Purification of novel calcium binding proteins from Trypanosoma brucei: properties of 22-, 24- and 38-kilodalton proteins

Translationally controlled tumor protein: the mediator promoting cancer invasion and migration and its potential clinical prospects

Translationally controlled tumor protein (TCTP) is a highly conserved multifunctional protein localized in the cytoplasm and nucleus of eukaryotic cells. It is secreted through exosomes and its degradation is associated with the ubiquitin-proteasome system (UPS), heat shock protein 27 (Hsp27), and chaperone-mediated autophagy (CMA). Its structure contains three α‍-helices and eleven β‍-strands, and features a helical hairpin as its hallmark. TCTP shows a remarkable similarity to the methionine-R-sulfoxide reductase B (MsrB) and mammalian suppressor of Sec4 (Mss4/Dss4) protein families, which exerts guanine nucleotide exchange factor (GEF) activity on small guanosine triphosphatase (GTPase) proteins, suggesting that some functions of TCTP may at least depend on its GEF action. Indeed, TCTP exerts GEF activity on Ras homolog enriched in brain (Rheb) to boost the growth and proliferation of Drosophila cells. TCTP also enhances the expression of cell division control protein 42 homolog (Cdc42) to promote cancer cell invasion and migration. Moreover, TCTP regulates cytoskeleton organization by interacting with actin microfilament (MF) and microtubule (MT) proteins and inducing the epithelial-mesenchymal transition (EMT) process. In essence, TCTP promotes cancer cell movement. It is usually highly expressed in cancerous tissues and thus reduces patient survival; meanwhile, drugs can target TCTP to reduce this effect. In this review, we summarize the mechanisms of TCTP in promoting cancer invasion and migration, and describe the current inhibitory strategy to target TCTP in cancerous diseases.

Expression and purification of a cleavable recombinant fortilin from Escherichia coli for structure activity studies

Complications related to atherosclerosis account for approximately 1 in 4 deaths in the United States and treatment has focused on lowering serum LDL-cholesterol levels with statins. However, approximately 50% of those diagnosed with atherosclerosis have blood cholesterol levels within normal parameters. Human fortilin is an anti-apoptotic protein and a factor in macrophage-mediated atherosclerosis and is hypothesized to protect inflammatory macrophages from apoptosis, leading to subsequent cardiac pathogenesis. Fortilin is unique because it provides a novel drug target for atherosclerosis that goes beyond lowering cholesterol and utilization of a solution nuclear magnetic resonance (NMR) spectroscopy, structure-based drug discovery approach requires milligram quantities of pure, bioactive, recombinant fortilin. Here, we designed expression constructs with different affinity tags and protease cleavage sites to find optimal conditions to obtain the quantity and purity of protein necessary for structure activity relationship studies. Plasmids encoding fortilin with maltose binding protein (MBP), 6-histidine (6His) and glutathione-S-transferase (GST), N- terminal affinity tags were expressed and purified from Escherichia coli (E. coli). Cleavage sites with tobacco etch virus (TEV) protease and human rhinovirus (HRV) 3C protease were assessed. Despite high levels of expression of soluble protein, the fusion constructs were resistant to proteinases without the inclusion of amino acids between the cleavage site and N-terminus. We surveyed constructs with increasing lengths of glycine/serine (GGS) linkers between the cleavage site and fortilin and found that inclusion of at least one GGS insert led to successful protease cleavage and pure fortilin with conserved binding to calcium as measured by NMR.

The translationally controlled tumor protein TCTP is involved in cell cycle progression and heat stress response in the bloodstream form of Trypanosoma brucei

The translationally controlled tumor protein TCTP, is a universally conserved protein that seems to be of essential function in all systems tested so far. TCTP is involved in a multitude of cellular functions including cell cycle control, cell division, apoptosis and many more. The mechanism of how TCTP is involved in most of these functions remains elusive. Here we describe that TCTP is a cytoplasmic protein involved in cell cycle regulation and heat stress response in the bloodstream form of Trypanosoma brucei.

