Nm23-H1 regulates the proliferation and differentiation of the human chronic myeloid leukemia K562 cell line: a functional proteomics study

Antitumor Activity and Potential Mechanism of Novel Fullerene Derivative Nanoparticles

The development of novel nanoparticles as a new generation therapeutic drug platform is an active field of chemistry and cancer research. In recent years, fullerene nanoparticles have received extensive attention due to their unique physical and chemical properties. Properly modified fullerene nanoparticles have excellent biocompatibility and significant anti-tumor activity, which makes them have broad application prospects in the field of cancer therapy. Therefore, understanding the anti-tumor mechanism of fullerene nanoparticles is of great significance for the design and development of anti-tumor drugs with low toxicity and high targeting. This review has focused on various anti-tumor mechanisms of fullerene derivatives and discusses their toxicity and their distribution in organisms. Finally, the review points out some urgent problems that need solution before fullerene derivatives as a new generation of anti-tumor nano-drug platform enter clinical research.

Lipid transfer proteins and instructive regulation of lipid kinase activities: Implications for inositol lipid signaling and disease

Cellular membranes are critical platforms for intracellular signaling that involve complex interfaces between lipids and proteins, and a web of interactions between a multitude of lipid metabolic pathways. Membrane lipids impart structural and functional information in this regulatory circuit that encompass biophysical parameters such as membrane thickness and fluidity, as well as chaperoning the interactions of protein binding partners. Phosphatidylinositol and its phosphorylated derivatives, the phosphoinositides, play key roles in intracellular membrane signaling, and these involvements are translated into an impressively diverse set of biological outcomes. The phosphatidylinositol transfer proteins (PITPs) are key regulators of phosphoinositide signaling. Found in a diverse array of organisms from plants, yeast and apicomplexan parasites to mammals, PITPs were initially proposed to be simple transporters of lipids between intracellular membranes. It now appears increasingly unlikely that the soluble versions of these proteins perform such functions within the cell. Rather, these serve to facilitate the activity of intrinsically biologically insufficient inositol lipid kinases and, in so doing, promote diversification of the biological outcomes of phosphoinositide signaling. The central engine for execution of such functions is the lipid exchange cycle that is a fundamental property of PITPs. How PITPs execute lipid exchange remains very poorly understood. Molecular dynamics simulation approaches are now providing the first atomistic insights into how PITPs, and potentially other lipid-exchange/transfer proteins, operate.

Sequenced Combinations of Cisplatin and Selected Phytochemicals towards Overcoming Drug Resistance in Ovarian Tumour Models

In the present study, cisplatin, artemisinin, and oleanolic acid were evaluated alone, and in combination, on human ovarian A2780, A2780^ZD0473R, and A2780^cisR cancer cell lines, with the aim of overcoming cisplatin resistance and side effects. Cytotoxicity was assessed by MTT reduction assay. Combination index (CI) values were used as a measure of combined drug effect. MALDI TOF/TOF MS/MS and 2-DE gel electrophoresis were used to identify protein biomarkers in ovarian cancer and to evaluate combination effects. Synergism from combinations was dependent on concentration and sequence of administration. Generally, bolus was most synergistic. Moreover, 49 proteins differently expressed by 2 ≥ fold were: CYPA, EIF5A1, Op18, p18, LDHB, P4HB, HSP7C, GRP94, ERp57, mortalin, IMMT, CLIC1, NM23, PSA3,1433Z, and HSP90B were down-regulated, whereas hnRNPA1, hnRNPA2/B1, EF2, GOT1, EF1A1, VIME, BIP, ATP5H, APG2, VINC, KPYM, RAN, PSA7, TPI, PGK1, ACTG and VDAC1 were up-regulated, while TCPA, TCPH, TCPB, PRDX6, EF1G, ATPA, ENOA, PRDX1, MCM7, GBLP, PSAT, Hop, EFTU, PGAM1, SERA and CAH2 were not-expressed in A2780^cisR cells. The proteins were found to play critical roles in cell cycle regulation, metabolism, and biosynthetic processes and drug resistance and detoxification. Results indicate that appropriately sequenced combinations of cisplatin with artemisinin (ART) and oleanolic acid (OA) may provide a means to reduce side effects and circumvent platinum resistance.

