Sponge non-metastatic Group I Nme gene/protein - structure and function is conserved from sponges to humans

The ancestral type of the R-RAS protein has oncogenic potential

BACKGROUND

The R-RAS2 is a small GTPase highly similar to classical RAS proteins at the regulatory and signaling levels. The high evolutionary conservation of R-RAS2, its links to basic cellular processes and its role in cancer, make R-RAS2 an interesting research topic. To elucidate the evolutionary history of R-RAS proteins, we investigated and compared structural and functional properties of ancestral type R-RAS protein with human R-RAS2.

METHODS

Bioinformatics analysis were used to elucidate the evolution of R-RAS proteins. Intrinsic GTPase activity of purified human and sponge proteins was analyzed with GTPase-GloTM Assay kit. The cell model consisted of human breast cancer cell lines MCF-7 and MDA-MB-231 transiently transfected with EsuRRAS2-like or HsaRRAS2. Biological characterization of R-RAS2 proteins was performed by Western blot on whole cell lysates or cell adhesion protein isolates, immunofluorescence and confocal microscopy, MTT test, colony formation assay, wound healing and Boyden chamber migration assays.

RESULTS

We found that the single sponge R-RAS2-like gene/protein probably reflects the properties of the ancestral R-RAS protein that existed prior to duplications during the transition to Bilateria, and to Vertebrata. Biochemical characterization of sponge and human R-RAS2 showed that they have the same intrinsic GTPase activity and RNA binding properties. By testing cell proliferation, migration and colony forming efficiency in MDA-MB-231 human breast cancer cells, we showed that the ancestral type of the R-RAS protein, sponge R-RAS2-like, enhances their oncogenic potential, similar to human R-RAS2. In addition, sponge and human R-RAS2 were not found in focal adhesions, but both homologs play a role in their regulation by increasing talin1 and vinculin.

CONCLUSIONS

This study suggests that the ancestor of all animals possessed an R-RAS2-like protein with oncogenic properties similar to evolutionarily more recent versions of the protein, even before the appearance of true tissue and the origin of tumors. Therefore, we have unraveled the evolutionary history of R-RAS2 in metazoans and improved our knowledge of R-RAS2 properties, including its structure, regulation and function.

Transfection of Sponge Cells and Intracellular Localization of Cancer-Related MYC, RRAS2, and DRG1 Proteins

The determination of the protein's intracellular localization is essential for understanding its biological function. Protein localization studies are mainly performed on primary and secondary vertebrate cell lines for which most protocols have been optimized. In spite of experimental difficulties, studies on invertebrate cells, including basal Metazoa, have greatly advanced. In recent years, the interest in studying human diseases from an evolutionary perspective has significantly increased. Sponges, placed at the base of the animal tree, are simple animals without true tissues and organs but with a complex genome containing many genes whose human homologs have been implicated in human diseases, including cancer. Therefore, sponges are an innovative model for elucidating the fundamental role of the proteins involved in cancer. In this study, we overexpressed human cancer-related proteins and their sponge homologs in human cancer cells, human fibroblasts, and sponge cells. We demonstrated that human and sponge MYC proteins localize in the nucleus, the RRAS2 in the plasma membrane, the membranes of the endolysosomal vesicles, and the DRG1 in the cell's cytosol. Despite the very low transfection efficiency of sponge cells, we observed an identical localization of human proteins and their sponge homologs, indicating their similar cellular functions.

Structure and function of cancer-related developmentally regulated GTP-binding protein 1 (DRG1) is conserved between sponges and humans

Cancer is a disease caused by errors within the multicellular system and it represents a major health issue in multicellular organisms. Although cancer research has advanced substantially, new approaches focusing on fundamental aspects of cancer origin and mechanisms of spreading are necessary. Comparative genomic studies have shown that most genes linked to human cancer emerged during the early evolution of Metazoa. Thus, basal animals without true tissues and organs, such as sponges (Porifera), might be an innovative model system for understanding the molecular mechanisms of proteins involved in cancer biology. One of these proteins is developmentally regulated GTP-binding protein 1 (DRG1), a GTPase stabilized by interaction with DRG family regulatory protein 1 (DFRP1). This study reveals a high evolutionary conservation of DRG1 gene/protein in metazoans. Our biochemical analysis and structural predictions show that both recombinant sponge and human DRG1 are predominantly monomers that form complexes with DFRP1 and bind non-specifically to RNA and DNA. We demonstrate the conservation of sponge and human DRG1 biological features, including intracellular localization and DRG1:DFRP1 binding, function of DRG1 in α-tubulin dynamics, and its role in cancer biology demonstrated by increased proliferation, migration and colonization in human cancer cells. These results suggest that the ancestor of all Metazoa already possessed DRG1 that is structurally and functionally similar to the human DRG1, even before the development of real tissues or tumors, indicating an important function of DRG1 in fundamental cellular pathways.

