NM23-H1 tumor suppressor physically interacts with serine-threonine kinase receptor-associated protein, a transforming growth factor-beta (TGF-beta) receptor-interacting protein, and negatively regulates TGF-beta signaling

PRUNE1 and NME/NDPK family proteins influence energy metabolism and signaling in cancer metastases

We describe here the molecular basis of the complex formation of PRUNE1 with the tumor metastasis suppressors NME1 and NME2, two isoforms appertaining to the nucleoside diphosphate kinase (NDPK) enzyme family, and how this complex regulates signaling the immune system and energy metabolism, thereby shaping the tumor microenvironment (TME). Disrupting the interaction between NME1/2 and PRUNE1, as suggested, holds the potential to be an excellent therapeutic target for the treatment of cancer and the inhibition of metastasis dissemination. Furthermore, we postulate an interaction and regulation of the other Class I NME proteins, NME3 and NME4 proteins, with PRUNE1 and discuss potential functions. Class I NME1-4 proteins are NTP/NDP transphosphorylases required for balancing the intracellular pools of nucleotide diphosphates and triphosphates. They regulate different cellular functions by interacting with a large variety of other proteins, and in cancer and metastasis processes, they can exert pro- and anti-oncogenic properties depending on the cellular context. In this review, we therefore additionally discuss general aspects of class1 NME and PRUNE1 molecular structures as well as their posttranslational modifications and subcellular localization. The current knowledge on the contributions of PRUNE1 as well as NME proteins to signaling cascades is summarized with a special regard to cancer and metastasis.

Integrin beta-like 1 mediates fibroblast-cardiomyocyte crosstalk to promote cardiac fibrosis and hypertrophy

AIMS

Crosstalk between fibroblasts and cardiomyocytes (CMs) plays a critical role in cardiac remodelling during heart failure (HF); however, the underlying molecular mechanisms remain obscure. Recently, a secretory protein, Integrin beta-like 1 (ITGBL1) was revealed to have detrimental effects on several diseases, such as tumours, pulmonary fibrosis, and hepatic fibrosis; whereas the effect of ITGBL1 on HF is unclear. The purpose of this study was to evaluate its contribution to volume overload-induced remodelling.

METHODS AND RESULTS

In this study, we identified ITGBL1 was highly expressed in varied heart diseases and validated in our TAC mice model, especially in fibroblasts. To investigate the role of ITGBL1 in in vitro cell experiments, neonatal rat fibroblasts (NRCFs) and cardiomyocytes (NRCMs) were performed for further study. We found that in comparison to NRCMs, NRCFs expressed high levels of ITGBL1. Meanwhile, ITGBL1 was upregulated in NRCFs, but not in NRCMs following angiotensin-II (AngII) or phenylephrine stimulation. Furthermore, ITGBL1 overexpression promoted NRCFs activation, whereas knockdown of ITGBL1 alleviated NRCFs activation under AngII treatment. Moreover, NRCFs-secreted ITGBL1 could induce NRCMs hypertrophy. Mechanically, ITGBL1-NME/NM23 nucleoside diphosphate kinase 1 (NME1)-TGF-β-Smad2/3 and Wnt signalling pathways were identified to mediate NRCFs activation and NRCMs hypertrophy, respectively. Finally, the knockdown of ITGBL1 in mice subjected to transverse aortic constriction (TAC) surgery recapitulated the in vitro findings, demonstrating blunted cardiac fibrosis, hypertrophy, and improved cardiac function.

CONCLUSIONS

ITGBL1 is an important functional mediator between fibroblast-cardiomyocyte crosstalk and could be an effective target for cardiac remodelling in HF patients.

Heterochiral dipeptide d-phenylalanyl- l-phenylalanine (H-D Phe-L Phe-OH) as a potential inducer of metastatic suppressor NM23H1 in p53 wild-type and mutant cells

In recent years, significant progress has been made to the use-case of small peptides because of their diversified edifice and hence their versatile application scope in cancer therapy. Here we identify the heterochiral dipeptide H-^D Phe-^L Phe-OH (F1) as a potent inducer of the metastatic suppressor NM23H1. We divulge the effect of F1 on the major EMT/metastasis-associated genes and the implications on the invasion and migration ability of cancer cells. The anti-invasive potential of F1 was directly correlated with NM23H1 expression. Mechanistically, F1 treatment elevated p53 levels as validated by localization and transcriptional studies. In the NM23H1 knockdown condition, F1 failed to induce any p53 expression/nuclear localization, indicating that the upregulation in p53 expression by F1 is NM23H1 dependent. We also demonstrate how the antimetastatic potential of F1 is primarily mediated through NM23H1 irrespective of the p53 status of the cell. However, both NM23H1 and a functional p53 protein in conjunction govern the apoptotic and cytostatic potential of F1. Coimmunoprecipitation studies unraveled the augmentation of the p53 and NM23H1 interaction in p53 wild-type cells. However, in p53 mutated cells, no such enrichment was evidenced. We employed mouse isogenic cell lines (4T-1 and 4T-1 p53) to determine the in vivo efficacy of F1 (spontaneous and experimental models). Decreased tumor volume in the cohort injected with 4T-1 p53 cells demonstrated that while the antimetastatic potential of F1 was reliant on NM23H1, p53 activation was required for ablation of primary tumor burden. Our findings unravel that F1 treatment induces significant abrogation of the migration, invasion and metastatic potential of both p53 wild-type and p53 deficient cancers mediated through NM23H1.

NM23 Is a CP-Binding Protein Involved in Infectious Hypodermal and Hematopoietic Necrosis Virus Infection in Shrimp

Simple Summary

In this study, we aimed to identify the putative host cell receptor for Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) CP(Capsid Protein) in the gill membrane of LitoPenaeus vannamei. We established that NM23 is a host cell binding partner for IHHNV CP. Our study is probably the first to address the host cell IHHNV receptor and could provide novel insights into the pathogenesis of IHHNV. We feel that this paper is of interest to the readers of Animals.

Abstract

The aim of this study was to identify the putative host cell receptor for Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) CP in the gill membrane of L. vannamei. Putative CP binding partners were screened first using a 2-dimensional Virus Overlay Protein Blot Assay (VOPBA) to probe isolated gill membrane proteins using recombinant CP. Putative binding partners were identified using mass spectrometry. A Phage Display Random Dodecapeptide Library was used to screen for dodecapeptides and motifs that bound to CP. Finally, putative binding pairs were confirmed using GST(glutathione-S-transferase) pulldown assays. 2-Dimensional VOPBA identified NM23 as a putative binding partner for IHHNV CP. GST pulldown experiments confirmed the direct interaction of NM23 and IHHNV CP. The phage display library was used to identify six groups of dodecapeptides that bound to CP. From these peptides, three characteristic binding motifs were identified, SW*Y, SKWV, and PQR. Interestingly, the SW*Y motif was also found in NM23. We are the first to implicate NM23 in IHHNV infection and postulate that it may bind to the CP using the SW*Y motif, although this remains to be confirmed.