Distinct 3' UTRs regulate the life-cycle-specific expression of two TCTP paralogs in Trypanosoma brucei

The translationally controlled tumor protein (TCTP; also known as TPT1 in mammals) is highly conserved and ubiquitously expressed in eukaryotes. It is involved in growth and development, cell cycle progression, protection against cellular stresses and apoptosis, indicating the multifunctional role of the protein. Here, for the first time, we characterize the expression and function of TCTP in the human and animal pathogen, Trypanosoma brucei. We identified two paralogs (TCTP1 and TCTP2) that are differentially expressed in the life cycle of the parasite. The genes have identical 5′ untranslated regions (UTRs) and almost identical open-reading frames. The 3′UTRs differ substantially in sequence and length, and are sufficient for the exclusive expression of TCTP1 in procyclic- and TCTP2 in bloodstream-form parasites. Furthermore, we characterize which parts of the 3′UTR are needed for TCTP2 mRNA stability. RNAi experiments demonstrate that TCTP1 and TCTP2 expression is essential for normal cell growth in procyclic- and bloodstream-form parasites, respectively. Depletion of TCTP1 in the procyclic form cells leads to aberrant cell and mitochondrial organelle morphology, as well as enlarged, and a reduced number of, acidocalcisomes.

Summary:T. brucei has two TCTP genes that are differentially expressed during the parasite life cycle owing to their different 3′UTRs. TCTP also has a role in regulating cell growth and morphology.

Structural Insights into TCTP and Its Interactions with Ligands and Proteins

The 19-24 kDa Translationally Controlled Tumor Protein (TCTP) is involved in a wide range of molecular interactions with biological and nonbiological partners of various chemical compositions such as proteins, peptides, nucleic acids, carbohydrates, or small molecules. TCTP is therefore an important and versatile binding platform. Many of these protein-protein interactions have been validated, albeit only few received an in-depth structural characterization. In this chapter, we will focus on the structural analysis of TCTP and we will review the available literature regarding its interaction network from a structural perspective.

The Translational Controlled Tumour Protein TCTP: Biological Functions and Regulation

The Translational Controlled Tumour Protein TCTP (gene symbol TPT1, also called P21, P23, Q23, fortilin or histamine-releasing factor, HRF) is a highly conserved protein present in essentially all eukaryotic organisms and involved in many fundamental cell biological and disease processes. It was first discovered about 35 years ago, and it took an extended period of time for its multiple functions to be revealed, and even today we do not yet fully understand all the details. Having witnessed most of this history, in this chapter, I give a brief overview and review the current knowledge on the structure, biological functions, disease involvements and cellular regulation of this protein.TCTP is able to interact with a large number of other proteins and is therefore involved in many core cell biological processes, predominantly in the response to cellular stresses, such as oxidative stress, heat shock, genotoxic stress, imbalance of ion metabolism as well as other conditions. Mechanistically, TCTP acts as an anti-apoptotic protein, and it is involved in DNA-damage repair and in cellular autophagy. Thus, broadly speaking, TCTP can be considered a cytoprotective protein. In addition, TCTP facilitates cell division through stabilising the mitotic spindle and cell growth through modulating growth signalling pathways and through its interaction with the proteosynthetic machinery of the cell. Due to its activities, both as an anti-apoptotic protein and in promoting cell growth and division, TCTP is also essential in the early development of both animals and plants.Apart from its involvement in various biological processes at the cellular level, TCTP can also act as an extracellular protein and as such has been involved in modulating whole-body defence processes, namely in the mammalian immune system. Extracellular TCTP, typically in its dimerised form, is able to induce the release of cytokines and other signalling molecules from various types of immune cells. There are also several examples, where TCTP was shown to be involved in antiviral/antibacterial defence in lower animals. In plants, the protein appears to have a protective effect against phytotoxic stresses, such as flooding, draught, too high or low temperature, salt stress or exposure to heavy metals. The finding for the latter stress condition is corroborated by earlier reports that TCTP levels are considerably up-regulated upon exposure of earthworms to high levels of heavy metals.Given the involvement of TCTP in many biological processes aimed at maintaining cellular or whole-body homeostasis, it is not surprising that dysregulation of TCTP levels may promote a range of disease processes, foremost cancer. Indeed a large body of evidence now supports a role of TCTP in at least the most predominant types of human cancers. Typically, this can be ascribed to both the anti-apoptotic activity of the protein and to its function in promoting cell growth and division. However, TCTP also appears to be involved in the later stages of cancer progression, such as invasion and metastasis. Hence, high TCTP levels in tumour tissues are often associated with a poor patient outcome. Due to its multiple roles in cancer progression, TCTP has been proposed as a potential target for the development of new anti-cancer strategies in recent pilot studies. Apart from its role in cancer, TCTP dysregulation has been reported to contribute to certain processes in the development of diabetes, as well as in diseases associated with the cardiovascular system.Since cellular TCTP levels are highly regulated, e.g. in response to cell stress or to growth signalling, and because deregulation of this protein contributes to many disease processes, a detailed understanding of regulatory processes that impinge on TCTP levels is required. The last section of this chapter summarises our current knowledge on the mechanisms that may be involved in the regulation of TCTP levels. Essentially, expression of the TPT1 gene is regulated at both the transcriptional and the translational level, the latter being particularly advantageous when a rapid adjustment of cellular TCTP levels is required, for example in cell stress responses. Other regulatory mechanisms, such as protein stability regulation, may also contribute to the regulation of overall TCTP levels.

