Evidence for interaction between human PRUNE and nm23-H1 NDPKinase

Neuroimaging in PRUNE1 syndrome: a mini-review of the literature

Prune exopolyphosphatase 1 (PRUNE1) is a short-chain phosphatase that is part of the aspartic acid-histidine-histidine (DHH) family of proteins. PRUNE1 is highly expressed in the central nervous system and is crucially involved in neurodevelopment, cytoskeletal rearrangement, cell migration, and proliferation. Recently, biallelic PRUNE1 variants have been identified in patients with neurodevelopmental disorders, hypotonia, microcephaly, variable cerebral anomalies, and other features. PRUNE1 hypomorphic mutations mainly affect the DHH1 domain, leading to an impactful decrease in enzymatic activity with a loss-of-function mechanism. In this review, we explored both the clinical and radiological spectrum related to PRUNE1 pathogenic variants described to date. Specifically, we focused on neuroradiological findings that, together with clinical phenotypes and genetic data, allow us to best characterize affected children with diagnostic and potential prognostic implications.

Generation of Conditional Knockout Alleles for PRUNE-1

PRUNE1 is a member of the aspartic acid-histidine-histidine (DHH) protein superfamily, which could display an exopolyphosphatase activity and interact with multiple cellular proteins involved in the cytoskeletal rearrangement. It is widely expressed during embryonic development and is essential for embryogenesis. PRUNE1 could also be critical for postnatal development of the nervous system as it was found to be mutated in patients with microcephaly, brain malformations, and neurodegeneration. To determine the cellular function of PRUNE1 during development and in disease, we have generated conditional mouse alleles of the Prune1 in which loxP sites flank exon 6. Crossing these alleles with a ubiquitous Cre transgenic line resulted in a complete loss of PRUNE1 expression and embryonic defects identical to those previously described for Prune1 null embryos. In addition, breeding these alleles with a Purkinje cell-specific Cre line (Pcp2-Cre) resulted in the loss of Purkinje cells similar to that observed in patients carrying a mutation with loss of PRUNE1 function. Therefore, the Prune1 conditional mouse alleles generated in this study provide important genetic tools not only for dissecting the spatial and temporal roles of PRUNE1 during development but also for understanding the pathogenic role of PRUNE1 dysfunction in neurodegenerative or neurodevelopmental disease. In addition, from this work, we have described an approach that allows one to efficiently generate conditional mouse alleles based on mouse zygote electroporation.

PRUNE1 c.933G>A synonymous variant induces exon 7 skipping, disrupts the DHHA2 domain, and leads to an atypical NMIHBA syndrome presentation: Case report and review of the literature

Prune exopolyphosphatase-1 (PRUNE1) encodes a member of the aspartic acid-histidine-histidine (DHH) phosphodiesterase superfamily that regulates cell migration and proliferation during brain development. In 2015, biallelic PRUNE1 loss-of-function variants were identified to cause the neurodevelopmental disorder with microcephaly, hypotonia, and variable brain abnormalities (NMIHBA, OMIM#617481). NMIHBA is characterized by the namesake features and structural brain anomalies including thinning of the corpus callosum, cerebral and cerebellar atrophy, and delayed myelination. To date, 47 individuals have been reported in the literature, but the phenotypic spectrum of PRUNE1-related disorders and their causative variants remains to be characterized fully. Here, we report a novel homozygous PRUNE1 NM_021222.2:c.933G>A synonymous variant identified in a 6-year-old boy with intellectual and developmental disabilities, hypotonia, and spastic diplegia, but with the absence of microcephaly, brain anomalies, or seizures. Fibroblast RNA sequencing revealed that the PRUNE1 NM_021222.1:c.933G>A variant resulted in an in-frame skipping of the penultimate exon 7, removing 53 amino acids from an important protein domain. This case represents the first synonymous variant and the third pathogenic variant known to date affecting the DHH-associated domain (DHHA2 domain). These findings extend the genotypic and phenotypic spectrums in PRUNE1-related disorders and highlight the importance of considering synonymous splice site variants in atypical presentations.

Neurodevelopmental disorder with microcephaly, hypotonia, and variable brain anomalies in a consanguineous Iranian family is associated with a homozygous start loss variant in the PRUNE1 gene

Background

Homozygous or compound heterozygous PRUNE1 mutations cause a neurodevelopmental disorder with microcephaly, hypotonia, and variable brain malformations (NMIHBA) (OMIM #617481). The PRUNE1 gene encodes a member of the phosphoesterase (DHH) protein superfamily that is involved in the regulation of cell migration. To date, most of the described mutations in the PRUNE1 gene are clustered in DHH domain.

Methods

We subjected 4 members (two affected and two healthy) of a consanguineous Iranian family in the study. The proband underwent whole-exome sequencing and a start loss identified variant was confirmed by Sanger sequencing. Co-segregation of the detected variant with the disease in family was confirmed.

Results

By whole-exome sequencing, we identified the a start loss variant, NM_021222.3:c.3G>A; p.(Met1?), in the PRUNE1 in two patients of a consanguineous Iranian family with spastic quadriplegic cerebral palsy (CP), hypotonia, developmental regression, and cerebellar atrophy. Sanger sequencing confirmed the segregation of the variant with the disease in the family. Protein structure analysis also revealed that the variant probably leads to the deletion of DHH (Asp-His-His) domain, the active site of the protein, and loss of PRUNE1 function.

Conclusion

We identified a start loss variant, NM_021222.3:c.3G>A; p.(Met1?) in the PRUNE1 gene in two affected members as a possible cause of NMIHBA in an Iranian family. We believe that the study adds a new pathogenic variant in spectrum of mutations in the PRUNE1 gene as a cause of PRUNE1-related syndrome.

