Modulation of differentiation-related gene 1 expression by cell cycle blocker mimosine, revealed by proteomic analysis

Patient-driven discovery of CCN1 to rescue cutaneous wound healing in diabetes via the intracellular EIF3A/CCN1/ATG7 signaling by nanoparticle-enabled delivery

Diabetic ulcers (DUs), a devastating complication of diabetes, are intractable for limited effective interventions in clinic. Based on the clinical samples and bioinformatic analysis, we found lower level of CCN1 in DU individuals. Considering the accelerated proliferation effect in keratinocytes, we propose the therapeutic role of CCN1 supplementation in DU microenvironment. To address the challenge of rapid degradation of CCN1 in protease-rich diabetic healing condition, we fabricated a nanoformulation of CCN1 (CCN1-NP), which protected CCN1 from degradation and significantly raised CCN1 intracellular delivery efficiency to 6.2-fold. The results showed that the intracellular CCN1 exhibited a greater anti-inflammatory and proliferative/migratory activities once the extracellular signal of CCN1 was blocked in vitro. The nanoformulation unveils a new mechanism that CCN1 delivered into cells interacted with Eukaryotic translation initiation factor 3 subunit A (EIF3A) to downregulate autophagy-related 7 (ATG7). Furthermore, topical application of CCN1-NP had profound curative effects on delayed wound healing in diabetes both in vitro and in vivo. Our results illustrate a novel mechanism of intracellular EIF3A/CCN1/ATG7 axis triggered by nanoformulation and the therapeutic potential of CCN1-NP for DU management.

Bi-allelic variants in DOHH, catalyzing the last step of hypusine biosynthesis, are associated with a neurodevelopmental disorder

Deoxyhypusine hydroxylase (DOHH) is the enzyme catalyzing the second step in the post-translational synthesis of hypusine [N^ε-(4-amino-2-hydroxybutyl)lysine] in the eukaryotic initiation factor 5A (eIF5A). Hypusine is formed exclusively in eIF5A by two sequential enzymatic steps catalyzed by deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Hypusinated eIF5A is essential for translation and cell proliferation in eukaryotes, and all three genes encoding eIF5A, DHPS, and DOHH are highly conserved throughout eukaryotes. Pathogenic variants affecting either DHPS or EIF5A have been previously associated with neurodevelopmental disorders. Using trio exome sequencing, we identified rare bi-allelic pathogenic missense and truncating DOHH variants segregating with disease in five affected individuals from four unrelated families. The DOHH variants are associated with a neurodevelopmental phenotype that is similar to phenotypes caused by DHPS or EIF5A variants and includes global developmental delay, intellectual disability, facial dysmorphism, and microcephaly. A two-dimensional gel analyses revealed the accumulation of deoxyhypusine-containing eIF5A [eIF5A(Dhp)] and a reduction in the hypusinated eIF5A in fibroblasts derived from affected individuals, providing biochemical evidence for deficiency of DOHH activity in cells carrying the bi-allelic DOHH variants. Our data suggest that rare bi-allelic variants in DOHH result in reduced enzyme activity, limit the hypusination of eIF5A, and thereby lead to a neurodevelopmental disorder.

Knockdown of eIF3a attenuated cell growth in K1 human thyroid cancer cells

BACKGROUND

In ribosome establishment and the initiation of translation, eukaryotic translation initiation factor (eIF) 3a is a pivotal functional subunit of the eIF3 complex. In various cancer types, abnormal eIF3a expression plays an important role in tumorigenesis.

OBJECTIVE

We aimed to explore the role of eIF3a in human thyroid cancer (TC).

MATERIAL AND METHODS

The expression of eIF3a was determined in TC tissues by qRT-PCR and immunohistochemistry (IHC) assay, respectively. In addition, the expression of eIF3a in K1 and BCPAP cells were detected by qRT-PCR. Cell proliferation, cell cycle, and cell apoptosis were assessed after eIF3a knockdown in K1 in cell line.

RESULTS

The expression of eIF3a mRNA was high in TC tissues and cancer cell lines. Moreover, eIF3a expression in TC tissues indicated that high eIF3a level was associated with tumor grade. In addition, eIF3a knockdown resulted in a significantly decrease in cell proliferation and increased the apoptosis of K1 cells. Cell cycle was arrested in both the S and G2/M phase. The levels of phosphorylated ERK1/2 and surviving were decreased after eIF3a knockdown.

CONCLUSION

Our study suggested that eIF3a contributed to TC cell proliferation. It may be a promising target for gene therapy in human thyroid cancer.

eIF3a Regulation of NHEJ Repair Protein Synthesis and Cellular Response to Ionizing Radiation

Translation initiation in protein synthesis regulated by eukaryotic initiation factors (eIFs) is a crucial step in controlling gene expression. eIF3a has been shown to regulate protein synthesis and cellular response to treatments by anticancer agents including cisplatin by regulating nucleotide excision repair. In this study, we tested the hypothesis that eIF3a regulates the synthesis of proteins important for the repair of double-strand DNA breaks induced by ionizing radiation (IR). We found that eIF3a upregulation sensitized cellular response to IR while its downregulation caused resistance to IR. eIF3a increases IR-induced DNA damages and decreases non-homologous end joining (NHEJ) activity by suppressing the synthesis of NHEJ repair proteins. Furthermore, analysis of existing patient database shows that eIF3a expression associates with better overall survival of breast, gastric, lung, and ovarian cancer patients. These findings together suggest that eIF3a plays an important role in cellular response to DNA-damaging treatments by regulating the synthesis of DNA repair proteins and, thus, eIIF3a likely contributes to the outcome of cancer patients treated with DNA-damaging strategies including IR.

