine leiomyosarcoma.