Low-Density Lipoproteins, High-Density Lipoproteins (HDL), and HDL-Associated Proteins Differentially Modulate Chronic Myelogenous Leukemia Cell Viability

Cellular lipid metabolism, lipoprotein interactions, and liver X receptor (LXR) activation have been implicated in the pathophysiology and treatment of cancer, although findings vary across cancer models and by lipoprotein profiles. In this study, we investigated the effects of human-derived low-density lipoproteins (LDL), high-density lipoproteins (HDL), and HDL-associated proteins apolipoprotein A1 (apoA1) and serum amyloid A (SAA) on markers of viability, cholesterol flux, and differentiation in K562 cells-a bone marrow-derived, stem-like erythroleukemia cell model of chronic myelogenous leukemia (CML). We further evaluated whether lipoprotein-mediated effects were altered by concomitant LXR activation. We observed that LDL promoted higher K562 cell viability in a dose- and time-dependent manner and increased cellular cholesterol concentrations, while LXR activation by the agonist TO901317 ablated these effects. LXR activation in the presence of HDL, apoA1 and SAA-rich HDL suppressed K562 cell viability, while robustly inducing mRNA expression of ATP-binding cassette transporter A1 (ABCA1). HDL and its associated proteins additionally suppressed mRNA expression of anti-apoptotic B-cell lymphoma-extra large (BCL-xL), and the erythroid lineage marker 5'-aminolevulinate synthase 2 (ALAS2), while SAA-rich HDL induced mRNA expression of the megakaryocytic lineage marker integrin subunit alpha 2b (ITGA2B). Together, these findings suggest that lipoproteins and LXR may impact the viability and characteristics of CML cells.

Upregulation of NM23-E2 accelerates the liver regeneration after 40% decreased-size liver transplantation in rats

BACKGROUND

Potential of liver regeneration after living-donor liver transplantation is closely associated with the recipient's prognosis, whereas exogenous gene might regulate the liver regeneration progress. NM23 is a multifunctional gene, which inhibits tumor metastasis and regulates cell proliferation, differentiation, development, and apoptosis; however, there is little research about NM23 in promoting liver cell proliferation.

METHODS

To investigate the effect of NM23-E2 on the liver cell proliferation, the NM23-E2 overexpression vector or negative control vector was transfected into BRL-3A cells and donor liver, respectively. NM23-E2, Cyclin D1, and PCNA expression levels in BRL-3A cells and liver tissues were detected by quantitative real-time polymerase chain reaction and Western blot analysis. Cell Counting Kit-8 was used to detect cell proliferation and flow cytometry for investigating cell cycle. The liver regeneration rate was determined by calculating (regenerated-liver weight of recipient - liver weight of donor/liver weight of donor) × 100%.

RESULTS

NM23-E2 overexpression increased the NM23-E2, Cyclin D1, and PCNA levels significantly in BRL-3A cells and liver tissues (P < 0.05). The number of S phase cells was more than that of negative control group, and cell proliferation rate was higher than that of the control group in BRL-3A cells markedly (P < 0.05). Moreover, the liver regeneration rate in the NM23-E2 overexpression group was also higher than that in negative control group on postoperative day 1, day 3, day 5, and day 7.

CONCLUSIONS

Overexpression of NM23-E2 can increase Cyclin D1 and PCNA expression, shorten cell cycle, and thereby promoting the proliferation of liver cells and accelerating the regeneration of liver after 40% decreased-size rat liver transplantation.