Functional Genomics of PRUNE1 in Neurodevelopmental Disorders (NDDs) Tied to Medulloblastoma (MB) and Other Tumors

We analyze the fundamental functions of Prune_1 in brain pathophysiology. We discuss the importance and maintenance of the function of Prune_1 and how its perturbation influences both brain pathological conditions, neurodevelopmental disorder with microcephaly, hypotonia, and variable brain anomalies (NMIHBA; OMIM: 617481), and tumorigenesis of medulloblastoma (MB) with functional correlations to other tumors. A therapeutic view underlying recent discoveries identified small molecules and cell penetrating peptides to impair the interaction of Prune_1 with protein partners (e.g., Nm23-H1), thus further impairing intracellular and extracellular signaling (i.e., canonical Wnt and TGF-β pathways). Identifying the mechanism of action of Prune_1 as responsible for neurodevelopmental disorders (NDDs), we have recognized other genes which are found overexpressed in brain tumors (e.g., MB) with functional implications in neurodevelopmental processes, as mainly linked to changes in mitotic cell cycle processes. Thus, with Prune_1 being a significant target in NDDs, we discuss how its network of action can be dysregulated during brain development, thus generating cancer and metastatic dissemination.

An identical-by-descent novel splice-donor variant in PRUNE1 causes a neurodevelopmental syndrome with prominent dystonia in two consanguineous Sudanese families

PRUNE1 is linked to a wide range of neurodevelopmental and neurodegenerative phenotypes. Multiple pathogenic missense and stop-gain PRUNE1 variants were identified in its DHH and DHHA2 phosphodiesterase domains. Conversely, a single splice alteration was previously reported. We investigated five patients from two unrelated consanguineous Sudanese families with an inherited severe neurodevelopmental disorder using whole-exome sequencing coupled with homozygosity mapping, segregation, and haplotype analysis. We identified a founder haplotype transmitting a homozygous canonical splice-donor variant (NM_021222.3:c.132+2T > C) in intron 2 of PRUNE1 segregated with the phenotype in all the patients. This splice variant possibly results in an in-frame deletion in the DHH domain or premature truncation of the protein. The phenotypes of the affected individuals showed phenotypic similarities characterized by remarkable pyramidal dysfunction and prominent extrapyramidal features (severe dystonia and bradykinesia). In conclusion, we identified a novel founder variant in PRUNE1 and corroborated abnormal splicing events as a disease mechanism in PRUNE1-related disorders. Given the phenotypes' consistency coupled with the founder effect, canonical and cryptic PRUNE1 splice-site variants should be carefully evaluated in patients presenting with prominent dystonia and pyramidal dysfunction.

Activation of Nm23-H1 to suppress breast cancer metastasis via redox regulation

Non-metastatic protein 23 H1 (Nm23-H1), a housekeeping enzyme, is a nucleoside diphosphate kinase-A (NDPK-A). It was the first identified metastasis suppressor protein. Nm23-H1 prolongs disease-free survival and is associated with a good prognosis in breast cancer patients. However, the molecular mechanisms underlying the role of Nm23-H1 in biological processes are still not well understood. This is a review of recent studies focusing on controlling NDPK activity based on the redox regulation of Nm23-H1, structural, and functional changes associated with the oxidation of cysteine residues, and the relationship between NDPK activity and cancer metastasis. Further understanding of the redox regulation of the NDPK function will likely provide a new perspective for developing new strategies for the activation of NDPK-A in suppressing cancer metastasis.

The multiple regulation of metastasis suppressor NM23-H1 in cancer

Metastasis is one of the leading causes of mortality in cancer patients. As the firstly identified metastasis suppressor, NM23-H1 has been endowed with expectation as a potent target in metastatic cancer therapy during the past decades. However, many challenges impede its clinical use. Accumulating evidence shows that NM23-H1 has a dichotomous role in tumor metastasis as a suppressor and promoter. It has potentially attributed to its versatile biochemical characteristics such as nucleoside diphosphate kinase (NDPK) activity, histidine kinase activity (HPK), exonuclease activity, and protein scaffold, which further augment the complexity and uncertainty of its physiological function. Simultaneously, tumor cells have evolved multiple ways to regulate the expression and function of NM23-H1 during tumorigenesis and metastasis. This review summarized and discussed the regulatory mechanisms of NM23-H1 in cancer including transcriptional activation, subcellular location, enzymatic activity, and protein degradation, which significantly modulate its anti-metastatic function.

Human Mpv17-like protein with a mitigating effect on mtDNA damage is involved in cAMP/PKA signaling in the mitochondrial matrix

Human Mpv17-like protein (M-LPH/Mpv17L) is thought to play a role in minimizing mitochondrial dysfunction caused by mitochondrial DNA (mtDNA) damage. We have recently demonstrated that, in addition to an increase of mtDNA damage, M-LPH-knockout (M-LPH-KO) in HepG2 cells causes a significant reduction of mitochondrial transcription factor A (TFAM) protein, an essential factor for mtDNA maintenance, along with an increase in its phosphorylation. These intracellular changes suggested an association of M-LPH with the cAMP/PKA signaling pathway, as selective degradation of TFAM by mitochondrial protease is driven by protein kinase A (PKA)-dependent phosphorylation. In the present study, we observed that M-LPH-KO in HepG2 cells caused an increase in the level of mitochondrial cAMP and a reduction of total cellular cyclic nucleotide phosphodiesterase (PDE) activity. In vitro-synthesized M-LPH showed PDE activity, which was inhibited by IBMX, a non-selective inhibitor of PDE. Furthermore, M-LPH-KO promoted PKA-dependent phosphorylation of some mitochondrial proteins. Taken together, the present findings suggest that M-LPH, which has structural features atypical of PDE family members, might be a novel human PDE involved in cAMP/PKA signaling in the mitochondrial matrix.