First Attempt to Couple Proteomics with the AhR Reporter Gene Bioassay in Soil Pollution Monitoring and Assessment

A topsoil sample obtained from a highly industrialized area (Taranto, Italy) was tested on the DR-CALUX^® cell line and the exposed cells processed with proteomic and bioinformatics analyses. The presence of polyhalogenated compounds in the topsoil extracts was confirmed by GC-MS/MS analysis. Proteomic analysis of the cells exposed to the topsoil extracts identified 43 differential proteins. Enrichment analysis highlighted biological processes, such as the cellular response to a chemical stimulus, stress, and inorganic substances; regulation of translation; regulation of apoptotic process; and the response to organonitrogen compounds in light of particular drugs and compounds, extrapolated by bioinformatics all linked to the identified protein modifications. Our results confirm and reflect the complex epidemiological situation occurring among Taranto inhabitants and underline the need to further investigate the presence and sources of inferred chemicals in soils. The combination of bioassays and proteomics reveals a more complex scenario of chemicals able to affect cellular pathways and leading to toxicities rather than those identified by only bioassays and related chemical analysis. This combined approach turns out to be a promising tool for soil risk assessment and deserves further investigation and developments for soil monitoring and risk assessment.

Clinicopathological and prognostic significance of NM23 expression in patients with non-small cell lung cancer: A systematic review and meta-analysis

BACKGROUND

There is a heated debate on the clinicopathological features and prognostic significance with non-metastasis 23 (NM23) expression in patients with non-small cell lung cancer (NSCLC). Thus, we conducted this meta-analysis to evaluate the clinicopathological features and prognostic significance of NM23 for NSCLC patients.

METHODS

Pubmed, Embase, and Web of Science were exhaustively searched to identify relevant studies published prior to March, 2020. Odds radios (ORs) and hazard radios with 95% confidence intervals (CIs) were calculated to summarize the statistics of clinicopathological and prognostic assessments. Q-test and I2-statistic were utilized to assess heterogeneity across the included studies. We also performed subgroup analyses and meta-regression analyses to identify the source of heterogeneity. Publication bias was detected by Begg and Egger tests. Sensitivity analysis was used to value the stability of our results. All the data were analyzed using statistical packages implemented in R version 4.0.5.

RESULTS

Data from a total of 3170 patients from 36 studies were extracted. The meta-analysis revealed that low expression of NM23 was correlated with higher risk of NSCLC (OR = 4.35; 95% CI: 2.76-6.85; P < .01), poorer tumor node metastasis (TNM) staging (OR = 1.39; 95% CI: 1.01-1.90; P = .04), poorer differentiation degree (OR = 1.37; 95% CI: 1.01-1.86; P = .04), positive lymph node metastasis (OR = 1.83; 95% CI: 1.22-2.74; P < .01), lung adenocarcinoma (OR = 1.45; 95% CI: 1.20-1.75; P < .01), and poorer 5-year overall survival (OS) rate (hazard radio = 2.33; 95%CI: 1.32-4.11; P < .01). The subgroup analyses and meta-regression analyses suggested that the "Publication year", "Country", "Sample size", and "Cutoff value" might be the source of heterogeneity in TNM staging, differentiation degree, and lymph node metastasis. Both Begg test and Egger test verified that there were publication bias in 5-year OS rate. Sensitivity analysis supported the credibility of the results.

CONCLUSION

The reduced NM23 expression is strongly associated with higher risk of NSCLC, higher TNM staging, poorer differentiation degree, positive lymph node metastasis, lung adenocarcinoma, and poorer 5-year OS rate in NSCLC patients, which indicated that NM23 could serve as a biomarker predicating the clinicopathological and prognostic significance of NSCLC.

STRAP and NME1 Mediate the Neurite Growth-Promoting Effects of the Neurotrophic Factor GDF5

Loss of midbrain dopaminergic (mDA) neurons and their axons is central to Parkinson's disease (PD). Growth differentiation factor (GDF)5 is a potential neurotrophic factor for PD therapy. However, the molecular mediators of its neurotrophic action are unknown. Our proteomics analysis shows that GDF5 increases the expression of serine threonine receptor-associated protein kinase (STRAP) and nucleoside diphosphate kinase (NME)1 in the SH-SY5Y neuronal cell line. GDF5 overexpression increased NME1 expression in adult rat brain in vivo. NME and STRAP mRNAs are expressed in developing and adult rodent midbrain. Expression of both STRAP and NME1 is necessary and sufficient for the promotion of neurite growth in SH-SY5Y cells by GDF5. NME1 treatment increased neurite growth in both SH-SY5Y cells and cultured mDA neurons. Expression patterns of NME and STRAP are altered in PD midbrain. NME1 and STRAP are thus key mediators of GDF5's neurotrophic effects, rationalizing their future study as therapeutic targets for PD.

Histidine kinase NME1 and NME2 are involved in TGF-β1-induced HSC activation and CCl4-induced liver fibrosis

Histidine phosphorylation (pHis) was first reported in 1962. There are few studies on pHis because of the thermal and acidic instability of pHis and the lack of specific methods to detect it. pHis has two isomers of 1-phosphate histidine (1-pHis) and 3-phosphate histidine (3-pHis). pHis antibodies have been developed recently and have promoted research in this field. In this study, we established a CCl₄-induced liver fibrosis model in C57 mice and a TGF-β1-induced HSC activation model in LX-2 cells, to study the role of histidine phosphorylation. The expression of histidine kinases NME1 and NME2 was increased, histidine phosphatase PGAM5 and PHPT1 was unchanged, and 1-pHis and 3-pHis were increased in the in vivo and in vitro models. The expression of LHPP was decreased in the in vivo model but not in the in vitro model. To further study the role of NME1, NME2, and histidine phosphorylation in HSC activation, we silenced NME1 or NME2 and administered TGF-β1 in LX-2 cells. The results showed silencing NME1 or NME2 decreased TGF-β1-induced pHis levels and the expression of α-SMA and COL1A1, indicating the activation of HSC was suppressed. Then, we found the inhibitory effect on HSC activation is due to reduced phosphorylation of Smad2 and Smad3. In summary, our studies indicate that NME1 and NME2 are involved in TGF-β1-induced HSC activation and CCl₄-induced liver fibrosis, which may be mediated by histidine phosphorylation.