Role of TCTP for Cellular Differentiation and Cancer Therapy

The translationally controlled tumor protein (TCTP) is a highly conserved protein that is regulated due to a high number of extracellular stimuli. TCTP has an important role for cell cycle and normal development. On the other side, tumor reversion and malignant transformation have been associated with TCTP. TCTP has been found among the 12 genes that are differentially expressed during mouse oocyte maturation, and an overexpression of this gene was reported in a wide variety of different cancer types. Its antiapoptotic effect is indicated by the interaction with several proapoptotic proteins of the Bcl-2 family and the p53 tumor suppressor protein. In this article, we draw attention to the role of TCTP in cancer, especially, focusing on cell differentiation and tumor reversion, a biological process by which highly tumorigenic cells lose their malignant phenotype. This protein has been shown to be the most strongly downregulated protein in revertant cells compared to the parental cancer cells. Decreased expression of TCTP results either in the reprogramming of cancer cells into reversion or apoptosis. As conventional chemotherapy is frequently associated with the development of drug resistance and high toxicity, the urge for the development of new or additional scientific approaches falls into place. Differentiation therapy aims at reinducing differentiation backward to the nonmalignant cellular state. Here, different approaches have been reported such as the induction of retinoid pathways and the use of histone deacetylase inhibitors. Also, PPARγ agonists and the activation of the vitamin D receptor have been reported as potential targets in differentiation therapy. As TCTP is known as the histamine-releasing factor, antihistaminic drugs have been shown to target this protein. Antihistaminic compounds, hydroxyzine and promethazine, inhibited cell growth of cancer cells and decreased TCTP expression of breast cancer and leukemia cells. Recently, we found that two antihistaminics, levomepromazine and buclizine, inhibited cancer cell growth by direct binding to TCTP and induction of cell differentiation. These data confirmed that TCTP is an exquisite target for anticancer differentiation therapy and antihistaminics have potential to be lead compounds for the direct interaction with TCTP as new inhibitors of human TCTP and tumor growth.

Expression of translationally controlled tumor protein (TCTP) gene of Dirofilaria immitis guided by transcriptomic screening

Dirofilaria immitis (heartworm) infections affect domestic dogs, cats, and various wild mammals with increasing incidence in temperate and tropical areas. More sensitive antibody detection methodologies are required to diagnose asymptomatic dirofilariasis with low worm burdens. Applying current transcriptomic technologies would be useful to discover potential diagnostic markers for D. immitis infection. A filarial homologue of the mammalian translationally controlled tumor protein (TCTP) was initially identified by screening the assembled transcriptome of D. immitis (DiTCTP). A BLAST analysis suggested that the DiTCTP gene shared the highest similarity with TCTP from Loa loa at protein level (97%). A histidine-tagged recombinant DiTCTP protein (rDiTCTP) of 40 kDa expressed in Escherichia coli BL21 (DE3) showed immunoreactivity with serum from a dog experimentally infected with heartworms. Localization studies illustrated the ubiquitous presence of rDiTCTP protein in the lateral hypodermal chords, dorsal hypodermal chord, muscle, intestine, and uterus in female adult worms. Further studies on D. immitis-derived TCTP are warranted to assess whether this filarial protein could be used for a diagnostic purpose.

TCTP as therapeutic target in cancers

The translationally controlled tumor protein (TCTP) is a highly conserved protein present in eukaryotic organisms. This protein, located both in the cytoplasmic and the nucleus, is expressed in various tissues and is regulated in response to a wide range of extracellular stimuli. TCTP interacts with itself and other protein including MCL1 and p53. TCTP has been shown to play an important role in physiological events, such as cell proliferation, cell death and immune responses but also in stress response and tumor reversion. Moreover, TCTP expression is associated with malignancy and chemoresistance. In this review, we will evaluate pathways regulated by TCTP and current inhibitory strategy to target TCTP in cancerous diseases.