The Subcellular Localization and Oligomerization Preferences of NME1/NME2 upon Radiation-Induced DNA Damage

Nucleoside diphosphate kinases (NDPK/NME/Nm23) are enzymes composed of subunits NME1/NDPK A and NME2/NDPK B, responsible for the maintenance of the cellular (d)NTP pool and involved in other cellular processes, such as metastasis suppression and DNA damage repair. Although eukaryotic NDPKs are active only as hexamers, it is unclear whether other NME functions require the hexameric form, and how the isoenzyme composition varies in different cellular compartments. To examine the effect of DNA damage on intracellular localization of NME1 and NME2 and the composition of NME oligomers in the nucleus and the cytoplasm, we used live-cell imaging and the FRET/FLIM technique. We showed that exogenous NME1 and NME2 proteins co-localize in the cytoplasm of non-irradiated cells, and move simultaneously to the nucleus after gamma irradiation. The FRET/FLIM experiments imply that, after DNA damage, there is a slight shift in the homomer/heteromer balance between the nucleus and the cytoplasm. Collectively, our results indicate that, after irradiation, NME1 and NME2 engage in mutual functions in the nucleus, possibly performing specific functions in their homomeric states. Finally, we demonstrated that fluorophores fused to the N-termini of NME polypeptides produce the largest FRET effect and thus recommend this orientation for use in similar studies.

Altered MR imaging findings in a Japanese female child with PRUNE1-related disorder

Autosomal recessive PRUNE1 mutations on chromosome 1q21.3 are reported to cause a neurodevelopmental disorder with microcephaly, hypotonia, and variable brain malformations. Here, we report a Japanese case with a reported PRUNE1 mutation whose brain magnetic resonance imaging (MRI) showed specific imaging findings that have not been reported before. The patient was a 12-month-old girl, the first child of healthy and nonconsanguineous Japanese parents. She showed global developmental delay, intellectual disability, hypotonia, spastic quadriparesis, and hyperreflexia. Brain MRI showed cerebral and cerebellar atrophy, thin corpus callosum, white matter changes, and abnormal signal intensity of the brainstem, all of which were reported in the literature. In addition, we emphasize the three following imaging findings: a transient cerebral subcortical white matter lesion, atrophy of the midbrain and pontine tegmentum with a preserved pontine base, and abnormal signal intensity of the bilateral swelling putamina and medial portions of the thalami, which emerged after 4 years of age. The whole-exome sequencing (WES) analysis performed at the age of 4 years identified biallelic PRUNE1 variants, namely compound heterozygous mutations (c.[316G > A];[540 T > A],p.[Asp106Asn];[Cys180*]). Although the diagnosis of PRUNE1-related disorder requires WES, we think that these new characteristic MRI findings may help in the diagnosis of PRUNE1-related disorder.

A homozygous canonical splice acceptor site mutation in PRUNE1 is responsible for a rare childhood neurodegenerative disease in Manitoba Cree families

Autosomal recessive PRUNE1 mutations are reported to cause a severe neurodevelopmental disorder with microcephaly, hypotonia, and brain malformations. We describe clinical and neuropathological features in a cohort of nine individuals of Cree descent who, because of a founder effect, are homozygous for the same PRUNE1 mutation. They follow the course of a combined neuromuscular and neurodegenerative disease, rather than a pure failure of normal development. This cohort presented in infancy with features of lower motor neuron disease, such as hypotonia, contractures, tongue fasciculations, and feeding difficulties in the absence of congenital brain anomalies and microcephaly. A neurodegenerative course followed with onset of seizures, spasticity, and respiratory insufficiency. Muscle biopsies showed denervation/reinnervation features, nonspecific atrophy and end-stage atrophy. Autopsy findings in two patients are also described, suggesting length dependent central motor axon degeneration, peripheral motor axon degeneration, possible spinal motor neuron degeneration, and accumulation of beta amyloid precursor protein inclusions in select brainstem nuclei. Exome sequencing and homozygosity mapping identified a homozygous PRUNE1 mutation in a canonical splice site, which produces two abnormal PRUNE1 mRNA products. Based on our studies and the histopathology and phenotypic data, we provide further evidence that this disorder leads to a neurodegenerative disease affecting both the peripheral and central nervous systems and suggest that the pathogenic c.521-2A>G mutation could lead to an altered effect on tubulin dynamics.

A competitive cell-permeable peptide impairs Nme-1 (NDPK-A) and Prune-1 interaction: therapeutic applications in cancer

The understanding of protein-protein interactions is crucial in order to generate a second level of functional genomic analysis in human disease. Within a cellular microenvironment, protein-protein interactions generate new functions that can be defined by single or multiple modes of protein interactions. We outline here the clinical importance of targeting of the Nme-1 (NDPK-A)-Prune-1 protein complex in cancer, where an imbalance in the formation of this protein-protein complex can result in inhibition of tumor progression. We discuss here recent functional data using a small synthetic competitive cell-permeable peptide (CPP) that has shown therapeutic efficacy for impairing formation of the Nme-1-Prune-1 protein complex in mouse preclinical xenograft tumor models (e.g., breast, prostate, colon, and neuroblastoma). We thus believe that further discoveries in the near future related to the identification of new protein-protein interactions will have great impact on the development of new therapeutic strategies against various cancers.

The NDPK/NME superfamily: state of the art

Nucleoside diphosphate kinases (NDPK) are nucleotide metabolism enzymes encoded by NME genes (also called NM23). Given the fact that not all NME-encoded proteins are catalytically active NDPKs and that NM23 generally refers to clinical studies on metastasis, we use here NME/NDPK to denote the proteins. Since their discovery in the 1950's, NMEs/NDPKs have been shown to be involved in multiple physiological and pathological cellular processes, but the molecular mechanisms have not been fully determined. Recent progress in elucidating these underlying mechanisms has been presented by experts in the field at the 10th International Congress on the NDPK/NME/AWD protein family in October 2016 in Dubrovnik, Croatia, and is summarized in review articles or original research in this and an upcoming issue of Laboratory Investigation. Within this editorial, we discuss three major cellular processes that involve members of the multi-functional NME/NDPK family: (i) cancer and metastasis dissemination, (ii) membrane remodeling and nucleotide channeling, and iii) protein histidine phosphorylation.