Molecular characterization of mimosinase and cystathionine β-lyase in the Mimosoideae subfamily member Mimosa pudica

Mimosinase degrades the non-protein amino acid mimosine and is thought to have evolved from cystathionine β-lyase (CBL) via gene duplication. However, no study has, to date, compared the molecular characteristics of mimosinase and CBL. We therefore cloned mimosinase and CBL from the Mimosoideae subfamily member Mimosa pudica (Mp) and explored the molecular relationship between mimosinase and CBL for the first time. The recombinant Mp mimosinase degraded both mimosine and cystathionine with a much higher turnover number (k_cat) for mimosine compared with cystathionine, and Mp CBL utilized only cystathionine as a substrate. The critical residues implicated in the substrate binding of Arabidopsis thaliana CBL (Tyr-127, Arg-129, Tyr-181, and Arg-440) were highly conserved in both Mp mimosinase and CBL. However, homology modeling and molecular simulation of these enzymes predicted variations in the residues that interact with substrates. A mutation experiment on Mp mimosinase revealed that the disruption of a disulfide bond in the vicinity of the pyridoxal-5'-phosphate domain increased the enzyme's preference toward cystathionine. Treatment of Mp mimosinase with a disulfide-cleavage agent also decreased mimosinase activity. Furthermore, mutation near the conserved binding residue altered the substrate preference between mimosine and cystathionine. Molecular dynamics simulations of Mp mimosinase suggested a closer coordination of the residues that interact with mimosine at the active site compared with cystathionine, indicating a more compact pocket size for mimosine degradation. This study thus may provide new insights into the molecular diversification of CBL, a C-S lyase, into the C-N lyase mimosinase in the Mimosoideae subfamily.

Role of eIF3a in 4-amino-2-trifluoromethyl-phenyl retinate-induced cell differentiation in human chronic myeloid leukemia K562 cells

4-amino-2-trifluoromethyl-phenyl retinate (ATPR), a novel all-trans retinoic acid (ATRA) derivative designed and synthesized by our team, has been demonstrated its anti-tumor effect through inducing differentiation and inhibiting proliferation. Eukaryotic initiation factor 3a (eIF3a) plays a critical role in affecting tumor cell proliferation and differentiation. However, whether eIF3a is implicated in chronic myeloid leukemia cells differentiation remains unclear. Our results demonstrated that eIF3a could be suppressed by ATPR in K562 cells. The results also confirmed that ATPR could arrest cell cycle in G0/G1 phase and induced differentiation. Moreover, over-expression of eIF3a promoted not only protein expression of c-myc and cyclin D1, but also prevented the expression of p-Raf-1, p-ERK and the myeloid differentiation markers CD11b and CD14 and had an influence on inducing the morphologic mature. However, silencing eIF3a expression by small interfering RNA could have an adverse effect on K562 cells. In addition, PD98059 (a MEK inhibitor) could block cell differentiation of CML cells and contributed to the expression of c-myc and cyclin D1. In conclusion, these results indicated that eIF3a played an important role in ATPR-induced cell differentiation in K562 cells, its mechanism might be related to its ability in regulating the activation of ERK1/2 signaling pathway in vitro.

Histone Deacetylase Inhibition Restores Expression of Hypoxia-Inducible Protein NDRG1 in Pancreatic Cancer

OBJECTIVES

N-myc downstream-regulated gene-1 (NDRG1) is a hypoxia-inducible and differentiation-related protein and candidate biomarker in pancreatic cancer. As NDRG1 expression is lost in high-grade tumors, the effects of the differentiating histone deacetylase inhibitor trichostatin A (TSA) were examined in human pancreatic cancer cell lines representing different tumor grades.

METHODS

PANC-1 (poorly differentiated) and Capan-1 (moderately to well-differentiated) cells were treated with TSA. Effects were assessed in vitro by microscopic analysis, colorimetric assays, cell counts, real-time polymerase chain reaction, and Western blotting.

RESULTS

Treatment of PANC-1 cells over 4 days with 0.5 μM TSA restored cellular differentiation, inhibited proliferation, and enhanced p21 protein expression. Trichostatin A upregulated NDRG1 mRNA and protein levels under normoxia from day 1 and by 6-fold by day 4 (P < 0.01 at all time points). After 24 hours under hypoxia, NDRG1 expression was further increased in differentiated cells (P < 0.01). Favorable changes were identified in the expression of other hypoxia-regulated genes.

CONCLUSIONS

Histone deacetylase inhibitors offer a potential novel epidrug approach for pancreatic cancer by reversing the undifferentiated phenotype and allowing patients to overcome resistance and better respond to conventional cytotoxic treatments.

Eukaryotic Translation Initiation Factor 3a (eIF3a) Promotes Cell Proliferation and Motility in Pancreatic Cancer

Identifying a target molecule that is crucially involved in pancreatic tumor growth and metastasis is necessary in developing an effective treatment. The study aimed to investigate the role of the eukaryotic translation initiation factor 3a (eIF3a) in the cell proliferation and motility in pancreatic cancer. Our data showed that the expression of eIF3a was upregulated in pancreatic ductal adenocarcinoma as compared with its expression in normal pancreatic tissues. Knockdown of eIF3a by a specific shRNA caused significant decreases in cell proliferation and clonogenic abilities in pancreatic cancer SW1990 and Capan-1 cells. Consistently, the pancreatic cancer cell growth rates were also impaired in xenotransplanted mice. Moreover, wound-healing assay showed that depletion of eIF3a significantly slowed down the wound recovery processes in SW1990 and Capan-1 cells. Transwell migration and invasion assays further showed that cell migration and invasion abilities were significantly inhibited by knockdown of eIF3a in SW1990 and Capan-1 cells. Statistical analysis of eIF3a expression in 140 cases of pancreatic ductal adenocarcinoma samples revealed that eIF3a expression was significantly associated with tumor metastasis and TNM staging. These analyses suggest that eIF3a contributes to cell proliferation and motility in pancreatic ductal adenocarcinoma.

The Chemistry and Biological Activities of Mimosine: A Review

Mimosine [β-[N-(3-hydroxy-4-oxypyridyl)]-α-aminopropionic acid] is a non-protein amino acid found in the members of Mimosoideae family. There are a considerable number of reports available on the chemistry, methods for estimation, biosynthesis, regulation, and degradation of this secondary metabolite. On the other hand, over the past years of active research, mimosine has been found to have various biological activities such as anti-cancer, antiinflammation, anti-fibrosis, anti-influenza, anti-virus, herbicidal and insecticidal activities, and others. Mimosine is a leading compound of interest for use in the development of RAC/CDC42-activated kinase 1 (PAK1)-specific inhibitors for the treatment of various diseases/disorders, because PAK1 is not essential for the growth of normal cells. Interestingly, the new roles of mimosine in malignant glioma treatment, regenerative dentistry, and phytoremediation are being emerged. These identified properties indicate an exciting future for this amino acid. The present review is focused on the chemistry and recognized biological activities of mimosine in an attempt to draw a link between these two characteristics. Copyright © 2016 John Wiley & Sons, Ltd.