Mmi1, the yeast homologue of mammalian TCTP, associates with stress granules in heat-shocked cells and modulates proteasome activity

As we have shown previously, yeast Mmi1 protein translocates from the cytoplasm to the outer surface of mitochondria when vegetatively growing yeast cells are exposed to oxidative stress. Here we analyzed the effect of heat stress on Mmi1 distribution. We performed domain analyses and found that binding of Mmi1 to mitochondria is mediated by its central alpha-helical domain (V-domain) under all conditions tested. In contrast, the isolated N-terminal flexible loop domain of the protein always displays nuclear localization. Using immunoelectron microscopy we confirmed re-location of Mmi1 to the nucleus and showed association of Mmi1 with intact and heat shock-altered mitochondria. We also show here that mmi1Δ mutant strains are resistant to robust heat shock with respect to clonogenicity of the cells. To elucidate this phenotype we found that the cytosolic Mmi1 holoprotein re-localized to the nucleus even in cells heat-shocked at 40°C. Upon robust heat shock at 46°C, Mmi1 partly co-localized with the proteasome marker Rpn1 in the nuclear region as well as with the cytoplasmic stress granules defined by Rpg1 (eIF3a). We co-localized Mmi1 also with Bre5, Ubp3 and Cdc48 which are involved in the protein de-ubiquitination machinery, protecting protein substrates from proteasomal degradation. A comparison of proteolytic activities of wild type and mmi1Δ cells revealed that Mmi1 appears to be an inhibitor of the proteasome. We conclude that one of the physiological functions of the multifunctional protein module, Mmi1, is likely in regulating degradation and/or protection of proteins thereby indirectly regulating the pathways leading to cell death in stressed cells.

The effect of translationally controlled tumour protein (TCTP) on programmed cell death in plants

BACKGROUND

Translationally controlled tumour protein (TCTP), a well known protein of the animal kingdom, was shown to be a Ca(2+)-binding protein with important functions in many different cellular processes (e.g. protection against stress and apoptosis, cell growth, cell cycle progression, and microtubule organization). However, only little is known about TCTP in plants. Transcript and protein levels of plant TCTPs were shown to be altered by various stress conditions (e.g. cold, salt, draught, aluminium, and pathogen infection), and Arabidopsis thaliana TCTP (AtTCTP) was described as an important regulator of growth. The aim of this study was to further characterize plant TCTP relating to one of its major functions in animals: the protection against cell death.

RESULTS

We used two different activators of programmed cell death (PCD) in plants: the mammalian pro-apoptotic protein BAX and tunicamycin, an inhibitor of glycosylation and trigger of unfolded protein response (UPR). Over-expression of AtTCTP significantly decreased cell death in tobacco leaf discs in both studies. A (45)Ca overlay assay showed AtTCTP to be a Ca(2+)-binding protein and localization experiments revealed cytosolic distribution of AtTCTP-GFP in Arabidopsis seedlings.

CONCLUSIONS

Our study showed cytoprotective effects of plant TCTP for the first time. Furthermore, we showed the ability of AtTCTP to bind to Ca(2+) and its cytosolic distribution within the cell. If these results are combined, two putative modes of action can be assumed: 1) AtTCTP acts as Ca(2+) sequester, preventing PCD by reducing cytosolic Ca(2+) levels as described for animals. 2) AtTCTP could directly or indirectly interact with other cytosolic or membrane-bound proteins of the cell death machinery, thereby inhibiting cell death progression. As no homologous proteins of the anti-apoptotic machinery of animals were found in plants, and functional homologues still remain to be elucidated, future work will provide more insight.

TCTP is an androgen-regulated gene implicated in prostate cancer

TCTP has been implicated in a plethora of important cellular processes related to cell growth, cell cycle progression, malignant transformation and inhibition of apoptosis. In addition to these intracellular functions, TCTP has extracellular functions and plays an important role in immune cells. TCTP expression was previously shown to be deregulated in prostate cancer, but its function in prostate cancer cells is largely unknown. Here we show that TCTP expression is regulated by androgens in LNCaP prostate cancer cells in vitro as well as human prostate cancer xenografts in vivo. Knockdown of TCTP reduced colony formation and increased apoptosis in LNCaP cells, implicating it as an important factor for prostate cancer cell growth. Global gene expression profiling in TCTP knockdown LNCaP cells showed that several interferon regulated genes are regulated by TCTP, suggesting that it may have a role in regulating immune function in prostate cancer. In addition, recombinant TCTP treatment increased colony formation in LNCaP cells suggesting that secreted TCTP may function as a proliferative factor in prostate cancer. These results suggest that TCTP may have a role in prostate cancer development.