Par-4 mediated Smad4 induction in PDAC cells restores canonical TGF-β/ Smad4 axis driving the cells towards lethal EMT

Deregulation of TGF-β signaling is intricately engrossed in the pathophysiology of pancreatic adenocarcinomas (PDACs). The role of TGF-β all through pancreatic cancer initiation and progression is multifarious and somewhat paradoxical. TGF-β plays a tumor suppressive role in early-stage pancreatic cancer by promoting apoptosis and inhibiting epithelial cell cycle progression, but incites tumor promotion in late-stage by modulating genomic instability, neo-angiogenesis, immune evasion, cell motility, and metastasis. Here, we provide evidences that Par-4 acts as one of the vital mediators to regulate TGF-β/Smad4 pathway, wherein, Par-4 induction/over-expression induced EMT which was later culminated in to apoptosis in presence of TGF-β via positive regulation of Smad4. Intriguingly, Par-4^-/- cells were devoid of significant Smad4 induction compared to Par-4^+/+ cells in presence of TGF-β and ectopic Par-4 steadily augmented Smad4 expression by restoring TGF-β/Smad4 axis in Panc-1 cells. Further, our FACS and western blotting results unveiled that Par-4 dragged the PDAC cells to G₁ arrest in presence of TGF-β byelevating p21 and p27 levels while attenuating Cyclin E and A levels and augmenting caspase 3 cleavage triggering lethal EMT. Through restoration of Smad4, we further establish that in BxPC3 cell line (Smad4^-/-), Smad4 is essential for Par-4 to indulge TGF-β dependent lethal EMT program. The mechanistic relevance of Par-4 mediated Smad4 activation was additionally validated by co-immunoprecipitation wherein disruption of NM23H1-STRAP interaction by Par-4 rescues TGF-β/Smad4 pathway in PDAC and mediates the tumor suppressive role of TGF-β, therefore serving as a vital cog to restore the apoptotic functions of TGF-β pathway.

Opposite functions of GSN and OAS2 on colorectal cancer metastasis, mediating perineural and lymphovascular invasion, respectively

The present study aimed to identify molecules associated with lymphovascular invasion (LVI) and perineural invasion (PNI) and to examine their biological behavior in colorectal cancer (CRC). LVI- and PNI-associated molecules were identified and verified using sequential processes including (1) identification of 117 recurrence-associated genes differentially expressed on RNA-seq analysis using primary cancer tissues from 130 CRC patients with and without systemic recurrence; (2) analysis of molecules associated with LVI and PNI; (3) assessment of biological properties by measuring proliferation, anoikis, invasion/migration, epithelial-mesenchymal transition and autophagy flux; and (4) verification of disease-free survival using public datasets. Gelsolin (GSN) and 2'-5'-oligoadenylate synthetase 2 (OAS2) were associated with PNI and LVI, respectively. Invasion potential was >2-fold greater in GSN-overexpressing LoVo cells than in control cells (p<0.001–0.005), whereas OAS2-overexpressing RKO cells showed reduced invasion (p<0.001–0.005). GSN downregulated E-cadherin, β-catenin, claudin-1 and snail, and upregulated N-cadherin and ZEB1, whereas OAS2 overexpression had the opposite effects. Several autophagy-related proteins including ATG5-12, ATG6/BECN1, ATG7 and ATG101 were downregulated in GSN-overexpressing LoVo cells, whereas the opposite pattern was observed in OAS2-overexpressing RKO cells. Patients with low GSN expression had significantly higher 5-year recurrence-free survival (RFS) rates than those with GSN overexpression (73.6% vs. 64.7%, p = 0.038), whereas RFS was longer in patients with OAS2 overexpression than in those with underexpression (73.4% vs. 63.7%, p = 0.01). In conclusion, GSN and OAS2 were positively and negatively associated with recurrence, respectively, suggesting their potential value as predictors of recurrence or therapeutic targets in CRC patients.

Dual Roles of Serine-Threonine Kinase Receptor-Associated Protein (STRAP) in Redox-Sensitive Signaling Pathways Related to Cancer Development

Serine-threonine kinase receptor-associated protein (STRAP) is a transforming growth factor β (TGF-β) receptor-interacting protein that has been implicated in both cell proliferation and cell death in response to various stresses. However, the precise roles of STRAP in these cellular processes are still unclear. The mechanisms by which STRAP controls both cell proliferation and cell death are now beginning to be unraveled. In addition to its biological roles, this review also focuses on the dual functions of STRAP in cancers displaying redox dysregulation, where it can behave as a tumor suppressor or an oncogene (i.e., it can either inhibit or promote tumor formation), depending on the cellular context. Further studies are needed to define the functions of STRAP and the redox-sensitive intracellular signaling pathways that enhance either cell proliferation or cell death in human cancer tissues, which may help in the development of effective treatments for cancer.

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.

NM23/NDPK proteins in transcription regulatory functions and chromatin modulation: emerging trends

NM23/NDPK proteins have been studied for their metastasis suppressor role but the molecular pathways involved in this process are not very vivid. Nucleotide binding and kinase activities of NM23 proteins implicated in anti-metastatic effects have been widely studied. In addition to these, transcriptional regulation adds another arm to the versatility of NM23 proteins that together with the other functions may contribute to better understanding of underlying mechanisms. In this review we discuss emerging reports describing the role of NM23 proteins in gene regulation and chromatin modulation in association with other factors or on their own.

Correlation between NM23 protein overexpression and prognostic value and clinicopathologic features of ovarian cancer: a meta-analysis

OBJECTIVE

The prognostic value and clinicopathological features of NM23 (non-metastasis 23) have previously been assessed, but the results are controversial. Here, we attempted to clarify the correlation between NM23 expression and its prognostic value and the clinicopathological features in ovarian cancer (OC).

METHODS

The relevant studies were identified using PubMed, Embase, and Web of Science. We calculated the pooled odds ratio (OR) with 95% confidence intervals (CIs) for overall survival (OS), progression-free survival (PFS), and clinicopathological features. We used OS to evaluate the prognostic value of NM23 expression in patients with OC. Subgroup analyses were used to explore the source of heterogeneity.

RESULTS

We included 10 studies involving 894 patients in our assessment of the association between NM23 expression and OS for OC. Our data indicated that NM23 expression was not associated with improved OS (OR 0.83, 95% CI 0.41-1.68, P = 0.61) or PFS (OR 0.7, 95% CI 0.39-1.24, P = 0.22). Elevated NM23 expression was associated with differentiation grade (OR 0.35, 95% CI 0.2-0.6, P = 0.0002) and N status (OR 0.33, 95% CI 0.14-0.78, P = 0.01), whereas there was no significant difference between NM23 expression and tumor stage (OR 1.1, 95% CI 0.45-2.66, P = 0.84). Subgroup analysis did not reveal any potential source of heterogeneity. No obvious publication bias was found.

CONCLUSIONS

In OC, there is poor statistical significance between NM23 expression and OS and PFS, but NM23 expression is related to differentiation grade and N status. This meta-analysis reveals that NM23 expression is a potential factor of poor prognosis in OC. The prognostic role of NM23 in different OC stages in combination with the clinical characteristics suggests a novel approach for developing future therapeutic targets.