Nm23H1 mediates tumor invasion in esophageal squamous cell carcinoma by regulation of CLDN1 through the AKT signaling

Esophageal cancer is a lethal malignancy worldwide. Previously, low expression of metastasis suppressor Nm23H1 and tight junction (TJ) protein claudin-1 (CLDN1) have been known to correlate with poor prognosis in esophageal squamous cell carcinoma (ESCC). However, the molecular interaction between them has not been clarified. In the present study, we first examined the expression of Nm23H1 and CLDN1 in 74 surgical ESCC samples by immunohistochemistry (IHC) to verify their clinicopathologic significance. The biologic effects of Nm23H1 gene silencing or overexpression in ESCC cell lines were then studied by migration and invasion studies, and its regulation on CLDN1 expression was also investigated by western blot analysis. Moreover, the expression of Nm23H1 and CLDN1 at the same invasion front of ESCC tumors was verified by immunofluorescence. The results showed a significantly positive correlation between the expression of Nm23H1 and CLDN1 (γ=0.296, P=0.011) in surgical specimens, especially for the 34 tumors with lymph-node metastasis (γ=0.455, P=0.007). In ESCC cell lines, silencing of Nm23H1 expression markedly enhanced cell invasiveness, accompanied by increased Akt phosphorylation and decreased CLDN1 expression. Conversely, Nm23H1-expressed transfectants exhibited reduced invasiveness, decreased Akt phosphorylation and correspondingly increased CLDN1 expression. Regain of CLDN1 expression in ESCC cells significantly suppressed invasiveness, but did not influence the Akt phosphorylation. Moreover, treating Nm23H1-depleted cells with the AKT inhibitor MK2206 recovered CLDN1 expression, and diminished the invasiveness of ESCC cells. Finally, decreased expressions of both CLDN1 and E-cadherin were observed at the invasive front of the Nm23H1-negative tumors. Overall, our current study documented that reduced Nm23H1 expression activates the AKT signaling pathway, results in diminished CLDN1 expression and potentiates invasiveness of ESCC cells. Enhancement of Nm23H1 expression, inhibition of the AKT signaling pathway, or combined, might be a potential treatment strategy in selective ESCC patients.

From the Biology of PP2A to the PADs for Therapy of Hematologic Malignancies

Over the past decades, an emerging role of phosphatases in the pathogenesis of hematologic malignancies and solid tumors has been established. The tumor-suppressor protein phosphatase 2A (PP2A) belongs to the serine-threonine phosphatases family and accounts for the majority of serine-threonine phosphatase activity in eukaryotic cells. Numerous studies have shown that inhibition of PP2A expression and/or function may contribute to leukemogenesis in several hematological malignancies. Likewise, overexpression or aberrant expression of physiologic PP2A inhibitory molecules (e.g., SET and its associated SETBP1 and CIP2A) may turn off PP2A function and participate to leukemic progression. The discovery of PP2A as tumor suppressor has prompted the evaluation of the safety and the efficacy of new compounds, which can restore PP2A activity in leukemic cells. Although further studies are needed to better understand how PP2A acts in the intricate phosphatases/kinases cancer network, the results reviewed herein strongly support the development on new PP2A-activating drugs and the immediate introduction of those available into clinical protocols for leukemia patients refractory or resistant to current available therapies.

Micro-scale strategy to detect spermine and spermidine by MALDI-TOF MS in foods and identification of apoptosis-related proteins by nano-flow UPLC-MS/MS after treatment with spermine and spermidine

Spermine and spermidine are multiple-nitrogen compounds found in many foods. Both compounds are essential for cell growth and human health. This study established a simple and fast method of detecting spermine and spermidine in food samples by matrix-assisted laser desorption/ionization combined with time-of-flight mass spectrometry (MALDI-TOF MS). After a simple sample preparation procedure, spermine and spermidine were directly detected by MALDI-TOF MS with no additional purification procedure. The calibration curves for spermine and spermidine ranged from 0.1 to 10 μg/mL. In intra- and inter-batch assays of three different concentrations of spermine and spermidine, all relative standard deviations and relative errors were below 18.9%. These experimental results confirmed the practicability and effectiveness of the proposed MALDI-TOF MS method for fast determination of spermine and spermidine in food samples. Furthermore, since spermine and spermidine have important roles in apoptosis, up-regulation and down-regulation of spermine and spermidine during apoptosis were analyzed. After treating NRK-52E cells with spermine and spermidine, the cells were lysed, and cell proteins were collected, and digested. Apoptosis-related proteins were then identified by tandem MS.