NME6 is a phosphotransfer-inactive, monomeric NME/NDPK family member and functions in complexes at the interface of mitochondrial inner membrane and matrix

Background

NME6 is a member of the nucleoside diphosphate kinase (NDPK/NME/Nm23) family which has key roles in nucleotide homeostasis, signal transduction, membrane remodeling and metastasis suppression. The well-studied NME1-NME4 proteins are hexameric and catalyze, via a phospho-histidine intermediate, the transfer of the terminal phosphate from (d)NTPs to (d)NDPs (NDP kinase) or proteins (protein histidine kinase). For the NME6, a gene/protein that emerged early in eukaryotic evolution, only scarce and partially inconsistent data are available. Here we aim to clarify and extend our knowledge on the human NME6.

Results

We show that NME6 is mostly expressed as a 186 amino acid protein, but that a second albeit much less abundant isoform exists. The recombinant NME6 remains monomeric, and does not assemble into homo-oligomers or hetero-oligomers with NME1-NME4. Consequently, NME6 is unable to catalyze phosphotransfer: it does not generate the phospho-histidine intermediate, and no NDPK activity can be detected. In cells, we could resolve and extend existing contradictory reports by localizing NME6 within mitochondria, largely associated with the mitochondrial inner membrane and matrix space. Overexpressing NME6 reduces ADP-stimulated mitochondrial respiration and complex III abundance, thus linking NME6 to dysfunctional oxidative phosphorylation. However, it did not alter mitochondrial membrane potential, mass, or network characteristics. Our screen for NME6 protein partners revealed its association with NME4 and OPA1, but a direct interaction was observed only with RCC1L, a protein involved in mitochondrial ribosome assembly and mitochondrial translation, and identified as essential for oxidative phosphorylation.

Conclusions

NME6, RCC1L and mitoribosomes localize together at the inner membrane/matrix space where NME6, in concert with RCC1L, may be involved in regulation of the mitochondrial translation of essential oxidative phosphorylation subunits. Our findings suggest new functions for NME6, independent of the classical phosphotransfer activity associated with NME proteins.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00707-0.

NME/NM23/NDPK and Histidine Phosphorylation

The NME (Non-metastatic) family members, also known as NDPKs (nucleoside diphosphate kinases), were originally identified and studied for their nucleoside diphosphate kinase activities. This family of kinases is extremely well conserved through evolution, being found in prokaryotes and eukaryotes, but also diverges enough to create a range of complexity, with homologous members having distinct functions in cells. In addition to nucleoside diphosphate kinase activity, some family members are reported to possess protein-histidine kinase activity, which, because of the lability of phosphohistidine, has been difficult to study due to the experimental challenges and lack of molecular tools. However, over the past few years, new methods to investigate this unstable modification and histidine kinase activity have been reported and scientific interest in this area is growing rapidly. This review presents a global overview of our current knowledge of the NME family and histidine phosphorylation, highlighting the underappreciated protein-histidine kinase activity of NME family members, specifically in human cells. In parallel, information about the structural and functional aspects of the NME family, and the knowns and unknowns of histidine kinase involvement in cell signaling are summarized.

A rare subpopulation of melanoma cells with low expression of metastasis suppressor NME1 is highly metastatic in vivo

Despite recent advances in melanoma treatment, metastasis and resistance to therapy remain serious clinical challenges. NME1 is a metastasis suppressor, a class of proteins which inhibits metastatic spread of cancer cells without impact on growth of the primary tumor. We have identified a rare subpopulation of cells with markedly reduced expression of NME1 (NME1LOW) in human melanoma cell lines. To enable isolation of viable NME1LOW cells for phenotypic analysis by fluorescence-activated cell sorting (FACS), a CRISPR-Cas9-mediated approach was used to attach an EGFP coding module to the C-terminus of the endogenous NME1 gene in melanoma cell lines. NME1LOW cells displayed enhanced collective invasion in vitro when implanted as 3D aggregates in Matrigel. NME1LOW cells were also highly metastatic to lung and liver when xenografted subcutaneously in immune-deficient NSG mice. RNA-seq analysis revealed that NME1LOW cells express elevated levels of genes associated with tumor aggressiveness, as well as with morphogenesis of tissues of neural crest-like origin (melanocytes and neurons, bone and heart tissues; GO: 0009653). The highly malignant NME1LOW variant of melanoma cells has potential to provide novel therapeutic targets and molecular markers for improved clinical management of patients with advanced melanoma.

