(1/5) The human nm23-H4 gene product is a mitochondrial nucleoside diphosphate kinase.
We demonstrate here the catalytic activity and subcellular localization of the Nm23-H4 protein, product of nm23-H4, a new member of the human nm23/nucleoside diphosphate (NDP) kinase gene family (Milon, L., Rousseau-Merck, M., Munier, A., Erent, M., Lascu, I., Capeau, J., and Lacombe, M. L. (1997) Hum. Genet. 99, 550-557). Nm3-H4 was synthesized in escherichia coli as the full-length protein and as a truncated form missing the N-terminal extension characteristic of mitochondrial targeting. The truncated form possesses NDP kinase activity, whereas the full-length protein is inactive, suggesting that the extension prevents enzyme folding and/or activity. X-ray crystallographic analysis was performed on active truncated Nm23-H4. Like other eukaryotic NDP kinases, it is a hexamer. Nm23-H4 naturally possesses a serine residue at position 129, equivalent to the K-pn mutation of the Drosophila NDP kinase. The x-ray structure shows that the presence of Ser(129) has local structural effects that weaken subunit interactions. Site-directed mutagenesis shows that the serine is responsible for the lability of Nm23-H4 to heat and urea treatment, because the S129P mutant is greatly stabilized. Examination of human embryonic kidney 293 cells transfected with green fluorescent protein fusions by confocal microscopy shows a specific mitochondrial localization of Nm23-H4 that was also demonstrated by Western blot analysis of subcellular fractions of these cells. Import into mitochondria is accompanied by cleavage of the N-terminal extension that results in NDP kinase activity. Submitochondrial fractionation indicates that Nm23-H4 is associated with mitochondrial membranes, possibly to the contact sites between the outer and inner membranes. (+info)
(2/5) 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. (+info)
(3/5) Decreased n-6/n-3 fatty acid ratio reduces the invasive potential of human lung cancer cells by downregulation of cell adhesion/invasion-related genes.
Recent studies have shown opposing effects of n-6 and n-3 fatty acids on the development of cancer and suggest a role for the ratio of n-6 to n-3 fatty acids in the control of cancer. However, whether an alteration in the n-6/n-3 fatty acid ratio of cancer cells affects their invasive potential has not been well investigated. We recently developed a genetic approach to modify the n-6/n-3 ratio by expression of the Caenorhabditis elegans fat-1 gene encoding an n-3 desaturase that converts n-6 to n-3 fatty acids in mammalian cells. The objective of this study was to examine the effect of alteration in the n-6/n-3 fatty acid ratio on the invasive potential of human lung cancer A549 cells. Adenovirus-mediated gene transfer of the n-3 desaturase resulted in a marked reduction of the n-6/n-3 fatty acid ratio, particularly the ratio of arachidonic acid to eicosapentaenic acid. Cell adhesion assay showed that the cells expressing fat-1 gene had a delayed adhesion and retarded colonization. Matrigel assay for invasion potential indicated a 2-fold reduction of cell migration in the fat-1 transgenic cells when compared with the control cells. An increased apoptosis was also observed in the fat-1 transgenic cells. Microarray and quantitative polymerase chain reaction revealed a downregulation of several adhesion/invasion-related genes (MMP-1, integrin-alpha2 and nm23-H4) in the fat-1 transgenic cells. These results demonstrate that a decreased n-6/n-3 fatty acid ratio reduces the invasion potential of human lung cancer cells by probably downregulating the cell adhesion/invasion-related molecules, suggesting a role for the ratio of n-6 to n-3 fatty acids in the prevention and treatment of cancer. (+info)
(4/5) New insights into lipid-Nucleoside Diphosphate Kinase-D interaction mechanism: protein structural changes and membrane reorganisation.
(5/5) Dual function of mitochondrial Nm23-H4 protein in phosphotransfer and intermembrane lipid transfer: a cardiolipin-dependent switch.