Regulation of the metastasis suppressor Nm23-H1 by tumor viruses

Metastasis is the most common cause of cancer mortality. To increase the survival of patients, it is necessary to develop more effective methods for treating as well as preventing metastatic diseases. Recent advancement of knowledge in cancer metastasis provides the basis for development of targeted molecular therapeutics aimed at the tumor cell or its interaction with the host microenvironment. Metastasis suppressor genes (MSGs) are promising targets for inhibition of the metastasis process. During the past decade, functional significance of these genes, their regulatory pathways, and related downstream effector molecules have become a major focus of cancer research. Nm23-H1, first in the family of Nm23 human homologues, is a well-characterized, anti-metastatic factor linked with a large number of human malignancies. Mounting evidence to date suggests an important role for Nm23-H1 in reducing virus-induced tumor cell motility and migration. A detailed understanding of the molecular association between oncogenic viral antigens with Nm23-H1 may reveal the underlying mechanisms for tumor virus-associated malignancies. In this review, we will focus on the recent advances to our understanding of the molecular basis of oncogenic virus-induced progression of tumor metastasis by deregulation of Nm23-H1.

Inhibition of nm23-H1 gene expression in chronic myelogenous leukemia cells

For solid tumors of a malignant origin, the expression of the nm23-H1 gene is a positive prognostic factor. However, for chronic myeloid leukemia (CML), the prognostic role of nm23-H1 gene expression is unknown. The present study investigated the impact of nm23-H1 gene expression on the proliferation and migration of the CML K562 cell line to elucidate the association between nm23-H1 gene expression and CML cell survival. An RNAi lipo-recombinant plasmid of the nm23-H1 gene (pGCsi-nm23-H1) was constructed and transfected into the K562 cells. RT-PCR and western blotting were used to detect nm23-H1 mRNA and protein expression, respectively. The anchorage-independent growth ability of the transfected cells was observed in soft agar culture and the ability of the K562 cells to migrate was determined using a Transwell assay. Following the successful construction and transfection of the pGCsi-nm23-H1 plasmid into the K562 cells, nm23-H1 mRNA and protein expression levels were significantly lower compared with the control group. The stably-transfected pGCsi-nm23-H1 K562 cells exhibited a markedly increased ability to form colonies and the number and sizes of the colonies were significantly increased compared with those of the control. In vitro, the cells migrated through a Matrigel-coated membrane during incubation for 20 h. The Transwell assay revealed that the quantitative number of pGCsi-nm23-H1 K562 cells that migrated into the lower compartment of the invasion chamber was markedly increased compared with the control. In conclusion, nm23-H1 gene expression may inhibit K562 cell proliferation and migration. nm23-H1 may be a cancer suppressor gene and play a significant role in inhibiting the survival of CML cells.

Nm23-H1 protein binds to APE1 at AP sites and stimulates AP endonuclease activity following ionizing radiation of the human lung cancer A549 cells

Non-metastatic protein-23 homolog-1 (Nm23-H1) is a multifunctional protein with DNase and histidine protein kinase activities. Human apurinic endonuclease-1 (APE1) is the AP endonuclease DNA base excision repair (BER) enzyme involved in several important cellular functions. Since the relationship between Nm23-H1 and APE1 proteins is unclear, we evaluated their interaction at different time points after irradiating human lung cancer A549 cells with X-rays. We found that Nm23-H1 and APE1 overexpression was induced by irradiation in a dose- and time-dependent manner. Subcellular distribution pattern of both proteins was reversed after irradiation. After irradiation, APE1 that initially showed nuclear localization was gradually increased in the cytoplasm, whereas Nm23-H1 that mainly showed cytoplasmic localization was gradually increased in the nuclei of A549 cells. Nm23-H1 and APE1 interaction was demonstrated by His-pull-down and co-immunoprecipitation assays. The presence of Nm23-H1/APE1 complex in X-ray-irradiated A549 cells was also detected by DNA affinity precipitation analysis of a DNA fragment containing an AP site. Although the AP endonuclease activity of Nm23-H1 was too weak to be detected, the AP endonuclease activity of APE1 was increased with the enhanced Nm23-H1 expression. In conclusion, our data point to a mechanism by which Nm23-H1 protects cells against oxidative stress through the engagement of DNA BER enzyme APE1.