NDPKA is not just a metastasis suppressor - be aware of its metastasis-promoting role in neuroblastoma

NDPK-A, encoded by nm23-H1 (also known as NME1) was the first metastasis suppressor discovered. Much of the attention has been focused on the metastasis-suppressing role of NDPK-A in human tumors, including breast carcinoma and melanoma. However, compelling evidence points to a metastasis-promoting role of NDPK-A in certain tumors such as neuroblastoma and lymphoma. To balance attention on this contrariety of NDPK-A in different cancer types, this review addresses the metastasis-promoting role of NDPK-A in neuroblastoma. Neuroblastoma is an embryonic tumor, arising from neural crest cells that fail to differentiate into the sympathetic nervous system. We summarize and discuss nm23-H1 genetics and the prognosis of neuroblastoma, structural and functional changes associated with the S120G mutation of NDPK-A, as well as the evidence supporting the role of NDPK-A as a metastasis promoter. Also discussed are the NDPK-A relevant molecular determinants of neuroblastoma metastasis, and metastasis-relevant neural crest development. Because of NDPK-A's dichotomous role in tumor metastasis as both a suppressor and a promoter, tumor genome/exome profiles are necessary to identify the molecular drivers of metastasis in the NDPK-A network for developing tumor-specific therapies.

PRUNE Syndrome Is a New Neurodevelopmental Disorder: Report and Review

PRUNE syndrome, or neurodevelopmental disorder with microcephaly, hypotonia, and variable brain anomalies (OMIM#617481), is a new rare autosomal recessive neurodevelopmental disease that is caused by homozygous or compound heterozygous mutation in PRUNE1 on chromosome 1q21. Here, We report on 12-month-old and 30-month-old girls from 2 unrelated Saudi families with typical presentations of PRUNE syndrome. Both patients had severe developmental delay, progressive microcephaly, and dysmorphic features. Brain magnetic resonance imaging showed slight thinning in the corpus callosum, mild frontal brain atrophy, and delayed myelination in one of the patients. Both patients had the same missense mutation in PRUNE1 (c.383G>A, p.Arg128Gln), which was not reported before in a homozygous state. We compared our patients to previously reported cases. In conclusion, We suggest that clinicians consider PRUNE syndrome in any child presenting with dysmorphic features, developmental delay, progressive microcephaly, central hypotonia, peripheral spasticity, delayed myelination, brain atrophy, and a thin corpus callosum.

Genes that Affect Brain Structure and Function Identified by Rare Variant Analyses of Mendelian Neurologic Disease

Development of the human nervous system involves complex interactions among fundamental cellular processes and requires a multitude of genes, many of which remain to be associated with human disease. We applied whole exome sequencing to 128 mostly consanguineous families with neurogenetic disorders that often included brain malformations. Rare variant analyses for both single nucleotide variant (SNV) and copy number variant (CNV) alleles allowed for identification of 45 novel variants in 43 known disease genes, 41 candidate genes, and CNVs in 10 families, with an overall potential molecular cause identified in >85% of families studied. Among the candidate genes identified, we found PRUNE, VARS, and DHX37 in multiple families and homozygous loss-of-function variants in AGBL2, SLC18A2, SMARCA1, UBQLN1, and CPLX1. Neuroimaging and in silico analysis of functional and expression proximity between candidate and known disease genes allowed for further understanding of genetic networks underlying specific types of brain malformations.

The cAMP phosphodiesterase Prune localizes to the mitochondrial matrix and promotes mtDNA replication by stabilizing TFAM

Compartmentalized cAMP signaling regulates mitochondrial dynamics, morphology, and oxidative phosphorylation. However, regulators of the mitochondrial cAMP pathway, and its broad impact on organelle function, remain to be explored. Here, we report that Drosophila Prune is a cyclic nucleotide phosphodiesterase that localizes to the mitochondrial matrix. Knocking down prune in cultured cells reduces mitochondrial transcription factor A (TFAM) and mitochondrial DNA (mtDNA) levels. Our data suggest that Prune stabilizes TFAM and promotes mitochondrial DNA (mtDNA) replication through downregulation of mitochondrial cAMP signaling. In addition, our work demonstrates the prevalence of mitochondrial cAMP signaling in metazoan and its new role in mitochondrial biogenesis.

Nucleoside diphosphate kinases (NDPKs) in animal development

In textbooks of biochemistry, nucleoside diphosphate conversion to a triphosphate by nucleoside diphosphate 'kinases' (NDPKs, also named NME or NM23 proteins) merits a few lines of text. Yet this essential metabolic function, mediated by a multimeric phosphotransferase protein, has effects that lie beyond a simple housekeeping role. NDPKs attracted more attention when NM23-H1 was identified as the first metastasis suppressor gene. In this review, we examine these NDPK enzymes from a developmental perspective because of the tractable phenotypes found in simple animal models that point to common themes. The data suggest that NDPK enzymes control the availability of surface receptors to regulate cell-sensing cues during cell migration. NDPKs regulate different forms of membrane enclosure that engulf dying cells during development. We suggest that NDPK enzymes have been essential for the regulated uptake of objects such as bacteria or micronutrients, and this evolutionarily conserved endocytic function contributes to their activity towards the regulation of metastasis.

Metastasis suppressors Nm23H1 and Nm23H2 differentially regulate neoplastic transformation and tumorigenesis

Nm23H1 and H2 are prototypical metastasis suppressors with diverse functions, but recent studies suggest that they may also regulate tumorigenesis. Here, we employed both cellular and in vivo assays to examine the effect of Nm23H1 and H2 on tumorigenesis induced by oncogenic Ras and/or p53 deficiency. Co-expression of Nm23H1 but not H2 in NIH3T3 cells effectively suppressed neoplastic transformation and tumorigenesis induced by the oncogenic H-Ras G12V mutant. Overexpression of Nm23H1 but not H2 also inhibited tumorigenesis by human cervical cancer HeLa cells with p53 deficiency. However, in human non-small-cell lung carcinoma H1299 cells harboring N-Ras Q61K oncogenic mutation and p53 deletion, overexpression of Nm23H1 did not affect tumorigenesis in nude mice assays, while overexpression of Nm23H2 enhanced tumor growth with elevated expression of the c-Myc proto-oncogene. Collectively, these results suggest that Nm23H1 and H2 have differential abilities to modulate tumorigenesis.