The hypusine cascade promotes cancer progression and metastasis through the regulation of RhoA in squamous cell carcinoma

Metastasis is a critical factor contributing to poor prognosis in cancer, but the underlying mechanisms of metastasis are still poorly understood. We established a highly metastatic cell subline (HOC313-LM) derived from an oral squamous cell carcinoma cell line (HOC313) for uncovering the mechanisms of metastasis, and identified deoxyhypusine synthase (DHPS) as a metastasis-associated gene within the specific amplification at 19p13.2-p13.13 in HOC313-LM. DHPS-mediated hypusine-modification of eukaryotic translation factor 5A facilitated the translation of RhoA, resulting in the activation of the RhoA signaling pathway and leading to not only increased cell motility, invasion and metastasis of cancer cells in vitro, but also increased tumor growth in vivo. Moreover, the use of N1-Guanyl-1,7-diaminoheptane, a DHPS inhibitor, resulted in a significant decrease in tumor formation in vivo. In patients with esophageal squamous cell carcinoma (ESCC), overexpression of DHPS in ESCC tumors was significantly associated with worse recurrence-free survival, and correlated with distant metastasis. The elucidation of these molecular mechanisms within the hypusine cascade suggests opportunities for novel therapeutic targets in SCC.

Activity of aaptamine and two derivatives, demethyloxyaaptamine and isoaaptamine, in cisplatin-resistant germ cell cancer

We analyzed the effects of all three marine alkaloids aaptamine, demethyloxyaaptamine and isoaaptamine in NT2-R, a cisplatin-resistant subline of the human embryonal carcinoma cell line NT2. All aaptamines were found to be equally effective in both cell lines, excluding cross-resistance between aaptamines and cisplatin in vitro. At the inhibitory concentration (IC50), aaptamine exerted an antiproliferative effect, whereas demethyloxyaaptamine and isoaaptamine were strong inducers of apoptosis. We analyzed the changes in the proteome of NT2-R cells treated with these compounds. 16-22 proteins were found to be significantly altered, of which several were validated by Western blotting and two-dimensional Western blotting analysis. Changes in the proteome pattern frequently resulted from post-transcriptional protein modifications, i.e. phosphorylation or hypusination in the case of eIF5A. Although the lists of altered proteins were heterogeneous and compound-specific, gene ontology analyses identified rather similar profiles regarding the affected molecular functions. Ingenuity pathway analysis by IPA put the following factors in a central position of the hypothetical networks: myc and p53 for aaptamine; tumor necrosis factor (TNF) for demethyloxyaaptamine; and all three, myc, p53, and TNF for isoaaptamine. Our results represent an important step towards a better understanding of the molecular basis underlying the observed bioactivity of these promising marine compounds.

BIOLOGICAL SIGNIFICANCE

We characterized the mode of action of three aaptamines, marine natural compound with anti-tumor activity, using a functional proteomics approach and the cisplatin-resistant pluripotent human embryonal carcinoma cell line NT2-R. The manuscript is of particular scientific interest, as we could reveal the similarities and differences of the modes of action. Furthermore, we were able to identify several new targets of these promising compounds. We found hypusination of eIF5A to be a prominent feature exclusively of aaptamine treatment, as this was not observed upon treatment with demethyloxyaaptamine or isoaaptamine. Our results are a step towards unraveling the mode of action of these interesting compounds.

Molecular functions of the iron-regulated metastasis suppressor, NDRG1, and its potential as a molecular target for cancer therapy

N-myc down-regulated gene 1 (NDRG1) is a known metastasis suppressor in multiple cancers, being also involved in embryogenesis and development, cell growth and differentiation, lipid biosynthesis and myelination, stress responses and immunity. In addition to its primary role as a metastasis suppressor, NDRG1 can also influence other stages of carcinogenesis, namely angiogenesis and primary tumour growth. NDRG1 is regulated by multiple effectors in normal and neoplastic cells, including N-myc, histone acetylation, hypoxia, cellular iron levels and intracellular calcium. Further, studies have found that NDRG1 is up-regulated in neoplastic cells after treatment with novel iron chelators, which are a promising therapy for effective cancer management. Although the pathways by which NDRG1 exerts its functions in cancers have been documented, the relationship between the molecular structure of this protein and its functions remains unclear. In fact, recent studies suggest that, in certain cancers, NDRG1 is post-translationally modified, possibly by the activity of endogenous trypsins, leading to a subsequent alteration in its metastasis suppressor activity. This review describes the role of this important metastasis suppressor and discusses interesting unresolved issues regarding this protein.

Spectrin domain of eukaryotic initiation factor 3a is the docking site for formation of the a:b:i:g subcomplex

eIF3a (eukaryotic translation initiation factor 3a), one of the core subunits of the eIF3 complex, has been implicated in regulating translation of different mRNAs and in tumorigenesis. A subcomplex consisting of eIF3a, eIF3b, eIF3g, and eIF3i (eIF3(a:b:i:g)) has also been identified. However, how eIF3a participates in translational regulation and in formation of the eIF3(a:b:i:g) subcomplex remain to be solved. In this study, we used the tandem affinity purification approach in combination with tandem MS/MS and identified the spectrin domain of eIF3a as the docking site for the formation of eIF3(a:b:i:g) subcomplex. Although eIF3b and eIF3i bind concurrently to the spectrin domain of eIF3a within ∼10-15 amino acids apart, eIF3g binds to eIF3a indirectly via binding to the carboxyl-terminal domain of eIF3b. The binding of eIF3b to the spectrin domain of eIF3a occurs in its RNA recognition motif domain where eIF3j also binds in a mutually exclusive manner. Together, we conclude that the spectrin domain of eIF3a is responsible for the formation of eIF3(a:b:i:g) subcomplex and, because of mutually exclusive nature of bindings of eIF3a and eIF3j to eIF3b, different subcomplexes of eIF3 likely exist and may perform noncanonical functions in translational regulation.

Gelsolin induces promonocytic leukemia differentiation accompanied by upregulation of p21CIP1

Tumor suppressor genes have received much attention for their roles in the development of human malignancies. Gelsolin has been found to be down-regulated in several types of human cancers, including leukemias. It is, however, expressed in macrophages, which are the final differentiation derivatives for the monocytic myeloid lineage, implicating this protein in the differentiation process of such cells. In order to investigate the role of gelsolin in leukaemic cell differentiation, stable clones over-expressing ectopic gelsolin, and a control clone were established from U937 leukaemia cells. Unlike the control cells, both gelsolin-overexpressing clones displayed retarded growth, improved monocytic morphology, increased NADPH and NSE activities, and enhanced surface expression of the β-integrin receptor, CD11b, when compared with the parental U937 cells. Interestingly, RT- PCR and western blot analysis also revealed that gelsolin enhanced p21CIP1 mRNA and protein expression in the overexpressing clones. Moreover, transient transfection with siRNA silencing P21CIP1, but not the control siRNA, resulted in a reduction in monocytic differentiation, accompanied by an increase in proliferation. In conclusion, our work demonstrates that gelsolin, by itself, is capable of inducing monocytic differentiation in U937 leukaemia cells, most probably through p21CIP1 activation.