Proteomic analysis of the molecular response of Raji cells to maslinic acid treatment

Maslinic acid, a natural pentacyclic triterpene has been shown to inhibit growth and induce apoptosis in some tumour cell lines. We studied the molecular response of Raji cells towards maslinic acid treatment. A proteomics approach was employed to identify the target proteins. Seventeen differentially expressed proteins including those involved in DNA replication, microtubule filament assembly, nucleo-cytoplasmic trafficking, cell signaling, energy metabolism and cytoskeletal organization were identified by MALDI TOF-TOF MS. The down-regulation of stathmin, Ran GTPase activating protein-1 (RanBP1), and microtubule associated protein RP/EB family member 1 (EB1) were confirmed by Western blotting. The study of the effect of maslinic acid on Raji cell cycle regulation showed that it induced a G1 cell cycle arrest. The differential proteomic changes in maslinic acid-treated Raji cells demonstrated that it also inhibited expression of dUTPase and stathmin which are known to induce early S and G2 cell cycle arrests. The mechanism of maslinic acid-induced cell cycle arrest may be mediated by inhibiting cyclin D1 expression and enhancing the levels of cell cycle-dependent kinase (CDK) inhibitor p21 protein. Maslinic acid suppressed nuclear factor-kappa B (NF-κB) activity which is known to stimulate expression of anti-apoptotic and cell cycle regulatory gene products. These results suggest that maslinic acid affects multiple signaling molecules and inhibits fundamental pathways regulating cell growth and survival in Raji cells.

Sodium valproate inhibits MDA-MB-231 breast cancer cell migration by upregulating NM23H1 expression

Breast cancer is a common cancer in women, with a highly variable course, from inoffensive to lethal. To find a more effective strategy for its treatment, sodium valproate has been tested as an anti-cancer drug; it is the only clinically available histone deacetylase inhibitor. However, data about the effects of sodium valproate on breast cancer are insufficient in both animals and humans; studies have yielded conflicting conclusions. In particular, little is known about the association between expression of the metastasis suppressor Nm23H1 gene and breast cancer. We hypothesized that sodium valproate regulates NM23H1 expression, and affects migration and/or invasion. We found that sodium valproate at concentrations of 0.8-3.2 mM inhibits migration and modulates Nm23H1 gene expression in a concentration-dependent manner. Confluent MDA-MB-231 cells were scratched by a micropipette tip after VPA treatment for 24 h; 24 h later, the scratch was almostly closed in the 0 mM VPA-treated cells, while the 3.2 mM VPA-treated cells migrated the slowest. The cell migration ratio exposed to 0.8, 1.6 and 3.2 mM VPA was about 66.67, 30.67 and 26.67% (P < 0.05). We also found evidence that sodium valproate upregulates NM23H1 expression, which is a clue to its anti-cancer mode of action. The NM23H1 gene expression was relative fold increased determined by Western blotting at 3.2 mM VPA. Collectively, these observations indicate that sodium valproate has potential for use in breast cancer treatment.

The anti-metastatic nm23-1 gene is needed for the final step of mammary duct maturation of the mouse nipple