Characterization of Nme5-Like Gene/Protein from the Red Alga Chondrus Crispus

The Nme gene/protein family of nucleoside diphosphate kinases (NDPK) was originally named after its member Nm23-H1/Nme1, the first identified metastasis suppressor. Human Nme proteins are divided in two groups. They all possess nucleoside diphosphate kinase domain (NDK). Group I (Nme1-Nme4) display a single type NDK domain, whereas Group II (Nme5-Nme9) display a single or several different NDK domains, associated or not associated with extra-domains. Data strongly suggest that, unlike Group I, none of the members of Group II display measurable NDPK activity, although some of them autophosphorylate. The multimeric form is required for the NDPK activity. Group I proteins are known to multimerize, while there are no data on the multimerization of Group II proteins. The Group II ancestral type protein was shown to be conserved in several species from three eukaryotic supergroups. Here, we analysed the Nme protein from an early branching eukaryotic lineage, the red alga Chondrus crispus. We show that the ancestral type protein, unlike its human homologue, was fully functional multimeric NDPK with high affinity to various types of DNA and dispersed localization throughout the eukaryotic cell. Its overexpression inhibits both cell proliferation and the anchorage-independent growth of cells in soft agar but fails to deregulate cell apoptosis. We conclude that the ancestral gene has changed during eukaryotic evolution, possibly in correlation with the protein function.

A survey of metastasis suppressors in Metazoa

Metastasis suppressors are genes/proteins involved in regulation of one or more steps of the metastatic cascade while having little or no effect on tumor growth. The list of putative metastasis suppressors is constantly increasing although thorough understanding of their biochemical mechanism(s) and evolutionary history is still lacking. Little is known about tumor-related genes in invertebrates, especially non-bilaterians and unicellular relatives of animals. However, in the last few years we have been witnessing a growing interest in this subject since it has been shown that many disease-related genes are already present in simple non-bilateral animals and even in their unicellular relatives. Studying human diseases using simpler organisms that may better represent the ancestral conditions in which the specific disease-related genes appeared could provide better understanding of how those genes function. This review represents a compilation of published literature and our bioinformatics analysis to gain a general insight into the evolutionary history of metastasis-suppressor genes in animals (Metazoa). Our survey suggests that metastasis-suppressor genes emerged in three different periods in the evolution of Metazoa: before the origin of metazoans, with the emergence of first animals and at the origin of vertebrates.

Characterization of a group I Nme protein of Capsaspora owczarzaki-a close unicellular relative of animals

Nucleoside diphosphate kinases are enzymes present in all domains of life. In animals, they are called Nme or Nm23 proteins, and are divided into group I and II. Human Nme1 was the first protein identified as a metastasis suppressor. Because of its medical importance, it has been extensively studied. In spite of the large research effort, the exact mechanism of metastasis suppression remains unclear. It is unknown which of the biochemical properties or biological functions are responsible for the antimetastatic role of the mammalian Nme1. Furthermore, it is not clear at which point in the evolution of life group I Nme proteins acquired the potential to suppress metastasis, a process that is usually associated with complex animals. In this study we performed a series of tests and assays on a group I Nme protein from filasterean Capsaspora owczarzaki, a close unicellular relative of animals. The aim was to compare the protein to the well-known human Nme1 and Nme2 homologs, as well as with the homolog from a simple animal-sponge (Porifera), in order to see how the proteins changed with the transition to multicellularity, and subsequently in the evolution of complex animals. We found that premetazoan-type protein is highly similar to the homologs from sponge and human, in terms of biochemical characteristics and potential biological functions. Like the human Nme1 and Nme2, it is able to diminish the migratory potential of human cancer cells in culture.