The iron-regulated metastasis suppressor NDRG1 targets NEDD4L, PTEN, and SMAD4 and inhibits the PI3K and Ras signaling pathways

AIMS

The metastasis suppressor gene, N-myc downstream regulated gene-1 (NDRG1), is negatively correlated with tumor progression in multiple neoplasms, including pancreatic cancer. Moreover, NDRG1 is an iron-regulated gene that is markedly upregulated by cellular iron-depletion using novel antitumor agents such as the chelator, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), in pancreatic cancer cells. However, the exact function(s) of NDRG1 remain to be established and are important to elucidate.

RESULTS

In the current study, using gene-array analysis along with NDRG1 overexpression and silencing, we identified the molecular targets of NDRG1 in three pancreatic cancer cell lines. We demonstrate that NDRG1 upregulates neural precursor cell expressed developmentally downregulated 4-like (NEDD4L) and GLI-similar-3 (GLIS3). Further studies examining the downstream effects of NEDD4L led to the discovery that NDRG1 affects the transforming growth factor-β (TGF-β) pathway, leading to the upregulation of two key tumor suppressor proteins, namely phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and mothers against decapentaplegic homolog-4 (SMAD4). Moreover, NDRG1 inhibited the phosphatidylinositol 3-kinase (PI3K) and Ras oncogenic pathways.

INNOVATION

This study provides significant insights into the mechanisms underlying the antitumor activity of NDRG1. For the first time, a role for NDRG1 is established in regulating the key signaling pathways involved in oncogenesis (TGF-β, PI3K, and Ras pathways).

CONCLUSION

The identified target genes of NDRG1 and their effect on the TGF-β signaling pathway reveal its molecular function in pancreatic cancer and a novel therapeutic avenue.

Deoxyhypusine hydroxylase from Plasmodium vivax, the neglected human malaria parasite: molecular cloning, expression and specific inhibition by the 5-LOX inhibitor zileuton

Primaquine, an 8-aminoquinoline, is the only drug which cures the dormant hypnozoites of persistent liver stages from P. vivax. Increasing resistance needs the discovery of alternative pathways as drug targets to develop novel drug entities. Deoxyhypusine hydroxylase (DOHH) completes hypusine biosynthesis in eukaryotic initiation factor (eIF-5A) which is the only cellular protein known to contain the unusual amino acid hypusine. Modified EIF-5A is important for proliferation of the malaria parasite. Here, we present the first successful cloning and expression of DOHH from P. vivax causing tertiary malaria. The nucleic acid sequence of 1041 bp encodes an open reading frame of 346 amino acids. Histidine tagged expression of P. vivax DOHH detected a protein of 39.01 kDa in E. coli. The DOHH protein from P. vivax shares significant amino acid identity to the simian orthologues from P. knowlesi and P. yoelii strain H. In contrast to P. falciparum only four E-Z-type HEAT-like repeats are present in P. vivax DOHH with different homology to phycocyanin lyase subunits from cyanobacteria and in proteins participating in energy metabolism of Archaea and Halobacteria. However, phycocyanin lyase activity is absent in P. vivax DOHH. The dohh gene is present as a single copy gene and transcribed throughout the whole erythrocytic cycle. Specific inhibition of recombinant P. vivax DOHH is possible by complexing the ferrous iron with zileuton, an inhibitor of mammalian 5-lipoxygenase (5-LOX). Ferrous iron in the active site of 5-LOX is coordinated by three conserved histidines and the carboxylate of isoleucine(673). Zileuton inhibited the P. vivax DOHH protein with an IC50 of 12,5 nmol determined by a relative quantification by GC/MS. By contrast, the human orthologue is only less affected with an IC50 of 90 nmol suggesting a selective iron-complexing strategy for the parasitic enzyme.

N-myc downstream regulated 1 (NDRG1) is regulated by eukaryotic initiation factor 3a (eIF3a) during cellular stress caused by iron depletion

Iron is critical for cellular proliferation and its depletion leads to a suppression of both DNA synthesis and global translation. These observations suggest that iron depletion may trigger a cellular “stress response”. A canonical response of cells to stress is the formation of stress granules, which are dynamic cytoplasmic aggregates containing stalled pre-initiation complexes that function as mRNA triage centers. By differentially prioritizing mRNA translation, stress granules allow for the continued and selective translation of stress response proteins. Although the multi-subunit eukaryotic initiation factor 3 (eIF3) is required for translation initiation, its largest subunit, eIF3a, may not be essential for this activity. Instead, eIF3a is a vital constituent of stress granules and appears to act, in part, by differentially regulating specific mRNAs during iron depletion. Considering this, we investigated eIF3a’s role in modulating iron-regulated genes/proteins that are critically involved in proliferation and metastasis. In this study, eIF3a was down-regulated and recruited into stress granules by iron depletion as well as by the classical stress-inducers, hypoxia and tunicamycin. Iron depletion also increased expression of the metastasis suppressor, N-myc downstream regulated gene-1 (NDRG1), and a known downstream repressed target of eIF3a, namely the cyclin-dependent kinase inhibitor, p27^kip1. To determine if eIF3a regulates NDRG1 expression, eIF3a was inducibly over-expressed or ablated. Importantly, eIF3a positively regulated NDRG1 expression and negatively regulated p27^kip1 expression during iron depletion. This activity of eIF3a could be due to its recruitment to stress granules and/or its ability to differentially regulate mRNA translation during cellular stress. Additionally, eIF3a positively regulated proliferation, but negatively regulated cell motility and invasion, which may be due to the eIF3a-dependent changes in expression of NDRG1 and p27^kip1 observed under these conditions.