(1)H, (15)N, and (13)C chemical shift assignments of the calflagin Tb24 flagellar calcium binding protein of Trypanosoma brucei

Flagellar calcium binding proteins are expressed in a variety of trypanosomes and are potential drug targets for Chagas disease and African sleeping sickness. We report complete NMR chemical shift assignments of the flagellar calcium binding protein calflagin Tb24 of Trypanosoma brucei. (BMRB no. 18011).

NMR structure of the calflagin Tb24 flagellar calcium binding protein of Trypanosoma brucei

Flagellar calcium binding proteins are expressed in a variety of trypanosomes and are potential drug targets for Chagas disease and African sleeping sickness. The flagellar calcium binding protein calflagin of Trypanosoma brucei (called Tb24) is a myristoylated and palmitoylated EF-hand protein that is targeted to the inner leaflet of the flagellar membrane. The Tb24 protein may also interact with proteins on the membrane surface that may be different from those bound to flagellar calcium binding proteins (FCaBPs) in T. cruzi. We report here the NMR structure of Tb24 that contains four EF-hand motifs bundled in a compact arrangement, similar to the overall fold of T. cruzi FCaBP (RMSD = 1.0 Å). A cluster of basic residues (K22, K25, K31, R36, and R38) located on a surface near the N-terminal myristoyl group may be important for membrane binding. Non-conserved residues on the surface of a hydrophobic groove formed by EF2 (P91, Q95, D103, and V108) and EF4 (C194, T198, K199, Q202, and V203) may serve as a target protein binding site and could have implications for membrane target recognition.

Biological effects of Mammalian translationally controlled tumor protein (TCTP) on cell death, proliferation, and tumorigenesis

Translationally controlled tumor protein (TCTP) is a highly conserved protein found in eukaryotes, across animal and plant kingdoms and even in yeast. Mammalian TCTP is ubiquitously expressed in various tissues and cell types. TCTP is a multifunctional protein which plays important roles in a number of cell physiological events, such as immune responses, cell proliferation, tumorigenicity, and cell death, including apoptosis. Recent identification of TCTP as an antiapoptotic protein has attracted interest of many researchers in the field. The mechanism of antiapoptotic activity, however, has not been solved completely, and TCTP might inhibit other types of cell death. Cell death (including apoptosis) is closely linked to proliferation and tumorigenesis. In this context, we review recent findings regarding the role of TCTP in cell death, proliferation, and tumorigenesis and discuss the mechanisms.

Physical and functional antagonism between tumor suppressor protein p53 and fortilin, an anti-apoptotic protein

Tumor suppressor protein p53, our most critical defense against tumorigenesis, can be made powerless by mechanisms such as mutations and inhibitors. Fortilin, a 172-amino acid polypeptide with potent anti-apoptotic activity, is up-regulated in many human malignancies. However, the exact mechanism by which fortilin exerts its anti-apoptotic activity remains unknown. Here we present significant insight. Fortilin binds specifically to the sequence-specific DNA binding domain of p53. The interaction of fortilin with p53 blocks p53-induced transcriptional activation of Bax. In addition, fortilin, but not a double point mutant of fortilin lacking p53 binding, inhibits p53-dependent apoptosis. Furthermore, cells with wild-type p53 and fortilin, but not cells with wild-type p53 and the double point mutant of fortilin lacking p53 binding, fail to induce Bax gene and apoptosis, leading to the formation of large tumor in athymic mice. Our results suggest that fortilin is a novel p53-interacting molecule and p53 inhibitor and that it is a logical molecular target in cancer therapy.

Mcl-1 functions as major epidermal survival protein required for proper keratinocyte differentiation

Rapid downregulation of the antiapoptotic Bcl-2 family protein myeloid cell leukemia 1 (Mcl-1) is required for UV-induced apoptosis, underlining an important role for Mcl-1 in epidermal pathology. To determine if Mcl-1 has a specific role in normal keratinocyte (KC) biology, Mcl-1 was downregulated in human KCs by RNAi and these KCs were induced to differentiate in organotypic raft cultures. Mcl-1 shRNA organotypic cultures showed increased levels of spontaneous premature apoptosis, implicating Mcl-1 as an essential KC survival protein. Mcl-1-downregulated cultures also had reduced granular and cornified layers, and produced lower levels of cross-linked protein and cornified envelopes. Cornification could only partially be rescued with the general caspase inhibitor z-VAD, suggesting that reduced cornification was not entirely because of premature apoptosis. Differentiation markers (K1, K10, filaggrin, loricrin, cleaved caspase-14) were normally expressed in control organotypic cultures, but were expressed at reduced levels in organotypic cultures with downregulated Mcl-1. The defect in differentiation marker expression was independent of apoptosis as it could not be rescued by z-VAD. Thus, Mcl-1 serves two important, independent functions in epidermal KCs: acting as a major survival protein by inhibiting premature apoptosis in the spinous and granular layers to promote conification, and promoting the robust induction of KC differentiation markers.