Nuclear functions of NME proteins

The NME family of proteins is composed of 10 isoforms, designated NME1-10, which are diverse in their enzymatic activities and patterns of subcellular localization. Each contains a conserved domain associated with a nucleoside diphosphate kinase (NDPK) function, although not all are catalytically active. Several of the NME isoforms (NME1, NME5, NME7, and NME8) also exhibit a 3'-5' exonuclease activity, suggesting roles in DNA proofreading and repair. NME1 and NME2 have been shown to translocate to the nucleus, although they lack a canonical nuclear localization signal. Binding of NME1 and NME2 to DNA does not appear to be sequence-specific in a strict sense, but instead is directed to single-stranded regions and/or other non-B-form structures. NME1 and NME2 have been identified as potential canonical transcription factors that regulate gene transcription through their DNA-binding activities. Indeed, the NME1 and NME2 isoforms have been shown to regulate gene expression programs in a number of cellular settings, and this regulatory function has been proposed to underlie their well-recognized ability to suppress the metastatic phenotype of cancer cells. Moreover, NME1 and, more recently, NME3, have been implicated in repair of both single- and double-stranded breaks in DNA. This suggests that reduced expression of NME proteins could contribute to the genomic instability that drives cancer progression. Clearly, a better understanding of the nuclear functions of NME1 and possibly other NME isoforms could provide critical insights into mechanisms underlying malignant progression in cancer. Indeed, clinical data indicate that the subcellular localization of NME1 may be an important prognostic marker in some cancers. This review summarizes putative functions of nuclear NME proteins in DNA binding, transcription, and DNA damage repair, and highlights their possible roles in cancer progression.

Histidine kinases and the missing phosphoproteome from prokaryotes to eukaryotes

Protein phosphorylation is the most common type of post-translational modification in eukaryotes. The phosphoproteome is defined as the complete set of experimentally detectable phosphorylation sites present in a cell's proteome under various conditions. However, we are still far from identifying all the phosphorylation sites in a cell mainly due to the lack of information about phosphorylation events involving residues other than Ser, Thr and Tyr. Four types of phosphate-protein linkage exist and these generate nine different phosphoresidues-pSer, pThr, pTyr, pHis, pLys, pArg, pAsp, pGlu and pCys. Most of the effort in studying protein phosphorylation has been focused on Ser, Thr and Tyr phosphorylation. The recent development of 1- and 3-pHis monoclonal antibodies promises to increase our understanding of His phosphorylation and the kinases and phosphatases involved. Several His kinases are well defined in prokaryotes, especially those involved in two-component system (TCS) signaling. However, in higher eukaryotes, NM23, a protein originally characterized as a nucleoside diphosphate kinase, is the only characterized protein-histidine kinase. This ubiquitous and conserved His kinase autophosphorylates its active site His, and transfers this phosphate either onto a nucleoside diphosphate or onto a protein His residue. Studies of NM23 protein targets using newly developed anti-pHis antibodies will surely help illuminate the elusive His phosphorylation-based signaling pathways. This review discusses the role that the NM23/NME/NDPK phosphotransferase has, how the addition of the pHis phosphoproteome will expand the phosphoproteome and make His phosphorylation part of the global phosphorylation world. It also summarizes why our understanding of phosphorylation is still largely restricted to the acid stable phosphoproteome, and highlights the study of NM23 histidine kinase as an entrée into the world of histidine phosphorylation.

Nuclear functions of NME proteins

The NME family of proteins is composed of 10 isoforms, designated NME1-10, which are diverse in their enzymatic activities and patterns of subcellular localization. Each contains a conserved domain associated with a nucleoside diphosphate kinase (NDPK) function, although not all are catalytically active. Several of the NME isoforms (NME1, NME5, NME7, and NME8) also exhibit a 3'-5' exonuclease activity, suggesting roles in DNA proofreading and repair. NME1 and NME2 have been shown to translocate to the nucleus, although they lack a canonical nuclear localization signal. Binding of NME1 and NME2 to DNA does not appear to be sequence-specific in a strict sense, but instead is directed to single-stranded regions and/or other non-B-form structures. NME1 and NME2 have been identified as potential canonical transcription factors that regulate gene transcription through their DNA-binding activities. Indeed, the NME1 and NME2 isoforms have been shown to regulate gene expression programs in a number of cellular settings, and this regulatory function has been proposed to underlie their well-recognized ability to suppress the metastatic phenotype of cancer cells. Moreover, NME1 and, more recently, NME3, have been implicated in repair of both single- and double-stranded breaks in DNA. This suggests that reduced expression of NME proteins could contribute to the genomic instability that drives cancer progression. Clearly, a better understanding of the nuclear functions of NME1 and possibly other NME isoforms could provide critical insights into mechanisms underlying malignant progression in cancer. Indeed, clinical data indicate that the subcellular localization of NME1 may be an important prognostic marker in some cancers. This review summarizes putative functions of nuclear NME proteins in DNA binding, transcription, and DNA damage repair, and highlights their possible roles in cancer progression.