Nm23/NDP kinases are multifunctional enzymes involved in the general homeostasis of triphosphate nucleosides. Numerous studies have shown that NDPKs also serve as regulatory factors of various cell activities, not always connected to nucleotide phosphorylation. In particular, the nme-1 gene, encoding the NM23-1/NDPKA protein, has been reported as a metastasis suppressor gene. This activity was validated in hepatocellular tumors induced in nm23-1 deficient mice. Yet, data describing the primary physiological functions of nm23-1/NDPKA is still scarce. We have characterized in depth the phenotype of nm23-1 deletion in the mammary gland in mice carrying whole body nm23-M1 invalidation. We also asked why the nm23-M1^−/− mutant females displayed severe nursing disability. We found that the growth retardation of mutant virgin glands was due to reduced proliferation and apoptosis of the epithelial cells within the terminal end buds. The balance of pro/anti-apoptotic factors was impaired in comparison with wild type glands. In the lactating glands, the reduced proliferation rate persisted, but the apoptotic factors were unchanged. However, those defects did not seem to affect the gland maturation since the glands lacking nm23-1/NDPKA appeared morphologically normal. Thorough examination of all the functional aspects of the mammary glands revealed that lack of nm23-1/NDPKA does not impact the production or the ejection of milk in the lumen of lobuloalveolae. Interestingly, an epithelial plug was found to obstruct the extremity of the unique lactiferous duct delivering the milk out of the nipple. These cells, normally disappearing after lactation takes place, persisted in the mutant nipples. This work provides a rare instance of nm23-1/NDPKA physiological functions in the mammary glands and reveals its implication as a modulator factor of proliferation and apoptosis in this tissue.

Mammalian diseases of phosphatidylinositol transfer proteins and their homologs

Inositol and phosphoinositide signaling pathways represent major regulatory systems in eukaryotes. The physiological importance of these pathways is amply demonstrated by the variety of diseases that involve derangements in individual steps in inositide and phosphoinositide production and degradation. These diseases include numerous cancers, lipodystrophies and neurological syndromes. Phosphatidylinositol transfer proteins (PITPs) are emerging as fascinating regulators of phosphoinositide metabolism. Recent advances identify PITPs (and PITP-like proteins) to be coincidence detectors, which spatially and temporally coordinate the activities of diverse aspects of the cellular lipid metabolome with phosphoinositide signaling. These insights are providing new ideas regarding mechanisms of inherited mammalian diseases associated with derangements in the activities of PITPs and PITP-like proteins.

Prognostic significance of co-expression of nm23 and p57 protein in hepatocellular carcinoma

AIM

  To investigate the unbalance of proliferation and apoptosis and the functions of cell-cycle proteins and apoptotic factor in metastasis of hepatocellular carcinoma (HCC) and their effect in prognosis.

METHODS

  Proliferation index and apoptosis index, as well as seven relatively molecular markers, namely p15, p34, p53, p57, p73, survivin and nm23, were evaluated by immunohistochemistry and TUNEL in HCC tissues and compared to adjacent non-cancerous tissues and normal liver tissues. Furthermore, the prognostic significance by follow-up and mutual relationships for each clinicopathologic factor and molecular marker were analysed.

RESULTS

  The dysregulation between proliferation and apoptosis and the abnormal expression of seven molecular markers were observed in HCC tissues. The unbalance of proliferation and apoptosis and abnormal expressions of p15, p34, p57 and nm23 were correlated with TNM stage and extrahepatic metastasis. In particular, the abnormal co-expression of nm23/p57 correlated with advanced TNM stage and bigger tumor size and was an independent prognostic factor of HCC.

CONCLUSION

  The unbalance of proliferation and apoptosis and abnormal expression of cell-cycle proteins promote metastasis of HCC. Moreover, the abnormal co-expression of nm23/p57 may be a useful molecular marker for metastasis and unfavourable prognosis for HCC.

Significance of DR-nm23 protein expression in colorectal carcinoma

AIM: To investigate the relationship between the expression of DR-nm23 protein and the carcinogenesis, progression and metastasis of colorectal carcinoma.

METHODS: Ninety-eight colorectal carcinoma specimens, 57 adenoma specimens and 42 normal colorectal tissue specimens were examined by immunohistochemistry using the streptavidin-peroxidase method. The correlation of DR-nm23 protein expression with the carcinogenesis, progression, lymph node metastasis, histological type and differentiation grade of colorectal carcinoma was then analyzed.