Novel role of STRAP in progression and metastasis of colorectal cancer through Wnt/β-catenin signaling

Serine-Threonine Kinase Receptor-Associated Protein (STRAP) interacts with a variety of proteins and influences a wide range of cellular processes. Aberrant activation of Wnt/β-catenin signaling has been implicated in the development of colorectal cancer (CRC). Here, we show the molecular mechanism by which STRAP induces CRC metastasis by promoting β-catenin signaling through its stabilization. We have genetically engineered a series of murine and human CRC and lung cancer cell lines to investigate the effects of STRAP on cell migration and invasion in vitro, and on tumorigenicity and metastasis in vivo. Downregulation of STRAP inhibits invasion, tumorigenicity, and metastasis of CRC cells. Mechanistically, STRAP binds with GSK-3β and reduces the phosphorylation, ubiquitylation, and degradation of β-catenin through preventing its binding to the destruction complex. This leads to an inhibition of Wnt/β-catenin signaling and reduction in the expression of downstream targets, such as Cyclin D1, matrix metalloproteinases 2 and 9, and ß-TrCP. In human CRC specimens, higher STRAP expression correlates significantly with β-catenin expression with increased nuclear levels (R =0.696, p < .0001, n =128). Together, these results suggest that STRAP increases invasion and metastasis of CRC partly through inhibiting ubiquitin-dependent degradation of β-catenin and promoting Wnt/β-catenin signaling.

Zinc finger protein ZPR9 functions as an activator of AMPK-related serine/threonine kinase MPK38/MELK involved in ASK1/TGF-β/p53 signaling pathways

Murine protein serine-threonine kinase 38 (MPK38), an AMP-activated protein kinase (AMPK)-related kinase, has been implicated in the induction of apoptosis signal-regulating kinase 1 (ASK1)-, transforming growth factor-β (TGF-β)-, and p53-mediated activity involved in metabolic homeostasis. Here, zinc finger protein ZPR9 was found to be an activator of MPK38. The association of MPK38 and ZPR9 was mediated by cysteine residues present in each of these two proteins, Cys²⁶⁹ and Cys²⁸⁶ of MPK38 and Cys³⁰⁵ and Cys³⁰⁸ of ZPR9. MPK38 phosphorylated ZPR9 at Thr²⁵². Wild-type ZPR9, but not the ZPR9 mutant T252A, enhanced ASK1, TGF-β, and p53 function by stabilizing MPK38. The requirement of ZPR9 Thr²⁵² phosphorylation was validated using CRISPR/Cas9-mediated ZPR9 (T252A) knockin cell lines. The knockdown of endogenous ZPR9 showed an opposite trend, resulting in the inhibition of MPK38-dependent ASK1, TGF-β, and p53 function. This effect was also demonstrated in mouse embryonic fibroblast (MEF) cells that were haploinsufficient (+/-) for ZPR9, NIH 3T3 cells with inducible knockdown of ZPR9, and CRISPR/Cas9-mediated ZPR9 knockout cells. Furthermore, high-fat diet (HFD)-fed mice displayed reduced MPK38 kinase activity and ZPR9 expression compared to that in mice on control chow, suggesting that ZPR9 acts as a physiological activator of MPK38 that may participate in obesity.

Signaling Receptors for TGF-β Family Members

Transforming growth factor β (TGF-β) family members signal via heterotetrameric complexes of type I and type II dual specificity kinase receptors. The activation and stability of the receptors are controlled by posttranslational modifications, such as phosphorylation, ubiquitylation, sumoylation, and neddylation, as well as by interaction with other proteins at the cell surface and in the cytoplasm. Activation of TGF-β receptors induces signaling via formation of Smad complexes that are translocated to the nucleus where they act as transcription factors, as well as via non-Smad pathways, including the Erk1/2, JNK and p38 MAP kinase pathways, and the Src tyrosine kinase, phosphatidylinositol 3'-kinase, and Rho GTPases.

Characterization of Functional Domains in NME1L Regulation of NF-κB Signaling

NME1 is a well-known metastasis suppressor which has been reported to be downregulated in some highly aggressive cancer cells. Although most studies have focused on NME1, the NME1 gene also encodes the protein (NME1L) containing N-terminal 25 extra amino acids by alternative splicing. According to previous studies, NME1L has potent anti-metastatic activity, in comparison with NME1, by interacting with IKKβ and regulating its activity. In the present study, we tried to define the role of the N-terminal 25 amino acids of NME1L in NF-κB activation signaling. Unfortunately, the sequence itself did not interact with IKKβ, suggesting that it may be not enough to constitute the functional structure. Further construction of NME1L fragments and biochemical analysis revealed that N-terminal 84 residues constitute minimal structure for homodimerization, IKKβ interaction and regulation of NF-κB signaling. The inhibitory effect of the fragment on cancer cell migration and NF-κB-stimulated gene expression was equivalent to that of whole NME1L. The data suggest that the N-terminal 84 residues may be a core region for the anti-metastatic activity of NME1L. Based on this result, further structural analysis of the binding between NME1L and IKKβ may help in understanding the anti-metastatic activity of NME1L and provide direction to NME1L and IKKβ-related anti-cancer drug design.

Reduced NM23 Protein Level Correlates With Worse Clinicopathologic Features in Colorectal Cancers: A Meta-Analysis of Pooled Data

The clinical value of a prominent metastasis suppressor, nonmetastatic protein 23 (NM23), remains controversial. In this study, we examined the correlation between NM23 protein levels and the clinicopathologic features of colorectal cancers (CRC), and assessed the overall prognostic value of NM23 for CRC. Embase, PubMed, Web of Science, and other scientific literature databases were exhaustively searched to identify relevant studies published prior to June 31, 2015. The methodological qualities of selected studies were scored based on the critical appraisal skills program (CASP) criteria, as independently assessed by 2 reviewers. NM23 protein levels in tumor tissues of CRC patients were examined in relation to Dukes stage, differentiation grade, T-stage, lymph node metastasis status, and overall survival (OS). STATA software version 12.0 (Stata Corp, College Station, TX) was used for statistical analysis of data pooled from selected studies. Nineteen cohort studies met the inclusion criteria for present study and contained a combined total of 2148 study subjects. Pooled odd ratios (ORs) for NM23 expression revealed that reduced NM23 protein levels in CRC tumor tissues correlated with Dukes stage C and D (OR = 1.89, 95% CI: 1.06-3.39, P = 0.032), poor differentiation grades (OR = 1.41, 95% CI: 1.03-1.94, P = 0.032), and positive lymph node metastasis status (OR = 3.21, 95% CI: 1.95-5.29, P < 0.001). On the other hand, no such correlations were evident with T-stage T3-4 (OR = 1.56, 95% CI: 0.60-4.06, P = 0.367) or OS (OR = 0.79, 95% CI: 0.58-1.08, P = 0.138). Our analysis of pooled data found that NM23 expression is reduced in CRC tissues and low NM23 levels tightly correlate with higher Dukes stages, poorer differentiation grade, and positive lymph node metastases. However, NM23 levels did not influence the OS in CRC patients.