Sponges: A Reservoir of Genes Implicated in Human Cancer

Recently, it was shown that the majority of genes linked to human diseases, such as cancer genes, evolved in two major evolutionary transitions—the emergence of unicellular organisms and the transition to multicellularity. Therefore, it has been widely accepted that the majority of disease-related genes has already been present in species distantly related to humans. An original way of studying human diseases relies on analyzing genes and proteins that cause a certain disease using model organisms that belong to the evolutionary level at which these genes have emerged. This kind of approach is supported by the simplicity of the genome/proteome, body plan, and physiology of such model organisms. It has been established for quite some time that sponges are an ideal model system for such studies, having a vast variety of genes known to be engaged in sophisticated processes and signalling pathways associated with higher animals. Sponges are considered to be the simplest multicellular animals and have changed little during evolution. Therefore, they provide an insight into the metazoan ancestor genome/proteome features. This review compiles current knowledge of cancer-related genes/proteins in marine sponges.

Functional and Structural Characterization of FAU Gene/Protein from Marine Sponge Suberites domuncula

Finkel-Biskis-Reilly murine sarcoma virus (FBR-MuSV) ubiquitously expressed (FAU) gene is down-regulated in human prostate, breast and ovarian cancers. Moreover, its dysregulation is associated with poor prognosis in breast cancer. Sponges (Porifera) are animals without tissues which branched off first from the common ancestor of all metazoans. A large majority of genes implicated in human cancers have their homologues in the sponge genome. Our study suggests that FAU gene from the sponge Suberites domuncula reflects characteristics of the FAU gene from the metazoan ancestor, which have changed only slightly during the course of animal evolution. We found pro-apoptotic activity of sponge FAU protein. The same as its human homologue, sponge FAU increases apoptosis in human HEK293T cells. This indicates that the biological functions of FAU, usually associated with "higher" metazoans, particularly in cancer etiology, possess a biochemical background established early in metazoan evolution. The ancestor of all animals possibly possessed FAU protein with the structure and function similar to evolutionarily more recent versions of the protein, even before the appearance of true tissues and the origin of tumors and metastasis. It provides an opportunity to use pre-bilaterian animals as a simpler model for studying complex interactions in human cancerogenesis.

Nme family of proteins--clues from simple animals

Nucleoside-diphosphate kinases (Nme/Nm23/NDPK) are evolutionarily conserved enzymes involved in many biological processes in vertebrates. The biochemical mechanisms of these processes are still largely unknown. The Nme family consists of ten members in humans of which Nme1/2 have been extensively studied in the context of carcinogenesis, especially metastasis formation. Lately, it has been proven that the majority of genes linked to human diseases were already present in species distantly related to humans. Most of cancer-related protein domains appeared during the two main evolutionary transitions-the emergence of unicellular eukaryotes and the transition to multicellular metazoans. In spite of these recent insights, current knowledge about cancer and status of cancer-related genes in simple animals is limited. One possible way of studying human diseases relies on analyzing genes/proteins that cause a certain disease by using model organism that represent the evolutionary level at which these genes have emerged. Therefore, basal metazoans are ideal model organisms for gaining a clearer picture how characteristics and functions of Nme genes changed in the transition to multicellularity and increasing complexity in animals, giving us exciting new evidence of their possible functions in potential pathological conditions in humans.