RESULTS: The positive rate of DR-nm23 protein expression was significantly higher in normal colorectal tissue than in adenoma and colorectal carcinoma (71.4% vs 38.6% and 35.7%, respectively; both P < 0.01). The positive rate of DR-nm23 protein expression was significantly lower in high-grade intraepithelial tumors than in low-grade intraepithelial tumors in the adenoma group (25.7% vs 59.1%, P < 0.05), and in metastatic colorectal carcinoma than in non-metastatic colorectal carcinoma (23.1% vs 44.1%, P < 0.05). The expression of DR-nm23 is negatively related to lymph node metastasis (P < 0.05). DR-nm23 expression is also closely related to histological type (χ² = 13.731, P < 0.01) and differentiation grade (χ² = 12.198, P < 0.01). The positive rate of DR-nm23 protein was higher in secondary tumors than in primary tumors in the metastatic colorectal carcinoma group though no significant difference was noted between them (P > 0.05).

CONCLUSION: Decreased DR-nm23 protein expression is closely related to tumor differentiation, carcinogenesis, progression and metastasis in colorectal carcinoma. DR-nm23 is an important parameter for evaluation of the biological behavior and prognosis of colorectal carcinoma.

A Cys/Ser mutation of NDPK-A stabilizes its oligomerization state and enhances its activity

Nucleoside diphosphate phosphate transferase A (NDPK-A) has been shown to play critical roles in the regulation of proliferation, differentiation, growth and apoptosis of cells. Our previous study suggested that the disulphide cross-linkage between cysteine 4 (C4) and cysteine 145 (C145) of NDPK-A might be a possible regulator of its activity. To confirm this hypothesis, the C145 residue of NDPK-A was mutated to serine, and the isomerization and biological activities of the mutant were investigated and compared with those of its wild-type counterpart. It was found the C145S mutation eliminated the intramolecular disulphide bond (DB) and prevented the formation of intermolecular DB, which was known to dissociate the hexameric NDPK-A into dimeric one. We also demonstrated that the C145S mutation didn't affect the autologous hexamerization of this protein, and the mutant had increased bioactivities including phosphate transferase and DNase. These findings support the hypothesis that the formation of DBs in NDPK-A is involved in the regulation of the oligomerization and bioactivity of this multiple function protein, and that C145 is a key residue in the regulation of NDPK-A. In addition, the C145S mutant that we have constructed might be an attractive candidate for use in applications that require NDPK-A.

Plakoglobin interacts with and increases the protein levels of metastasis suppressor Nm23-H2 and regulates the expression of Nm23-H1

Plakoglobin (gamma-catenin) is a homolog of beta-catenin with similar dual adhesive and signaling functions. The adhesive function of these proteins is mediated by their interactions with cadherins, whereas their signaling activity is regulated by association with various intracellular partners. In this respect, beta-catenin has a well-defined oncogenic activity through its role in the Wnt signaling pathway, whereas plakoglobin acts as a tumor/metastasis suppressor through mechanisms that remain unclear. We previously expressed plakoglobin in SCC9 squamous carcinoma cells (SCC9-P) and observed a mesenchymal-to-epidermoid transition. Comparison of the protein and RNA profiles of parental SCC9 cells and SCC9-P transfectants identified various differentially expressed proteins and transcripts, including the nonmetastatic protein 23 (Nm23). In this study, we show that Nm23-H1 mRNA and Nm23-H2 protein are increased after plakoglobin expression. Coimmunoprecipitation and confocal microscopy studies using SCC9-P and various epithelial cell lines with endogenous plakoglobin expression revealed that Nm23 interacts with plakoglobin, cadherins and alpha-catenin. Furthermore, Nm23-H2 is the primary isoform involved in these interactions, which occur prominently in the cytoskeleton-associated pool of cellular proteins. In addition, we show that plakoglobin-Nm23 interaction requires the N-terminal (alpha-catenin interacting) domain of plakoglobin. Our data suggest that by increasing the expression and stability of Nm23, plakoglobin has a role in regulating the metastasis suppressor activity of Nm23, which may further provide a potential mechanism for the tumor/metastasis suppressor function of plakoglobin itself.