Janus-faces of NME-oncoprotein interactions

Since the identification of Nm23 (NME1, NME/NM23 nucleoside diphosphate kinase 1) as the first non-metastatic protein, a great deal of research on members of the NME family of proteins has focused on roles in processes implicated in carcinogenesis and particularly their regulation of cellular motility and the process of metastatic spread. To date, there are ten identified members of this family of genes, and these can be dichotomized into groups both taxonomically and by the presence or absence of their nucleoside diphosphate kinase activity with NMEs 1-4 encoding nucleoside diphosphate kinases (NDPKs) and NMEs 5-9 plus RP2 displaying little if any NDPK activity. NMEs are relatively small proteins that can form hetero-oligomers (typically hexamers), and given the apparent genetic redundancy of some NMEs and the number of different isoforms, it is perhaps not surprising that there remains a great deal of uncertainty regarding their function and even more regarding cellular mechanisms of action. Since residues that contribute to NDPK activity span much of the protein, it seems likely that the consequences of NME expression must be mediated through their NDPK activity, through interactions with other structures in cells including protein-protein interactions or through combinations of these. Our goal in this review is to focus on some of the protein-protein interactions that have been identified and to highlight some of the challenges that face this area of research.

A therapeutic approach to treat prostate cancer by targeting Nm23-H1/h-Prune interaction

Nm23-H1 is a metastasis suppressor gene whose overexpression is associated with both reduced cell motility in various cancers and increased metastatic potential in neuroblastomas, osteosarcomas, and hematological malignances. We previously reported that Nm23-H1 exerts tumor suppressor action in prostate cancer cells and that h-Prune, which is overexpressed in various tumor types, binds Nm23-H1. Moreover, blockage of the Nm23-H1/h-Prune interaction with a competitive permeable peptide (CPP) attenuates migration of breast and neuroblastoma cells. This series of events suggests that the Nm23-H1/h-Prune protein complex regulates cancer progression and that its specific impairment could be a new therapeutic strategy in oncology. We found that CPP leads to inhibition of the AKT/mTORv and NF-kBv signaling pathways and also activates apoptosis. To obtain a proof-of-concept of our hypothesis, we used a xenograft model of prostate cancer to evaluate whether impairment of this complex using CPP results in an anti-tumoral effect. Using a mouse orthotopic model with bioluminescent imaging, we show evidences that CPP reduces prostate cancer metastases formation. In conclusion, CPP being able to impair formation of the h-Prune/Nm23-H1 complex holds promise for the treatment of prostate cancer.

Neuroblastoma tumorigenesis is regulated through the Nm23-H1/h-Prune C-terminal interaction

Nm23-H1 is one of the most interesting candidate genes for a relevant role in Neuroblastoma pathogenesis. H-Prune is the most characterized Nm23-H1 binding partner, and its overexpression has been shown in different human cancers. Our study focuses on the role of the Nm23-H1/h-Prune protein complex in Neuroblastoma. Using NMR spectroscopy, we performed a conformational analysis of the h-Prune C-terminal to identify the amino acids involved in the interaction with Nm23-H1. We developed a competitive permeable peptide (CPP) to impair the formation of the Nm23-H1/h-Prune complex and demonstrated that CPP causes impairment of cell motility, substantial impairment of tumor growth and metastases formation. Meta-analysis performed on three Neuroblastoma cohorts showed Nm23-H1 as the gene highly associated to Neuroblastoma aggressiveness. We also identified two other proteins (PTPRA and TRIM22) with expression levels significantly affected by CPP. These data suggest a new avenue for potential clinical application of CPP in Neuroblastoma treatment.

Mapping functional interaction sites of human prune C-terminal domain by NMR spectroscopy in human cell lysates

Get well prune: The C-terminal third domain of h-prune is largely unfolded and involved in relevant protein-protein interactions, particularly with Nm23-H1 (see figure), GSK-3β and gelsolin. This study shows that protein functions mediated by protein-protein interactions can be accurately followed in cell lysates by using fast NMR spectroscopy, which could be easily used for a very efficient NMR drug-discovery strategy.

Insights into the biology and prevention of tumor metastasis provided by the Nm23 metastasis suppressor gene

Metastatic disease is the major cause of death among cancer patients. A class of genes, named metastasis suppressors, has been described to specifically regulate the metastatic process. The metastasis suppressor genes are downregulated in the metastatic lesion compared to the primary tumor. In this review, we describe the body of research surrounding the first metastasis suppressor identified, Nm23. Nm23 overexpression in aggressive cancer cell lines reduced their metastatic potential in vivo with no significant reduction in primary tumor size. A complex mechanism of anti-metastatic action is unfolding involving several known Nm23 enzymatic activities (nucleotide diphosphate kinase, histidine kinase, and 3'-5' exonuclease), protein-protein interactions, and downstream gene regulation properties. Translational approaches involving Nm23 have progressed to the clinic. The upregulation of Nm23 expression by medroxyprogesterone acetate has been tested in a phase II trial. Other approaches with significant preclinical success include gene therapy using traditional or nanoparticle delivery, and cell permeable Nm23 protein. Recently, based on the inverse correlation of Nm23 and LPA1 expression, a LPA1 inhibitor has been shown to both inhibit metastasis and induce metastatic dormancy.

Protein-protein interactions: a mechanism regulating the anti-metastatic properties of Nm23-H1

Nm23-H1, also known as NDPK-A, was the first of a class of metastasis suppressor genes to be identified. Overexpression of Nm23-H1 in metastatic cell lines (melanoma, breast carcinoma, prostate, colon, hepatocellular, and oral squamous cell carcinoma) reduced cell motility in in vitro assays and metastatic potential in xenograft models, without a significant effect on primary tumor size. The mechanism of Nm23-H1 suppression of metastasis, however, is incompletely understood. Nm23-H1 has been reported to bind proteins, including those in small G-protein complexes, transcriptional complexes, the Map kinase, the TGF-β signaling pathways and the cytoskeleton. Evidence supporting these associations is presented together with evidence of resultant biochemical and phenotypic consequences of association. Cumulatively, the data suggest that part of the anti-metastatic function of Nm23-H1 lies in pathways that it interrupts via binding and inactivation of proteins.