NDK-1, the homolog of NM23-H1/H2 regulates cell migration and apoptotic engulfment in C. elegans

Abnormal regulation of cell migration and altered rearrangement of cytoskeleton are characteristic of metastatic cells. The first described suppressor of metastatic processes is NM23-H1, which displays NDPK (nucleoside-diphosphate kinase) activity. To better understand the role of nm23 genes in cell migration, we investigated the function of NDK-1, the sole Caenorhabditis elegans homolog of group I NDPKs in distal tip cell (DTC) migration. Dorsal phase of DTC migration is regulated by integrin mediated signaling. We find that ndk-1 loss of function mutants show defects in this phase. Epistasis analysis using mutants of the α-integrin ina-1 and the downstream functioning motility-promoting signaling module (referred to as CED-10 pathway) placed NDK-1 downstream of CED-10/Rac. As DTC migration and engulfment of apoptotic corpses are analogous processes, both partially regulated by the CED-10 pathway, we investigated defects of apoptosis in ndk-1 mutants. Embryos and germ cells defective for NDK-1 showed an accumulation of apoptotic cell corpses. Furthermore, NDK-1::GFP is expressed in gonadal sheath cells, specialized cells for engulfment and clearence of apoptotic corpses in germ line, which indicates a role for NDK-1 in apoptotic corpse removal. In addition to the CED-10 pathway, engulfment in the worm is also mediated by the CED-1 pathway. abl-1/Abl and abi-1/Abi, which function in parallel to both CED-10/CED-1 pathways, also regulate engulfment and DTC migration. ndk-1(-);abi-1(-) double mutant embryos display an additive phenotype (e. g. enhanced number of apoptotic corpses) which suggests that ndk-1 acts in parallel to abi-1. Corpse number in ndk-1(-);ced-10(-) double mutants, however, is similar to ced-10(-) single mutants, suggesting that ndk-1 acts downstream of ced-10 during engulfment. In addition, NDK-1 shows a genetic interaction with DYN-1/dynamin, a downstream component of the CED-1 pathway. In summary, we propose that NDK-1/NDPK might represent a converging point of CED-10 and CED-1 pathways in the process of cytoskeleton rearrangement.

Structural and functional characterization of ribosomal protein gene introns in sponges

Ribosomal protein genes (RPGs) are a powerful tool for studying intron evolution. They exist in all three domains of life and are much conserved. Accumulating genomic data suggest that RPG introns in many organisms abound with non-protein-coding-RNAs (ncRNAs). These ancient ncRNAs are small nucleolar RNAs (snoRNAs) essential for ribosome assembly. They are also mobile genetic elements and therefore probably important in diversification and enrichment of transcriptomes through various mechanisms such as intron/exon gain/loss. snoRNAs in basal metazoans are poorly characterized. We examined 449 RPG introns, in total, from four demosponges: Amphimedon queenslandica, Suberites domuncula, Suberites ficus and Suberites pagurorum and showed that RPG introns from A. queenslandica share position conservancy and some structural similarity with "higher" metazoans. Moreover, our study indicates that mobile element insertions play an important role in the evolution of their size. In four sponges 51 snoRNAs were identified. The analysis showed discrepancies between the snoRNA pools of orthologous RPG introns between S. domuncula and A. queenslandica. Furthermore, these two sponges show as much conservancy of RPG intron positions between each other as between themselves and human. Sponges from the Suberites genus show consistency in RPG intron position conservation. However, significant differences in some of the orthologous RPG introns of closely related sponges were observed. This indicates that RPG introns are dynamic even on these shorter evolutionary time scales.

Characterization of Nme6-like gene/protein from marine sponge Suberites domuncula

Nucleoside diphosphate kinases (NDPKs) are evolutionarily conserved enzymes involved in many biological processes such as metastasis, proliferation, development, differentiation, ciliary functions, vesicle transport and apoptosis in vertebrates. Biochemical mechanisms of these processes are still largely unknown. Sponges (Porifera) are simple metazoans without tissues, closest to the common ancestor of all animals. They changed little during evolution and probably provide the best insight into the metazoan ancestors' genomic features. The purpose of this study was to address structural and functional properties of group II Nme6 gene/protein ortholog from the marine sponge Suberites domuncula, Nme6, in order to elucidate its evolutionary history. Sponge Nme6 gene and promoter were sequenced and analysed with various bioinformatical tools. Nme6 and Nme6Δ31 proteins were produced in E. coli strain BL21 and NDPK activity was measured using a coupled pyruvate kinase-lactate dehydrogenase assay. Subcellular localization in human tumour cells was examined by confocal scanning microscopy. Our results show that the sponge Nme6 compared to human Nme6 does not possess NDPK activity, does not localize in mitochondria at least in human cells although it has a putative mitochondrial signal sequence, lacks two recent introns that comprise miRNAs and have different transcriptional binding sites in the promoter region. Therefore, we conclude that the structure of Nme6 gene has changed during metazoan evolution possibly in correlation with the function of the protein.