Activation of PKCβII by PMA facilitates enhanced epithelial wound repair through increased cell spreading and migration

Rapid repair of epithelial wounds is essential for intestinal homeostasis, and involves cell proliferation and migration, which in turn are mediated by multiple cellular signaling events including PKC activation. PKC isoforms have been implicated in regulating cell proliferation and migration, however, the role of PKCs in intestinal epithelial cell (IEC) wound healing is still not completely understood. In the current work we used phorbol 12-myristate 13-acetate (PMA), a well recognized agonist of classical and non-conventional PKC subfamilies to investigate the effect of PKC activation on IEC wound healing. We found that PMA treatment of wounded IEC monolayers resulted in 5.8±0.7-fold increase in wound closure after 24 hours. The PMA effect was specifically mediated by PKCβII, as its inhibition significantly diminished the PMA-induced increase in wound closure. Furthermore, we show that the PKCβII-mediated increase in IEC wound closure after PMA stimulation was mediated by increased cell spreading/cell migration but not proliferation. Cell migration was mediated by PKCβII dependent actin cytoskeleton reorganization, enhanced formation of lamellipodial extrusions at the leading edge and increased activation of the focal adhesion protein, paxillin. These findings support a role for PKCβII in IEC wound repair and further demonstrate the ability of epithelial cells to migrate as a sheet thereby efficiently covering denuded surfaces to recover the intestinal epithelial barrier.

Dp44mT targets the AKT, TGF-β and ERK pathways via the metastasis suppressor NDRG1 in normal prostate epithelial cells and prostate cancer cells

BACKGROUND

Effective treatment of prostate cancer should be based on targeting interactions between tumour cell signalling pathways and key converging downstream effectors. Here, we determined how the tumourigenic phosphoinositide 3-kinase/protein kinase B (PI3K/AKT), tumour-suppressive phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and transforming growth factor-β (TGF-β) pathways are integrated via the metastasis suppressor, N-myc downstream-regulated gene-1 (NDRG1). Moreover, we assessed how the novel anti-tumour agent, Dp44mT, may target these integrated pathways by increasing NDRG1 expression.

METHODS

Protein expression in Dp44mT-treated normal human prostate epithelial cells and prostate cancer cells (PC-3, DU145) was assessed by western blotting. The role of NDRG1 was examined by transfection using an NDRG1 overexpression vector or shRNA.

RESULTS

Dp44mT increased levels of tumour-suppressive PTEN, and decreased phosphorylation of ERK1/2 and SMAD2L, which are regulated by oncogenic Ras/MAPK signalling. Importantly, the effects of Dp44mT on NDRG1 and p-SMAD2L expression were more marked in prostate cancer cells than normal prostate epithelial cells. This may partly explain the anti-tumour selectivity of these agents. Silencing NDRG1 expression increased phosphorylation of tumourigenic AKT, ERK1/2 and SMAD2L and decreased PTEN levels, whereas NDRG1 overexpression induced the opposite effect. Furthermore, NDRG1 silencing significantly reduced the ability of Dp44mT to suppress p-SMAD2L and p-ERK1/2 levels.

CONCLUSION

NDRG1 has an important role in mediating the tumour-suppressive effects of Dp44mT in prostate cancer via selective targeting of the PI3K/AKT, TGF-β and ERK pathways.

Prognostic significance of NDRG1 expression in oral and oropharyngeal squamous cell carcinoma

Human N-myc downstream-regulated gene 1 (NDRG1) is a metastasis suppressor gene with several potential functions, including cell differentiation, cell cycle regulation and response to hormones, nickel and stress. The purpose of this study was to investigate the immunoexpression of NDRG1 in oral and oropharyngeal squamous cell carcinomas searching for its role in the clinical course of these tumors. We investigated immunohistochemical expression of NDRG1 protein in 412 tissue microarray cores of tumor samples from 103 patients with oral and oropharyngeal squamous cell carcinomas and in 110 paraffin-embedded surgical margin sections. The results showed NDRG1 up-regulation in 101/103 (98.1 %) tumor samples, but no expression in any normal tissue sample. Western blot assays confirmed the immunohistochemical findings, suggesting that lower levels of NDRG1 are associated with a high mortality rate. NDRG1 overexpression was related to long-term specific survival (HR = 0.38; p = 0.009), whereas the presence of lymph-node metastasis showed the opposite association with survival (HR = 2.45; p = 0.013). Our findings reinforce the idea that NDRG1 plays a metastasis suppressor role in oral and oropharyngeal squamous cell carcinomas and may be a useful marker for these tumors.

Human ABCC1 interacts and colocalizes with ATP synthase α, revealed by interactive proteomics analysis

Human ABCC1 is a member of the ATP-binding cassette (ABC) transporter superfamily, and its overexpression has been shown to cause multidrug resistance by active efflux of a wide variety of anticancer drugs. ABCC1 has been shown to exist and possibly function as a homodimer. However, a possible heterocomplex involving ABCC1 has been indicated. In this study, we performed an interactive proteomics study to examine proteins that bind to and form heterocomplexes with ABCC1 using coimmunoprecipitation and tandem mass spectrometry (MS/MS) analyses. We found that ATP synthase α binds to ABCC1 in plasma membranes with a ratio of 2:1. The ATP synthase α binding site in ABCC1 is located in the linker domain at the carboxyl core of ABCC1, and phosphorylation of the linker domain at the protein kinase A site enhances ATP synthase α binding. The interaction between ABCC1 and ATP synthase α in a heterocomplex may indicate a novel function of ABCC1 in regulating extracellular ATP level and purinergic signaling cascade.

L-Mimosine blocks cell proliferation via upregulation of B-cell translocation gene 2 and N-myc downstream regulated gene 1 in prostate carcinoma cells

L-Mimosine, an iron chelator and a prolyl 4-hydroxylase inhibitor, blocks many cancer cells at the late G1 phase. B-cell translocation gene 2 (Btg2) regulates the G1/S transition phases of the cell cycle. N-myc downstream regulated gene 1 (Ndrg1) is a differentiation-inducing gene upregulated by hypoxia. We evaluated the molecular mechanisms of L-mimosine on cell cycle modulation in PC-3 and LNCaP prostate carcinoma cells. The effect of L-mimosine on cell proliferation of prostate carcinoma cells was determined by the [3H]thymidine incorporation and flow cytometry assays. L-Mimosine arrested the cell cycle at the G1 phase in PC-3 cells and at the S phase in LNCaP cells, thus attenuating cell proliferation. Immunoblot assays indicated that hypoxia and L-mimosine stabilized hypoxia-inducible factor-1α (HIF-1α) and induced Btg2 and Ndrg1 protein expression, but downregulated protein levels of cyclin A in both PC-3 and LNCaP cells. L-Mimosine treatment decreased cyclin D1 protein in PC-3 cells, but not in LNCaP cells. Dimethyloxalylglycine, a pan-prolyl hydroxylase inhibitor, also induced Btg2 and Ndrg1 protein expression in LNCaP cells. The transient gene expression assay revealed that L-mimosine treatment or cotransfection with HIF-1α expression vector enhanced the promoter activities of Btg2 and Ndrg1 genes. Knockdown of HIF-1α attenuated the increasing protein levels of both Btg2 and Ndrg1 by hypoxia or L-mimosine in LNCaP cells. Our results indicated that hypoxia and L-mimosine modulated Btg2 and Ndrg1 at the transcriptional level, which is dependent on HIF-1α. L-Mimosine enhanced expression of Btg2 and Ndrg1, which attenuated cell proliferation of the PC-3 and LNCaP prostate carcinoma cells.