Mice with Hepatic Loss of the Desmosomal Protein γ-Catenin Are Prone to Cholestatic Injury and Chemical Carcinogenesis

γ-Catenin, an important component of desmosomes, may also participate in Wnt signaling. Herein, we dissect the role of γ-catenin in liver by generating conditional γ-catenin knockout (KO) mice and assessing their phenotype after bile duct ligation (BDL) and diethylnitrosamine-induced chemical carcinogenesis. At baseline, KO and wild-type littermates showed comparable serum biochemistry, liver histology, and global gene expression. β-Catenin protein was modestly increased without any change in Wnt signaling. Desmosomes were maintained in KO, and despite no noticeable changes in gene expression, differential detergent fractionation revealed quantitative and qualitative changes in desmosomal cadherins, plaque proteins, and β-catenin. Enhanced association of β-catenin to desmoglein-2 and plakophilin-3 was observed in KO. When subjected to BDL, wild-type littermates showed specific changes in desmosomal protein expression. In KO, BDL deteriorated baseline compensatory changes, which manifested as enhanced injury and fibrosis. KO also showed enhanced tumorigenesis to diethylnitrosamine treatment because of Wnt activation, as also verified in vitro. γ-Catenin overexpression in hepatoma cells increased its binding to T-cell factor 4 at the expense of β-catenin-T-cell factor 4 association, induced unique target genes, affected Wnt targets, and reduced cell proliferation and viability. Thus, γ-catenin loss in liver is basally well tolerated. However, after insults like BDL, these compensations at desmosomes fail, and KO show enhanced injury. Also, γ-catenin negatively regulates tumor growth by affecting Wnt signaling.

A crucial role for the phosphorylation of STRAP at Ser(188) by MPK38 in STRAP-dependent cell death through ASK1, TGF-β, p53, and PI3K/PDK1 signaling pathways

Serine-threonine kinase receptor-associated protein (STRAP) is a TGF-β receptor-interacting protein that participates in the regulation of cell proliferation and cell death in response to various stresses. Here, we demonstrate that STRAP phosphorylation plays an important role in determining the pro- or anti-apoptotic function of STRAP. Murine protein serine/threonine kinase 38 (MPK38) phosphorylates STRAP at Ser(188) via direct interaction. Complex formation between STRAP and MPK38 is mediated by Cys(152) and Cys(270) of STRAP and Cys(339) and Cys(377) of MPK38, suggesting the redox dependency of this interaction. MPK38-mediated STRAP Ser(188) phosphorylation contributes to the pro-apoptotic function of STRAP by modulating key steps in STRAP-dependent ASK1, TGF-β, p53, and PI3K/PDK1 signaling pathways. Moreover, knockdown of endogenous MPK38 using an inducible MPK38 shRNA system and in vivo activation of MPK38 by treatment of HEK293 and STRAP-null MEF cells with 1-chloro-2,4-dinitrobenzene (DNCB), a specific inhibitor of Trx reductase, provide evidence that STRAP Ser(188) phosphorylation plays a key role in STRAP-dependent cell death. Adenoviral delivery of MPK38 in mice also demonstrates that STRAP Ser(188) phosphorylation in the liver is tightly associated with cell death and proliferation through ASK1, TGF-β, p53, and PI3K/PDK1 pathways, resulting in apoptotic cell death.

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 splicing variant of NME1 negatively regulates NF-κB signaling and inhibits cancer metastasis by interacting with IKKβ

IKKβ functions as a principal upstream activator of the canonical NF-κB pathway by phosphorylating IκB, leading to its proteasomal degradation. Because IKKβ is considered a therapeutic target, understanding its regulation may facilitate the design of efficient regulators of this molecule. Here, we report a novel IKKβ-interacting molecule, NME1L, a splicing variant of the NME1 protein. NME1 has attracted attention in cancer research because of its antimetastatic activity and reduced expression in multiple aggressive types of cancer. However, the effect was just moderate but not dramatic in anti-cancer activities. We found that only NME1L interacts with IKKβ. Exogenous expression of NME1L resulted in a potent decrease in TNFα-stimulated NF-κB activation, whereas knockdown of NME1/NME1L with shRNA enhanced activity of NF-κB. NME1L down-regulates IKKβ signaling by blocking IKKβ-mediated IκB degradation. When NME1L was introduced into highly metastatic HT1080 cells, the mobility was efficiently inhibited. Furthermore, in a metastasis assay, NME1L-expressing cells did not colonize the lung. Based on these results, NME1L is a potent antimetastatic protein and may be a useful weapon in the fight against cancers.

Computational identification of potential transcriptional regulators of TGF-ß1 in human atherosclerotic arteries

TGF-ß is protective in atherosclerosis but deleterious in metastatic cancers. Our aim was to determine whether TGF-ß transcriptional regulation is tissue-specific in early atherosclerosis. The computational methods included 5 steps: (i) from microarray data of human atherosclerotic carotid tissue, to identify the 10 best co-expressed genes with TGFB1 (TGFB1 gene cluster), (ii) to choose the 11 proximal promoters, (iii) to predict the TFBS shared by the promoters, (iv) to identify the common TFs co-expressed with the TGFB1 gene cluster, and (v) to compare the common TFs in the early lesions to those identified in advanced atherosclerotic lesions and in various cancers. Our results show that EGR1, SP1 and KLF6 could be responsible for TGFB1 basal expression, KLF6 appearing specific to atherosclerotic lesions. Among the TFs co-expressed with the gene cluster, transcriptional activators (SLC2A4RG, MAZ) and repressors (ZBTB7A, PATZ1, ZNF263) could be involved in the fine-tuning of TGFB1 expression in atherosclerosis.

Erythropoietin increases neuronal NDPKA expression, and NDPKA up-regulation as well as exogenous application protects cortical neurons from in vitro ischemia-related insults

Using proteomics, we identified nucleoside diphosphate kinase A (NDPKA; also known as NME/NM23 nucleoside diphosphate kinase 1: NME1) to be up-regulated in primary cortical neuronal cultures by erythropoietin (EPO) preconditioning. To investigate a neuroprotective role of NDPKA in neurons, we used a RNAi construct to knock-down and an adenoviral vector to overexpress the protein in cortical neuronal cultures prior to exposure to three ischemia-related injury models; excitotoxicity (L-glutamic acid), oxidative stress (hydrogen peroxide), and in vitro ischemia (oxygen-glucose deprivation). NDPKA down-regulation had no effect on neuronal viability following injury. By contrast, NDPKA up-regulation increased neuronal survival in all three-injury models. Similarly, treatment with NDPKA recombinant protein increased neuronal survival, but only against in vitro ischemia and excitotoxicity. These findings indicate that the NDPKA protein may confer a neuroprotective advantage following injury. Furthermore, as exogenous NDPKA protein was neuroprotective, it suggests that a cell surface receptor may be activated by NDPKA leading to a protective cell-signaling response. Taken together both NDPKAs intracellular and extracellular neuroprotective actions suggest that the protein is a legitimate therapeutic target for the design of drugs to limit neuronal death following stroke and other forms of brain injury.