Functional modulation of the metastatic suppressor Nm23-H1 by oncogenic viruses

Evidence over the last two decades from a number of disciplines has solidified some fundamental concepts in metastasis, a major contributor to cancer associated deaths. However, significant advances have been made in controlling this critical cellular process by focusing on targeted therapy. A key set of factors associated with this invasive phenotype is the nm23 family of over twenty metastasis-associated genes. Among the eight known isoforms, Nm23-H1 is the most studied potential anti-metastatic factor associated with human cancers. Importantly, a growing body of work has clearly suggested a critical role for Nm23-H1 in limiting tumor cell motility and progression induced by several tumor viruses, including Epstein-Barr virus (EBV), Kaposi's sarcoma associated herpes virus (KSHV) and human papilloma virus (HPV). A more in depth understanding of the interactions between tumor viruses encoded antigens and Nm23-H1 will facilitate the elucidation of underlying mechanism(s) which contribute to virus-associated cancers. Here, we review recent studies to explore the molecular links between human oncogenic viruses and progression of metastasis, in particular the deregulation of Nm23-H1 mediated suppression.

Protein-protein interactions: a mechanism regulating the anti-metastatic properties of Nm23-H1

Nm23-H1, also known as NDPK-A, was the first of a class of metastasis suppressor genes to be identified. Overexpression of Nm23-H1 in metastatic cell lines (melanoma, breast carcinoma, prostate, colon, hepatocellular, and oral squamous cell carcinoma) reduced cell motility in in vitro assays and metastatic potential in xenograft models, without a significant effect on primary tumor size. The mechanism of Nm23-H1 suppression of metastasis, however, is incompletely understood. Nm23-H1 has been reported to bind proteins, including those in small G-protein complexes, transcriptional complexes, the Map kinase, the TGF-β signaling pathways and the cytoskeleton. Evidence supporting these associations is presented together with evidence of resultant biochemical and phenotypic consequences of association. Cumulatively, the data suggest that part of the anti-metastatic function of Nm23-H1 lies in pathways that it interrupts via binding and inactivation of proteins.

Developmental function of Nm23/awd: a mediator of endocytosis

The metastasis suppressor gene Nm23 is highly conserved from yeast to human, implicating a critical developmental function. Studies in cultured mammalian cells have identified several potential functions, but many have not been directly verified in vivo. Here, we summarize the studies on the Drosophila homolog of the Nm23 gene, named a bnormal w ing d iscs (awd), which shares 78% amino acid identity with the human Nm23-H1 and H2 isoforms. These studies confirmed that awd gene encodes a nucleoside diphosphate kinase, and provided strong evidence of a role for awd in regulating cell differentiation and motility via regulation of growth factor receptor signaling. The latter function is mainly mediated by control of endocytosis. This review provides a historical account of the discovery and subsequent analyses of the awd gene. We will also discuss the possible molecular function of the Awd protein that underlies the endocytic function.

The NM23 family in development

The NM23 (non-metastatic 23) family is almost universally conserved across all three domains of life: eubacteria, archaea and eucaryotes. Unicellular organisms possess one NM23 ortholog, whilst vertebrates possess several. Gene multiplication through evolution has been accompanied by structural and functional diversification. Many NM23 orthologs are nucleoside diphosphate kinases (NDP kinases), but some more recently evolved members lack NDP kinase activity and/or display other functions, for instance, acting as protein kinases or transcription factors. These members display overlapping but distinct expression patterns during vertebrate development. In this review, we describe the functional differences and similarities among various NM23 family members. Moreover, we establish orthologous relationships through a phylogenetic analysis of NM23 members across vertebrate species, including Xenopus laevis and zebrafish, primitive chordates and several phyla of invertebrates. Finally, we summarize the involvement of NM23 proteins in development, in particular neural development. Carcinogenesis is a process of misregulated development, and NM23 was initially implicated as a metastasis suppressor. A more detailed understanding of the evolution of the family and its role in vertebrate development will facilitate elucidation of the mechanism of NM23 involvement in human cancer.

The Nm23-H1-h-Prune complex in cellular physiology: a 'tip of the iceberg' protein network perspective

Nm23-H1 (also known as NDPKA) and h-Prune form a protein complex that is part of a little-understood protein network. Modifications of this complex correlate with cancer status. Here, we focus on the role of the Nm23-H1-h-Prune complex in cellular physiology, through an analysis of the balance between the 'bound' and 'non-bound' states of Nm23-H1 and h-Prune, whereby we speculate on the 'read-out' during cell homeostasis under non-balanced conditions. We have analysed the biochemical activities of both Nm23-H1 and h-Prune alone and in combination, focussing on the anti-metastatic activity of Nm23-H1. We have then investigated the cellular mechanisms responsible for the formation of the Nm23-H1-h-Prune complex. To evaluate the importance of the equilibrium between the formation of the Nm23-H1-h-Prune complex and the 'free' levels of Nm23-H1 and h-Prune, we propose a model based on a pro-cancer condition where this equilibrium is negatively affected.

The mammalian Nm23/NDPK family: from metastasis control to cilia movement

Nucleoside diphosphate kinases (NDPK) are encoded by the NME genes, also called NM23. They catalyze the transfer of gamma-phosphate from nucleoside triphosphates to nucleoside diphosphates by a ping-pong mechanism involving the formation of a high energy phospho-histidine intermediate [1, 2]. Besides their known functions in the control of intracellular nucleotide homeostasis, they are involved in multiple physiological and pathological cellular processes such as differentiation, development, metastastic dissemination or cilia functions. Over the past 15 years, ten human genes have been discovered encoding partial, full length, and/or tandemly repeated Nm23/NDPK domains, with or without N-or C-terminal extensions and/or additional domains. These genes encode proteins exhibiting different functions at various tissular and subcellular localizations. Most of these genes appear late in evolution with the emergence of the vertebrate lineage. This review summarizes the present knowledge on these multitalented proteins.