N-myc downstream regulated gene1/Cap43 overexpression suppresses tumor growth by hepatic cancer cells through cell cycle arrest at the G0/G1 phase

N-myc downstream regulated gene-1 (NDRG1)/Cap43 regulates tumor growth and metastasis in various carcinomas. In this study we examined whether and how NDRG1/Cap43 modulates tumor growth by human hepatocellular carcinoma (HCC) cells. NDRG1/Cap43 cDNA was used to transfect HCC cell lines (KIM-1), and stable transfectants overexpressing NDRG1/Cap43 (KIM-1/Cap43) were obtained. Cell cycle analysis showed that KIM-1/Cap43 cells were arrested in the G0/G1 phase. Western blot analysis demonstrated an increase in p21 in KIM-1/Cap43 cells in culture under full confluency as compared with KIM-1/Mock. When KIM-1 cells, which are very low in NDRG1/Cap43 expression, were treated with mimosine, a G0/G1 cell cycle blocker, expression of NDRG1/Cap43 was induced in a dose dependent manner, together with p21 induction and CDK4 reduction. In vivo, KIM-1/Cap43 cells showed markedly decreased tumor growth rates compared with those of KIM-1/Mock. Immunohistochemical staining demonstrated markedly higher p21 labeling index in the KIM-1/Cap43 tumor than KIM-1/Mock tumor, and lower CDK4 and Ki-67 labeling index in the KIM-1/Cap43 than KIM-1/Mock. In order to confirm suppressive effects of NDRG1/Cap43, we further established a stable transfectant expressing NDRG1/Cap43 (HAK-1B/Cap43) using another HCC cell line, HAK-1B. Western blot analysis demonstrated an increase in p21 and a decrease in CDK4 in HAK-1B/Cap43 cells in culture under full confluency as compared with HAK-1B/Mock. HAK-1B/Cap43 also showed decreased tumor growth rates as compared with its control counterpart in vivo. NDRG1/Cap43 overexpression thus induced cell cycle arrest at the G0/G1 phase accompanied by increased p21 and decreased CDK4 expression in HCC cells. NDRG1/Cap43 might play a key role in the cell cycle control of G0/G1 in HCC cells.

A protein network-guided screen for cell cycle regulators in Drosophila

Background

Large-scale RNAi-based screens are playing a critical role in defining sets of genes that regulate specific cellular processes. Numerous screens have been completed and in some cases more than one screen has examined the same cellular process, enabling a direct comparison of the genes identified in separate screens. Surprisingly, the overlap observed between the results of similar screens is low, suggesting that RNAi screens have relatively high levels of false positives, false negatives, or both.

Results

We re-examined genes that were identified in two previous RNAi-based cell cycle screens to identify potential false positives and false negatives. We were able to confirm many of the originally observed phenotypes and to reveal many likely false positives. To identify potential false negatives from the previous screens, we used protein interaction networks to select genes for re-screening. We demonstrate cell cycle phenotypes for a significant number of these genes and show that the protein interaction network is an efficient predictor of new cell cycle regulators. Combining our results with the results of the previous screens identified a group of validated, high-confidence cell cycle/cell survival regulators. Examination of the subset of genes from this group that regulate the G1/S cell cycle transition revealed the presence of multiple members of three structurally related protein complexes: the eukaryotic translation initiation factor 3 (eIF3) complex, the COP9 signalosome, and the proteasome lid. Using a combinatorial RNAi approach, we show that while all three of these complexes are required for Cdk2/Cyclin E activity, the eIF3 complex is specifically required for some other step that limits the G1/S cell cycle transition.

Conclusions

Our results show that false positives and false negatives each play a significant role in the lack of overlap that is observed between similar large-scale RNAi-based screens. Our results also show that protein network data can be used to minimize false negatives and false positives and to more efficiently identify comprehensive sets of regulators for a process. Finally, our data provides a high confidence set of genes that are likely to play key roles in regulating the cell cycle or cell survival.

Quantitative proteomics reveals a "poised quiescence" cellular state after triggering the DNA replication origin activation checkpoint

An origin activation checkpoint has recently been discovered in the G1 phase of the mitotic cell cycle, which can be triggered by loss of DNA replication initiation factors such as the Cdc7 kinase. Insufficient levels of Cdc7 activate cell cycle arrest in normal cells, whereas cancer cells appear to lack this checkpoint response, do not arrest, and proceed with an abortive S phase, leading to cell death. The differential response between normal and tumor cells at this checkpoint has led to widespread interest in the development of pharmacological Cdc7 inhibitors as novel anticancer agents. We have used RNAi against Cdc7 in combination with SILAC-based high resolution MS proteomics to investigate the cellular mechanisms underlying the maintenance of the origin activation checkpoint in normal human diploid fibroblasts. Bioinformatics analysis identified clear changes in wide-ranging biological processes including altered cellular energetic flux, moderate stress response, reduced proliferative capacity, and a spatially distributed response across the mitochondria, lysosomes, and the cell surface. These results provide a quantitative overview of the processes involved in maintenance of the arrested state, show that this phenotype involves active rather than passive cellular adaptation, and highlight a diverse set of proteins responsible for cell cycle arrest and ultimately for promotion of cellular survival. We propose that the Cdc7-depleted proteome maintains cellular arrest by initiating a dynamic quiescence-like response and that the complexities of this phenotype will have important implications for the continued development of promising Cdc7-targeted cancer therapies.

The translational regulator eIF3a: the tricky eIF3 subunit!