Proteomic analysis of proton beam irradiated human melanoma cells

Proton beam irradiation is a form of advanced radiotherapy providing superior distributions of a low LET radiation dose relative to that of photon therapy for the treatment of cancer. Even though this clinical treatment has been developing for several decades, the proton radiobiology critical to the optimization of proton radiotherapy is far from being understood. Proteomic changes were analyzed in human melanoma cells treated with a sublethal dose (3 Gy) of proton beam irradiation. The results were compared with untreated cells. Two-dimensional electrophoresis was performed with mass spectrometry to identify the proteins. At the dose of 3 Gy a minimal slowdown in proliferation rate was seen, as well as some DNA damage. After allowing time for damage repair, the proteomic analysis was performed. In total 17 protein levels were found to significantly (more than 1.5 times) change: 4 downregulated and 13 upregulated. Functionally, they represent four categories: (i) DNA repair and RNA regulation (VCP, MVP, STRAP, FAB-2, Lamine A/C, GAPDH), (ii) cell survival and stress response (STRAP, MCM7, Annexin 7, MVP, Caprin-1, PDCD6, VCP, HSP70), (iii) cell metabolism (TIM, GAPDH, VCP), and (iv) cytoskeleton and motility (Moesin, Actinin 4, FAB-2, Vimentin, Annexin 7, Lamine A/C, Lamine B). A substantial decrease (2.3 x) was seen in the level of vimentin, a marker of epithelial to mesenchymal transition and the metastatic properties of melanoma.

Thioredoxin inhibits MPK38-induced ASK1, TGF-β, and p53 function in a phosphorylation-dependent manner

Murine protein serine-threonine kinase 38 (MPK38) is a member of the AMP-activated protein kinase-related serine/threonine kinase family. The factors that regulate MPK38 activity and function are not yet elucidated. Here, thioredoxin (Trx) was shown to be a negative regulator of MPK38. The redox-dependent association of MPK38 and Trx was mediated through the C-terminal domain of MPK38. Single and double amino acid substitution mutagenesis of MPK38 (C286S, C339S, C377S, and C339S/C377S) and Trx (C32S, C35S, and C32S/C35S) demonstrated that Cys(339) and Cys(377) of MPK38 and Cys(32) and Cys(35) of Trx are required for MPK38-Trx complex formation. MPK38 directly interacted with and phosphorylated Trx at Thr(76). Expression of wild-type Trx, but not the Trx mutants C32S/C35S and T76A, inhibited MPK38-induced ASK1, TGF-β, and p53 function by destabilizing MPK38. The E3 ubiquitin-protein ligase Mdm2 played a critical role in the regulation of MPK38 stability by Trx. Treatment of cells with 1-chloro-2,4-dinitrobenzene, a specific inhibitor of Trx reductase, decreased MPK38-Trx complex formation and subsequently increased MPK38 stability and activity, indicating that Trx negatively regulates MPK38 activity in vivo. Finally, we used ASK1-, Smad3-, and p53-null mouse embryonic fibroblasts to demonstrate that ASK1, Smad3, and p53 play important roles in the activity and function of MPK38, suggesting a functional link between MPK38 and ASK1, TGF-β, and p53 signaling pathways. These results indicate that Trx functions as a physiological inhibitor of MPK38, which plays an important role in inducing ASK1-, TGF-β-, and p53-mediated activity.

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.

TLR4 ligand/H₂O₂ enhances TGF-β1 signaling to induce metastatic potential of non-invasive breast cancer cells by activating non-Smad pathways

TGF-β1 has the potential to activate multiple signaling pathways required for inducing metastatic potential of tumor cells. However, TGF-β1 was inefficient in inducing metastatic potential of many non-invasive human tumor cells. Here we report that the enhancement of TGF-β1 signaling is required for inducing metastatic potential of non-invasive breast cancer cells. TGF-β1 alone could not efficiently induce the sustained activation of Smad and non-Smad pathways in non-invasive breast cancer cells. TLR4 ligand (LPS) and H₂O₂ cooperated with TGF-β1 to enhance the sustained activation of non-Smad pathways, including p38MAPK, ERK, JNK, PI3K, and NF-κB. The activation of MAPK and PI3K pathways resulted in a positive feed-back effect on TGF-β1 signaling by down-regulating Nm23-H1 expression and up-regulating the expression of TβRI and TβRII, favoring further activation of multiple signaling pathways. Moreover, the enhanced TGF-β1 signaling induced higher expression of SNAI2, which also promoted TβRII expression. Therefore, the sustained activation levels of both Smad and non-Smad pathways were gradually increased after prolonged stimulation with TGF-β1/H₂O₂/LPS. Consistent with the activation pattern of signaling pathways, the invasive capacity and anoikis-resistance of non-invasive breast cancer cells were gradually increased after prolonged stimulation with TGF-β1/H₂O₂/LPS. The metastatic potential induced by TGF-β1/H₂O₂/LPS was sufficient for tumor cells to extravasate and form metastatic foci in an experimental metastasis model in nude mice. The findings in this study suggested that the enhanced signaling is required for inducing higher metastatic capacity of tumor cells, and that targeting one of stimuli or signaling pathways might be potential approach in comprehensive strategy for tumor therapy.

Trauma-associated human neutrophil alterations revealed by comparative proteomics profiling

PURPOSE

Polymorphonuclear neutrophils (PMNs) play an important role in mediating the innate immune response after severe traumatic injury; however, the cellular proteome response to traumatic condition is still largely unknown.

EXPERIMENTAL DESIGN

We applied 2D-LC-MS/MS-based shotgun proteomics to perform comparative proteome profiling of human PMNs from severe trauma patients and healthy controls.

RESULTS

A total of 197 out of ~2500 proteins (being identified with at least two peptides) were observed with significant abundance changes following the injury. The proteomics data were further compared with transcriptomics data for the same genes obtained from an independent patient cohort. The comparison showed that the protein abundance changes for the majority of proteins were consistent with the mRNA abundance changes in terms of directions of changes. Moreover, increased protein secretion was suggested as one of the mechanisms contributing to the observed discrepancy between protein and mRNA abundance changes. Functional analyses of the altered proteins showed that many of these proteins were involved in immune response, protein biosynthesis, protein transport, NRF2-mediated oxidative stress response, the ubiquitin-proteasome system, and apoptosis pathways.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data suggest increased neutrophil activation and inhibited neutrophil apoptosis in response to trauma. The study not only reveals an overall picture of functional neutrophil response to trauma at the proteome level, but also provides a rich proteomics data resource of trauma-associated changes in the neutrophil that will be valuable for further studies of the functions of individual proteins in PMNs.