The mammalian Nm23/NDPK family: from metastasis control to cilia movement

Nucleoside diphosphate kinases (NDPK) are encoded by the NME genes, also called NM23. They catalyze the transfer of gamma-phosphate from nucleoside triphosphates to nucleoside diphosphates by a ping-pong mechanism involving the formation of a high energy phospho-histidine intermediate [1, 2]. Besides their known functions in the control of intracellular nucleotide homeostasis, they are involved in multiple physiological and pathological cellular processes such as differentiation, development, metastastic dissemination or cilia functions. Over the past 15 years, ten human genes have been discovered encoding partial, full length, and/or tandemly repeated Nm23/NDPK domains, with or without N-or C-terminal extensions and/or additional domains. These genes encode proteins exhibiting different functions at various tissular and subcellular localizations. Most of these genes appear late in evolution with the emergence of the vertebrate lineage. This review summarizes the present knowledge on these multitalented proteins.

Regulators affecting the metastasis suppressor activity of Nm23-H1

Nm23-H1 encodes nucleoside diphosphate kinase A (NDPK-A) and is known to have a metastasis suppressive activity in many tumor cells. However, it has many other functions as well. Recent studies have shown that the interacting proteins with Nm23-H1 which mediate the cell proliferation, may act as modulators of the metastasis suppressor activity. The interacting proteins with Nm23-H1 can be classified into 3 groups. The first group of proteins can be classified as upstream kinases of Nm23-H1 such as CKI and Aurora-A/STK15. The second group of proteins acts as downstream effectors for the regulation of specific gene transcriptions, GTP-binding protein functions, and signal transduction in Erk signal cascade. The third group of proteins can be classified as bi-directionally influencing binding partners of Nm23-H1. As a result, the interactions with Nm23-H1 and binding partners have implications in the biochemical characterization involved in metastasis and tumorigenesis.

Regulators affecting the metastasis suppressor activity of Nm23-H1

Nm23-H1 encodes nucleoside diphosphate kinase A (NDPK-A) and is known to have a metastasis suppressive activity in many tumor cells. However, it has many other functions as well. Recent studies have shown that the interacting proteins with Nm23-H1 which mediate the cell proliferation, may act as modulators of the metastasis suppressor activity. The interacting proteins with Nm23-H1 can be classified into 3 groups. The first group of proteins can be classified as upstream kinases of Nm23-H1 such as CKI and Aurora-A/STK15. The second group of proteins acts as downstream effectors for the regulation of specific gene transcriptions, GTP-binding protein functions, and signal transduction in Erk signal cascade. The third group of proteins can be classified as bi-directionally influencing binding partners of Nm23-H1. As a result, the interactions with Nm23-H1 and binding partners have implications in the biochemical characterization involved in metastasis and tumorigenesis.

Clinical-translational approaches to the Nm23-H1 metastasis suppressor

Nm23-H1 significantly reduces metastasis without effects on primary tumor size and was the first discovered metastasis suppressor gene. At least three mechanisms are thought to contribute to the metastasis-suppressive effect of Nm23-H1: (a) its histidine kinase activity toward ATP-citrate lyase, aldolase C, and the kinase suppressor of ras, with the last inactivating mitogen-activated protein kinase signaling; (b) binding proteins that titer out "free" Nm23-H1 and inhibit its ability to suppress metastasis; and (c) altered gene expression downstream of Nm23-H1, particularly an inverse association with the lysophosphatidic acid receptor endothelial differentiation gene-28 (EDG2). Most metastasis suppressor genes, including Nm23-H1, affect metastatic colonization, which is the outgrowth of tumor cells in distant locations; therefore, they are of high translational interest. A phase II trial is ongoing to test the hypothesis that a compound, high-dose medroxyprogesterone acetate (MPA), used as an unconventional gluocorticoid, will stimulate breast cancer cells to reexpress Nm23-H1 and limit subsequent metastatic colonization.

Williams-Beuren syndrome TRIM50 encodes an E3 ubiquitin ligase

Williams-Beuren syndrome (WBS) is a neurodevelopmental and multisystemic disease that results from hemizygosity of approximately 25 genes mapping to chromosomal region 7q11.23. We report here the preliminary description of eight novel genes mapping within the WBS critical region and/or its syntenic mouse region. Three of these genes, TRIM50, TRIM73 and TRIM74, belong to the TRIpartite motif gene family, members of which were shown to be associated to several human genetic diseases. We describe the preliminary functional characterization of these genes and show that Trim50 encodes an E3 ubiquitin ligase, opening the interesting hypothesis that the ubiquitin-mediated proteasome pathway might be involved in the WBS phenotype.

Domain mapping on the human metastasis regulator protein h-Prune reveals a C-terminal dimerization domain

The human orthologue of the Drosophila prune protein (h-Prune) is an interaction partner and regulator of the metastasis suppressor protein NM23-H1 (non-metastatic protein 23). Studies on a cellular breast-cancer model showed that inhibition of the cAMP-specific PDE (phosphodiesterase) activity of h-Prune lowered the incidence of metastasis formation, suggesting that inhibition of h-Prune could be a therapeutic approach towards metastatic tumours. H-Prune shows no sequence similarity with known mammalian PDEs, but instead appears to belong to the DHH (Asp-His-His) superfamily of phosphoesterases. In order to investigate the structure and molecular function of h-Prune, we expressed recombinant h-Prune in a bacterial system. Through sequence analysis and limited proteolysis, we identified domain boundaries and a potential coiled-coil region in a C-terminal cortexillin homology domain. We found that this C-terminal domain mediated h-Prune homodimerization, as well as its interaction with NM23-H1. The PDE catalytic domain of h-Prune was mapped to the N-terminus and shown to be active, even when present in a monomeric form. Our findings indicate that h-Prune is composed of two independent active sites and two interaction sites for the assembly of oligomeric signalling complexes.