Regulation of gene expression is a fundamental step in cellular physiology as abnormalities in this process may lead to de-regulated growth and cancer. Translation of mRNA is mainly regulated at the rate-limiting initiation step, where many eukaryotic initiation factors (eIFs) are involved. The largest and most complex initiation factor is eIF3 which plays a role in translational regulation, cell growth and cancer. The largest subunit of eIF3 is eIF3a, although it is not required for the general function of eIF3 in translation initiation. However, eIF3a may play a role as a regulator of a subset of mRNAs and has been demonstrated to regulate the expression of p27(kip1), tyrosinated α-tubulin and ribonucleotide reductase M2 subunit. These molecules have a pivotal role in the regulation of the cell cycle. Moreover, the eIF3a mRNA is ubiquitously expressed in all tissues at different levels and is found elevated in a number of cancer types. eIF3a can modulate the cell cycle and may be a translational regulator for proteins important for entrance into S phase. The expression of eIF3a is decreased in differentiated cells in culture and the suppression of eIF3a expression can reverse the malignant phenotype and change the sensitivity of cells to cell cycle modulators. However, the role of eIF3a in cancer is still unclear. In fact, some studies have identified eIF3a to be involved in cancer development, while other results indicate that it could provide protection against evolution into higher malignancy. Together, these findings highlight the "tricky" and interesting nature of eIF3a.

The unique hypusine modification of eIF5A promotes islet beta cell inflammation and dysfunction in mice

In both type 1 and type 2 diabetes, pancreatic islet dysfunction results in part from cytokine-mediated inflammation. The ubiquitous eukaryotic translation initiation factor 5A (eIF5A), which is the only protein to contain the amino acid hypusine, contributes to the production of proinflammatory cytokines. We therefore investigated whether eIF5A participates in the inflammatory cascade leading to islet dysfunction during the development of diabetes. As described herein, we found that eIF5A regulates iNOS levels and that eIF5A depletion as well as the inhibition of hypusination protects against glucose intolerance in inflammatory mouse models of diabetes. We observed that following knockdown of eIF5A expression, mice were resistant to beta cell loss and the development of hyperglycemia in the low-dose streptozotocin model of diabetes. The depletion of eIF5A led to impaired translation of iNOS-encoding mRNA within the islet. A role for the hypusine residue of eIF5A in islet inflammatory responses was suggested by the observation that inhibition of hypusine synthesis reduced translation of iNOS-encoding mRNA in rodent beta cells and human islets and protected mice against the development of glucose intolerance the low-dose streptozotocin model of diabetes. Further analysis revealed that hypusine is required in part for nuclear export of iNOS-encoding mRNA, a process that involved the export protein exportin1. These observations identify the hypusine modification of eIF5A as a potential therapeutic target for preserving islet function under inflammatory conditions.

Association of luteinizing hormone receptor gene expression with cell cycle progression in granulosa cells

During hormonally induced ovarian follicle growth, granulosa cell proliferation increases and returns to baseline prior to the administration of an ovulatory stimulus. Several key genes appear to follow a similar pattern, including the luteinizing hormone receptor (LHCGR), suggesting an association between cell cycle progression and gene expression. The expression of LHCGR mRNA in granulosa cells isolated from immature rats and treated in culture with FSH increased in a time-dependent manner, whereas administration of the cell cycle inhibitor mimosine completely suppressed expression. Although forskolin was able to induce luteinization in cells treated with mimosine, human chorionic gonadotropin had no effect, indicating the functional loss of LHCGR. The effects of mimosine on cell cycle progression and LHCGR mRNA expression were reversible within 24 h of mimosine removal. Cell cycle inhibition did not alter the stability of LHCGR mRNA, indicating that the primary effect was at the transcriptional level. To determine whether the relationship between LHCGR expression and cell cycle were relevant in vivo, immature rats were given a bolus of PMSG, followed by a second injection of either saline or PMSG 24 h later to augment levels of proliferation. The expression of LHCGR mRNA was elevated in the ovaries of animals receiving a supplement of PMSG. Mimosine also blocked cell cycle progression and LHCGR mRNA expression in macaque granulosa cells isolated following controlled ovarian stimulation cycles and in two different mouse Leydig tumor lines. These data collectively indicate that LHCGR mRNA is expressed as a function of the passage of cells across the G1-S phase boundary.

Overexpression of Cap43 gene in supraglottic laryngeal squamous cell carcinoma

Objective:

This study aimed to determine the expression of the Cap43 gene in supraglottic laryngeal squamous cell carcinoma, and to evaluate any correlation between Cap43 gene expression and tumour-associated macrophage infiltration.

Methods:

Four human head and neck squamous cell carcinoma cell lines were cultured (Hep2, KB, Ca9-22 and HSC-3) and expression of the Cap43 gene was analysed by Western blotting. In addition, paraffin-embedded samples of supraglottic laryngeal squamous cell carcinoma and normal supraglottic laryngeal mucosa from 84 patients were analysed immunohistochemically using antibodies to Cap43 and cluster of differentiation 68 glycoprotein. Patients' clinical status was compared with their immunohistochemical results.

Results:

All four head and neck squamous cell carcinoma cell lines exhibited Cap43 expression. The Hep2, Ca9-22 and HSC-3 cells showed a markedly higher level of Cap43 protein than the KB cells. A statistically significant difference was found in Cap43 expression, comparing different differentiation levels and comparing different metastasis stages, for supraglottic squamous cell carcinoma. The number of tumour-associated macrophages correlated with expression of Cap43, not only in the tumour area (r = 0.3708, p = 0.0005) but also in the peritumour area (r = 0.2847, p = 0.0087).

Conclusion:

In supraglottic laryngeal squamous cell carcinoma, overexpression of the Cap43 gene is associated with tumour differentiation and acts an important suppressive factor in the process of tumour metastasis. The Cap43 gene may be a cancer-specific marker. High expression of the Cap43 gene appeared to correlate with infiltration of tumour-associated macrophages.

Differential genomic and proteomic profiling of glioblastoma cells exposed to terpyridineplatinum(II) complexes

Terpyridineplatinum(II) complexes (TPCs) efficiently inhibit the proliferation of glioblastoma cells in vitro and have been tested successfully in a rodent glioblastoma model. Apart from intercalation with DNA, the major mechanism of action of TPCs is a very potent and specific interaction with the human selenoprotein thioredoxin reductase (TrxR). TrxR plays a crucial role in cellular redox homeostasis and protection against oxidative damage. In many malignant cells the thioredoxin system is upregulated, promoting tumor growth and progression. Thus, the thioredoxin system has been proposed to be an attractive target for cancer therapy. This study gives the first comprehensive overview of the effects of TPCs on the transcriptome and proteome of glioblastoma cells. We reveal that under TPC treatment, mechanisms countersteering TrxR inhibition are activated in parallel to DNA-damage-responsive pathways. TPC pressure results in long-term compensatory upregulation of TrxR expression. In parallel, p53 is activated, leading to a range of regulations typical for cell-cycle-arrested cells such as upregulation of CDKN1A, induction of GADD45, inhibition of eIF5A maturation, and reduced phosphorylation of stathmin. We also show that TPCs induce endoplasmic reticulum stress, as they activate the unfolded protein response. This profiling study provides a thorough insight into the spectrum of cellular events resulting from specific TrxR inhibition and characterizes the TPC mode of action.