Targeting tumor metastasis by regulating Nm23 gene expression

The Nm23 gene is a metastatic suppressor identified in a melanoma cell line and expressed in different tumors where their levels of expression are associated with reduced or increased metastatic potential. Nm23 is one of the over 20 metastasis suppressor genes (MSGs) confirmed in vivo. It is highly conserved from yeast to human, implying a critical developmental function. Tumors with alteration of the p53 gene and reduced expression of the Nm23 gene are more prone to metastasis. Nm23-H1 has 3'-5' exonuclease activity. This review focuses on the role of Nm23 in cancer progression and also a potential novel target for cancer therapy.

nm23-H1 is a negative regulator of TGF-β1-dependent induction of epithelial-mesenchymal transition

Members of transforming growth factor-β(TGF-β) family are the main inducers of epithelial-mesenchymal transition (EMT) during embryogenesis and cancer pathogenesis. However, a significant crosstalk between TGF-β and other signals occurs during the induction of EMT. nm23-H1 was the first metastasis suppressor gene to be identified on the basis of an inverse relationship between nm23-H1 expression and metastasis stage. Despite extensive studies, the mechanism underlying its ability to suppress metastasis is far from elucidated. We demonstrated here that the nm23-H1 negatively regulated TGF-β1-dependent induction of EMT in non-aggressive lung cancer cell line. nm23-H1 knockdown significantly enhanced TGF-β1-induced suppression of epithelial marker E-cadherin and upregulation of mesenchymal markers β-catenin and fibronectin. The invasive and migratory potential of lung cancer cells upon TGF-β1 treatment was also markedly enhanced by nm23-H1 knockdown. On the other hand, the effect of nm23-H1 depletion on TGF-β1-induced EMT was reversed by ectopic re-expression of shRNA-resistant nm23-H1 protein. Furthermore, TGF-β1-induced EMT potentiated by nm23-H1 depletion was partially dependent on transcriptional factor Snail expression. Finally, we found Src kinase is involved in regulation of TGF-β1-induced EMT by nm23-H1. Our results suggest a means of restoring nm23-H1 to suppress TGF-β1-induced EMT that may exploited therapeutically for the management of metastasis diseases.

Murine protein serine-threonine kinase 38 activates p53 function through Ser15 phosphorylation

Murine protein serine-threonine kinase 38 (MPK38) is a member of the AMP-activated protein kinase-related serine/threonine kinase family. In this study, we show that MPK38 physically associates with p53 via the carboxyl-terminal domain of MPK38 and the central DNA-binding domain of p53. This interaction is increased by 5-fluorouracil or doxorubicin treatment and is responsible for Ser(15) phosphorylation of p53. Ectopic expression of wild-type Mpk38, but not kinase-dead Mpk38, stimulates p53-mediated transcription in a dose-dependent manner and up-regulates p53 targets, including p53, p21, MDM2, and BAX. Consistently, knockdown of MPK38 shows an opposite trend, inhibiting p53-mediated transcription. MPK38 functionally enhances p53-mediated apoptosis and cell cycle arrest in a kinase-dependent manner by stimulating p53 nuclear translocation. We also demonstrate that MPK38-mediated p53 activation is induced by removing MDM2, a negative regulator of p53, from the p53-MDM2 complex as well as by stabilization of interaction between p53 and its positive regulators, including NM23-H1, serine/threonine kinase receptor-associated protein, and 14-3-3. This leads to the enhancement of p53 stability. Together, these results suggest that MPK38 may act as a novel regulator for promoting p53 activity through direct phosphorylation of p53 at Ser(15).

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.

Positive regulation of apoptosis signal-regulating kinase 1 signaling by ZPR9 protein, a zinc finger protein

A zinc finger protein, ZPR9, has been identified as a physiological substrate of murine protein serine/threonine kinase 38 (MPK38), which is involved in various cellular responses, including the cell cycle, apoptosis, embryonic development, and oncogenesis. Here, ZPR9 was found to physically interact with apoptosis signal-regulating kinase 1 (ASK1) through a disulfide linkage involving Cys(1351) and Cys(1360) of ASK1 and Cys(305) and Cys(308) of ZPR9. ASK1 directly phosphorylated ZPR9 at Ser(314) and Thr(318), suggesting that ZPR9 can act as an ASK1 substrate. Ectopic expression of wild-type ZPR9, but not an S314A/T318A mutant, stimulated ASK1 kinase activity and positively regulated ASK1-mediated signaling to both JNK and p38 kinases by destabilizing complex formation between ASK1 and its negative regulators, Trx and 14-3-3, or by increasing complex formation between ASK1 and its substrate MKK3. ZPR9 functionally stimulated ASK1-induced AP-1 transcriptional activity as well as H(2)O(2)-mediated apoptosis in a phosphorylation-dependent manner. ASK1-mediated phosphorylation of ZPR9 at Ser(314) and Thr(318) was also responsible for ZPR9-induced apoptosis. Moreover, ZPR9 inhibited PDK1-mediated signaling through ASK1 activation. These results suggest that ZPR9 functions as a novel positive regulator of ASK1.

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.

Learning about the functions of NME/NM23: lessons from knockout mice to silencing strategies

The human NME gene family (also known as NM23) comprises ten genes that are involved in diverse physiological and pathological processes including proliferation, differentiation, development, ciliary functions, and metastasis. For the moment, only the NME1, NME2, and NME7 genes have been inactivated in transgenic knockout mice, as well as a double NME1-NME2 gene knockout. Mice lacking NME1 or NME2 grow to adulthood without health problems, although NME1 (-/-) mice have modest growth retardation. Double knockout NME1 (-/-)-NME2 (-/-) mice, by contrast, are highly hypotrophic and die at birth from profound anemia due to impaired erythroblast development. Evidence for a metastasis suppressor function of NME1 in vivo comes from crossing NME1 (-/-) mice with mice prone to develop hepatocellular carcinoma; the double transgenic mice present a higher incidence of lung metastases. Silencing of NME1 by siRNA interference has confirmed this function by conferring a "metastatic phenotype" on non-invasive human epithelial cancer cell lines. This function is specific to NME1 and is not observed when the NME2 is silenced. The data indicate that NME1 loss is causally involved at the early stages of the metastatic cascade. NME2 (-/-) mice and NME2 silencing experiments reveal a specific role of NME2 in activation of heterotrimeric G proteins and of KCa3.1 channel in T cells, pointing to a role of NME2 as a histidine phosphotransferase. Regarding NME7, consistent with its expression in axonemal structures, NME7 (-/-) mice present lesions similar to primary ciliary dyskinesia. This review summarizes the recent data obtained by knockout and silencing of NME/NM23 genes that provide mechanistic insights into their respective roles in physiology and pathology.