Phosphorylation of nm23-H1 by CKI induces its complex formation with h-prune and promotes cell motility

The combination of an increase in the cAMP-phosphodiesterase activity of h-prune and its interaction with nm23-H1 have been shown to be key steps in the induction of cellular motility in breast cancer cells. Here we present the molecular mechanisms of this interaction. The region of the nm23-h-prune interaction lies between S120 and S125 of nm23, where missense mutants show impaired binding; this region has been highly conserved throughout evolution, and can undergo serine phosphorylation by casein kinase I. Thus, the casein kinase I delta-epsilon specific inhibitor IC261 impairs the formation of the nm23-h-prune complex, which translates 'in vitro' into inhibition of cellular motility in a breast cancer cellular model. A competitive permeable peptide containing the region for phosphorylation by casein kinase I impairs cellular motility to the same extent as IC261. The identification of these two modes of inhibition of formation of the nm23-H1-h-prune protein complex pave the way toward new challenges, including translational studies using IC261 or this competitive peptide 'in vivo' to inhibit cellular motility induced by nm23-H1-h-prune complex formation during progression of breast cancer.

h-Prune is an independent prognostic marker for survival in esophageal squamous cell carcinoma

BACKGROUND

The human homologue of Drosophila prune (PRUNE, which encodes h-prune) protein interacts with glycogen synthase kinase 3 and promotes cell motility. The aim of our study was to investigate the impact of immunohistochemically detected h-prune expression on the survival of patients with esophageal squamous cell carcinoma (ESCC).

METHODS

Immunohistochemical staining of h-prune was performed for 205 surgically resected specimens of ESCC.

RESULTS

In total, 43 (21%) of 205 ESCC cases were positive for h-prune. h-prune-positive ESCC cases showed a more-advanced T stage (P < 0.0001), N stage (P < 0.0001), and tumor stage (P < 0.0001) than h-prune-negative ESCC cases. In the group of 116 stage II and III ESCC cases, recurrence of ESCC was frequently found in h-prune-positive cases. In patients with lung recurrence, the tumors were more likely to be h-prune positive than h-prune negative. Univariate analysis revealed that T stage (P < 0.0001), N stage (P < 0.0001), tumor stage (P < 0.0001), and h-prune staining (P < 0.0001) were significant prognostic factors for survival. Multivariate analysis indicated that N stage (P = 0.0182) and h-prune staining (P < 0.0001) were independent predictors for survival.

CONCLUSIONS

These results indicate that immunostaining of h-prune is useful to identify patients at high risk for recurrence or poor prognosis associated with ESCC.

Increased expression of h-prune is associated with tumor progression and poor survival in gastric cancer

The human homolog of the Drosophila prune protein (from PRUNE, which encodes h-prune), which interacts with glycogen synthase kinase 3, promotes cellular motility. H-prune also interacts with nm23-H1, a suppressor of cancer metastasis. It has been reported that stimulation of cellular motility by h-prune is enhanced by its interaction with nm23-H1 in breast cancer cells. In the present study, we examined the expression of h-prune and nm23-H1 during tumor progression in gastric cancer (GC). PRUNE mRNA was overexpressed in 12 (32%) of 38 GC cases by quantitative reverse transcription-polymerase chain reaction. PRUNE mRNA levels correlated significantly with advanced T grade, N grade and tumor stage. Immunohistochemical analysis revealed that 43 (30%) of 143 GC cases were positive for h-prune, and h-prune-positive GC cases showed more advanced T grade, N grade and tumor stage than h-prune-negative GC cases. One hundred and twenty-four (87%) of 143 GC cases were positive for nm23-H1, and nm23-H1 was expressed in almost all (42 cases, 98%) h-prune-positive GC cases. Many GC cases positive for both h-prune and nm23-H1 showed more advanced T grade, N grade and tumor stage than other type GC cases. Patients with h-prune-positive GC had a significantly worse survival rate than patients with h-prune-negative GC. These findings indicate that overexpression of h-prune is associated with tumor progression and aggressiveness of GC. nm23-H1 may enhance motility of cancer cells by interacting with h-prune.

The Suppressor of Killer of prune, a unique glutathione S-transferase

The prune-Killer of prune conditional dominant, lethal interaction in Drosophila was identified in the 1950s, but its mechanism remains unknown. We undertook a genetic screen for suppressors of this lethal interaction and identified a gene we named, Suppressor of Killer of prune Su(Kpn). Su(Kpn) is a unique protein with four N-terminal FLYWCH zinc-finger domains, an acidic domain and a C-terminal glutathione S-transferase (GST) domain. The GST domain of Su(Kpn) is of particular interest because GSTs are usually independent of other protein domains. While GSTs are generally thought of as detoxifying enzymes, they are also associated with cellular toxicity. We predict that the GST domain of the Su(Kpn) creates a toxic product in prune-Killer of prune flies that is lethal. The substrate of the Su(Kpn) remains unknown.

H-prune-nm23-H1 protein complex and correlation to pathways in cancer metastasis

Cancer is a multi-step process, one of the latest events correspond to metastasis formation and dissemination, to date the major cause of deaths. The h-prune-nm23-H1 protein complex and its activation of PDE-cAMP activity have been shown to correlate with breast cancer progression and metastasis formation. Here, we describe the protein complex formation and its involvement in cell migration. By gene expression studies and protein-protein pull-down analyses coupled to mass spectrometry we have identified new genes and pathways along which the h-prune-nm23-H1 complex exerts its function. We review here h-prune binding to the glycogen synthase kinase (GSK-3beta) and identify a new h-prune protein partner, Gelsolin, an ATP severing protein acting in focal adhesions, in a MDA-435 breast cancer cellular model. The results presented here underline the importance of this protein complex leading to new translational studies involved into the inhibition of cell migration, thus enhancing the potential of using this knowledge to direct inhibition of metastases formation in humans.