The TGF-beta, PI3K/Akt and PTEN pathways: established and proposed biochemical integration in prostate cancer

A key to the development of improved pharmacological treatment strategies for cancer is an understanding of the integration of biochemical pathways involved in both tumorigenesis and cancer suppression. Furthermore, genetic markers that may predict the outcome of targeted pharmacological intervention in an individual are central to patient-focused treatment regimens rather than the traditional 'one size fits all' approach. Prostate cancer is a highly heterogeneous disease in which a patient-tailored care program is a holy grail. This review will describe the evidence that demonstrates the integration of three established pathways: the tumour-suppressive TGF-beta (transforming growth factor-beta) pathway, the tumorigenic PI3K/Akt (phosphoinositide 3-kinase/protein kinase B) pathway and the tumour-suppressive PTEN (phosphatase and tensin homologue deleted on chromosome 10) pathway. It will discuss gene polymorphisms and somatic mutations in relevant genes and highlight novel pharmaceutical agents that target key points in these integrated pathways.

Pharmacological targeting of the integrated protein kinase B, phosphatase and tensin homolog deleted on chromosome 10, and transforming growth factor-beta pathways in prostate cancer

Prostate cancer is a highly heterogenous disease in which a patient-tailored care program is much desired. Central to this goal is the development of novel targeted pharmacological interventions. To develop these treatment strategies, an understanding of the integration of cellular pathways involved in both tumorigenesis and tumor suppression is crucial. Of further interest are the events elicited by drug treatments that exploit the underlying molecular pathology in cancer. This review briefly describes the evidence that suggests integration of three established pathways: the tumorigenic phosphoinositide 3-kinase/protein kinase B (AKT) pathway, the tumor suppressive phosphatase and tensin homolog deleted on chromosome 10 pathway, and the tumor suppressive transforming growth factor-beta pathway. More importantly, we discuss novel pharmaceutical agents that target key points of integration in these three pathways. These new therapeutic strategies include the use of agents that target iron to inhibit proliferation via multiple mechanisms and suppression of AKT by cytosolic phospholipase A(2)-alpha inhibitors.

Eukaryotic translation initiation factor 5A induces apoptosis in colon cancer cells and associates with the nucleus in response to tumour necrosis factor alpha signalling

Eukaryotic translation initiation factor 5A (eIF5A) is thought to function as a nucleocytoplasmic shuttle protein. There are reports of its involvement in cell proliferation, and more recently it has also been implicated in the regulation of apoptosis. In the present study, we examined the effects of eIF5A over-expression on apoptosis and of siRNA-mediated suppression of eIF5A on expression of the tumour suppressor protein, p53. Over-expression of either eIF5A or a mutant of eIF5A incapable of being hypusinated was found to induce apoptosis in colon carcinoma cells. Our results also indicate that eIF5A is required for expression of p53 following the induction of apoptosis by treatment with Actinomycin D. Depiction of eIF5A localization by indirect immunofluorescence has indicated, for the first time, that the protein is rapidly translocated from the cytoplasm to the nucleus by death receptor activation or following treatment with Actinomycin D. These findings collectively indicate that unhypusinated eIF5A may have pro-apoptotic functions and that eIF5A is rapidly translocated to the nucleus following the induction of apoptotic cell death.

Identification of markers for nipple epidermis: changes in expression during pregnancy and lactation

In vertebrates, specific regions of skin crucial for interaction with and manipulation of elements in the environment are characterized by specialized epidermis. Regions of specialized epidermis show distinct patterns of cellular differentiation and express specific keratins that provide an increased ability to withstand mechanical strain. The nipple, which must endure the mechanical strain of nursing, is a type of specialized epidermis. The entire ventral skin of the keratin 14 promoter driven PTHrP mouse provides a model for nipple development. To identify novel markers for this specialized epidermis, we have used two-dimensional (2-D) gels, mass spectrometric protein identification, Western blotting and immunohistochemistry to compare intermediate filament preparations from the nipple-like K14-PTHrP ventral skin to that of wild-type littermates. We identified 64 spots on 2-D gels that were increased in expression in the nipple-like skin of the female K14-PTHrP mouse and 11 spots that were elevated in the wild type. Microsequencing suggested that K17 and epiplakin were among the proteins with the greatest increase in expression in the K14-PTHrP ventral skin. Using Western blots and immunohistochemistry, we evaluated the expression of these proteins as well as K6 in the wild-type nipple, K14-PTHrP ventral skin and wild-type ventral skin. In addition, we found that the expression of K6 was minimally changed in the pregnant and lactating nipple, but the expression of a previously identified marker, K2e, was reduced during lactation. Using a model of the mechanical strain induced by nursing, we found that K2e but not K6 expression was responsive to this condition. The identification of epidermal markers and their expression patterns will provide insight into the cellular differentiation patterns of the nipple and the underlying epidermal-mesenchymal interactions that direct this differentiation.

Piperidones with activity against Plasmodium falciparum

The increasing resistance of the malaria parasites has enforced new strategies of finding new drug targets. We have isolated two genes involved in spermidine metabolism, encoding deoxyhypusine synthase (DHS) and eukaryotic initiation factor 5A (eIF-5A) in the malaria parasites. eIF-5A is activated by the formation of the unusual amino acid hypusine. This process occurs in two steps. DHS transfers an aminobutyl moiety from the triamine spermidine to a specific lysine residue in the eIF-5A precursor protein to form deoxyhypusine. In a second step, deoxyhypusine hydroxylase (DHH), completes hypusine biosynthesis. We used DHH inhibitors, being effective in mammalian cells, to study an antiplasmodicidal effect in Plasmodium falciparum. Experiments with the antifungal drug ciclopiroxolamine, an alpha-hydroxypyridone, and the plant amino acid L: -mimosine, a 4-pyridone, resulted in an antiplasmodial effect in vitro. Using mimosine as a lead structure, alkyl 4-oxo-piperidine 3-carboxylates were found to have the most efficient antiplasmodial effects in vitro and in vivo.