STRAP regulates c-Jun ubiquitin-mediated proteolysis and cellular proliferation

STRAP is a ubiquitous WD40 protein that has been implicated in tumorigenesis. Previous studies suggest that STRAP imparts oncogenic characteristics to cells by promoting ERK and pRb phosphorylation. While these findings suggest that STRAP can activate mitogenic signaling pathways, the effects of STRAP on other MAPK pathways have not been investigated. Herein, we report that STRAP regulates the expression of the c-Jun proto-oncogene in mouse embryonic fibroblasts. Loss of STRAP expression results in reduced phospho-c-Jun and total c-Jun but does not significantly reduce the level of two other early response genes, c-Myc and c-Fos. STRAP knockout also decreases expression of the AP-1 target gene, cyclin D1, which is accompanied by a reduction in cell growth. No significant differences in JNK activity or basal c-Jun mRNA levels were observed between wild type and STRAP null fibroblasts. However, proteasomal inhibition markedly increases c-Jun expression in STRAP knockout MEFs and STRAP over-expression decreases the ubiquitylation of c-Jun in 293T cells. Loss of STRAP accelerates c-Jun turnover in fibroblasts and ectopic over-expression of STRAP in STRAP null fibroblasts increases c-Jun expression. Collectively, our findings indicate that STRAP regulates c-Jun stability by decreasing the ubiquitylation and proteosomal degradation of c-Jun.

TGF-beta-dependent and -independent roles of STRAP in cancer

The serine-threonine kinase receptor-associated protein (STRAP) was initially identified as a putative inhibitor of the canonical TGF-beta signaling pathway. Because the Smad-dependent TGF-beta pathway negatively regulates cellular growth, early functional studies suggested that STRAP behaves as an oncogene. Indeed, a correlation between STRAP overexpression and various cancers has been identified. With the emergence of new studies on the biological function of STRAP, it is becoming clear that STRAP regulates several distinct cellular processes and modulates multiple signaling pathways. While STRAP itself does not possess enzymatic activity, it appears that STRAP influences biological processes through associations with cellular proteins. In this review, we will describe the TGF-beta-dependent and -independent functions of STRAP and provide a context for the significance of STRAP activity in the development of cancer.

Implication of metastasis suppressor NM23-H1 in maintaining adherens junctions and limiting the invasive potential of human cancer cells

Loss of NM23-H1 expression correlates with the degree of metastasis and with unfavorable clinical prognosis in several types of human carcinoma. However, the mechanistic basis for the metastasis suppressor function of NM23-H1 is obscure. We silenced NM23-H1 expression in human hepatoma and colon carcinoma cells and methodologically investigated effects on cell-cell adhesion, migration, invasion, and signaling linked to cancer progression. NM23-H1 silencing disrupted cell-cell adhesion mediated by E-cadherin, resulting in β-catenin nuclear translocation and T-cell factor/lymphoid-enhancing factor-1 transactivation. Further, NM23-H1 silencing promoted cellular scattering, motility, and extracellular matrix invasion by promoting invadopodia formation and upregulating several matrix metalloproteinases (MMP), including membrane type 1 MMP. In contrast, silencing the related NM23-H2 gene was ineffective at promoting invasion. NM23-H1 silencing activated proinvasive signaling pathways involving Rac1, mitogen-activated protein kinases, phosphatidylinositol 3-kinase (PI3K)/Akt, and src kinase. Conversely, NM23-H1 was dispensable for cancer cell proliferation in vitro and liver regeneration in NM23-M1 null mice, instead inducing cellular resistance to chemotherapeutic drugs in vitro. Analysis of NM23-H1 expression in clinical specimens revealed high expression in premalignant lesions (liver cirrhosis and colon adenoma) and the central body of primary liver or colon tumors, but downregulation at the invasive front of tumors. Our findings reveal that NM23-H1 is critical for control of cell-cell adhesion and cell migration at early stages of the invasive program in epithelial cancers, orchestrating a barrier against conversion of in situ carcinoma into invasive malignancy.

Murine protein serine/threonine kinase 38 stimulates TGF-beta signaling in a kinase-dependent manner via direct phosphorylation of Smad proteins

The present study demonstrated that murine protein serine/threonine kinase 38 (MPK38) coimmunoprecipitates with Smad proteins (Smad2, -3, -4, and -7) and that this association is mediated by the catalytic kinase domain of MPK38. The association between MPK38 and Smad2, -3, and -4 was significantly increased by TGF-β or ASK1 signals, whereas these signals decreased association of MPK38 with Smad7. MPK38 stimulated TGF-β-induced transcription required for TGF-β-mediated biological functions, such as apoptosis and cell growth arrest, in a kinase-dependent manner. Knockdown of endogenous MPK38 showed an opposite effect, inhibiting TGF-β signaling. MPK38-mediated phosphorylation of Smad proteins (Ser(245) of Smad2, Ser(204) of Smad3, Ser(343) of Smad4, and Thr(96) of Smad7) was also found to be crucial to the positive regulation of TGF-β signaling induced by MPK38. In addition, MPK38 enhanced nuclear translocation of Smad3, as well as redistribution of Smad7 from the nucleus to the cytoplasm, in response to TGF-β. Together, these results indicate that MPK38 functions as a stimulator of TGF-β signaling through direct interaction with and phosphorylation of Smad proteins.

MMP28 gene expression is regulated by Sp1 transcription factor acetylation

MMP-28 (epilysin) is a recently cloned member of the MMP (matrix metalloproteinase) family. It is highly expressed in the skin by keratinocytes, the developing and regenerating nervous system and a number of other normal human tissues, as well as a number of carcinomas. The MMP28 promoter has previously been cloned and characterized identifying a conserved GT-box that binds Sp1/Sp3 (specificity proteins 1 and 3) proteins and is essential for the basal expression of the gene. The present study demonstrates that MMP28 expression is induced by HDAC (histone deacetylase) inhibitors and that this effect is mediated through the GT-box. Transient transfection assays have shown that the induction of MMP28 expression by the HDAC inhibitior TSA (trichostatin A) is mediated via Sp1 at the GT-box. Immunoprecipitation experiments have shown that the acetylation of Sp1 and Sp3 is increased by TSA treatment; however, no effect on DNA binding was observed. Histone acetyltransferases such as p300 and P/CAF [p300/CREB (cAMP-response-element-binding protein)-binding protein-associated factor] increased induction of the MMP28 promoter by Sp1. Knockdown of HDAC1 using siRNA (small interfering RNA) also induces the MMP28 promoter. Oligonucleotide pulldown identified STRAP (serine/threonine kinase receptor-associated protein) as a further protein recruited to the MMP28 promoter and acting functionally with Sp1.