Proteomic analysis of parasitized Plutella xylostella larvae plasma

Insects use their innate immunity to defend themselves against foreign invaders, such as microorganisms, nematodes and parasites. Cotesia plutellae, an endoparasitoid wasp that parasitizes the diamondback moth Plutella xylostella, uses several strategies to attack the host immune system, such as injection of viruses, venom, and serosal membrane-derived cells denoted teratocytes. However, the proteome profiles related to these immune deficiency systems have yet to be clearly defined. In this study, we investigate differences in protein expression patterns in parasitized P. xylostella larvae, with a view to identifying parasitism-specific factors. Using 2D polyacrylamide gel electrophoresis, proteins in the host plasma were assessed every 48 h after parasitism by C. plutellae. A large number of protein spots (350 in total) were detected, and approximately 50 spots were differentially expressed in the parasitized P. xylostella larvae every 48 h. In total, 26 potential candidates, including P. xylostella Serpin 2 (pxSerpin 2), translationally controlled tumor protein, signal transduction histidine kinase, apolipophorin-III, and fatty-acid binding protein were identified through quadrupole time-of-flight tandem mass spectrometry and sequence homology analysis. These proteins were classified into the following functional groups: immunity, signaling, lipid metabolism, energy metabolism, amino acid/nucleotide metabolism, and others. The pxSerpin 2 gene was cloned, and its expression profile investigated during the course of parasitism. Real-time PCR analysis of pxSerpin 2 revealed a poor correlation between the mRNA level and protein abundance. Our results clearly suggest that parasitism-specific proteins participate in suppression of the host immune response.

Fortilin binds Ca2+ and blocks Ca2+-dependent apoptosis in vivo

Fortilin, a 172-amino-acid polypeptide present both in the cytosol and nucleus, possesses potent anti-apoptotic activity. Although fortilin is known to bind Ca2+, the biochemistry and biological significance of such an interaction remains unknown. In the present study we report that fortilin must bind Ca2+ in order to protect cells against Ca2+-dependent apoptosis. Using a standard Ca2+-overlay assay, we first validated that full-length fortilin binds Ca2+ and showed that the N-terminus (amino acids 1-72) is required for its Ca2+-binding. We then used flow dialysis and CD spectropolarimetry assays to demonstrate that fortilin binds Ca2+ with a dissociation constant (Kd) of approx. 10 mM and that the binding of fortilin to Ca2+ induces a significant change in the secondary structure of fortilin. In order to evaluate the impact of the binding of fortilin to Ca2+ in vivo, we measured intracellular Ca2+ levels upon thapsigargin challenge and found that the lack of fortilin in the cell results in the exaggerated elevation of intracellular Ca2+ in the cell. We then tested various point mutants of fortilin for their Ca2+ binding and identified fortilin(E58A/E60A) to be a double-point mutant of fortilin lacking the ability of Ca2+-binding. We then found that wild-type fortilin, but not fortilin(E58A/E60A), protected cells against thapsigargin-induced apoptosis, suggesting that the binding of fortilin to Ca2+ is required for fortilin to protect cells against Ca2+-dependent apoptosis. Together, these results suggest that fortilin is an intracellular Ca2+ scavenger, protecting cells against Ca2+-dependent apoptosis by binding and sequestering Ca2+ from the downstream Ca2+-dependent apoptotic pathways.

The salivary glands and saliva of Anopheles gambiae as an essential step in the Plasmodium life cycle: a global proteomic study

Proteins synthesized in the salivary glands of the Anopheles gambiae mosquito are thought to be important in the life cycle of the malaria parasite Plasmodium. To describe A. gambiae salivary gland and saliva contents, we combined several techniques: 1-DE, 2-DE and LC MS/MS. This study has identified five saliva proteins and 122 more proteins from the salivary glands, including the first proteomic description for 89 of these salivary gland proteins. Since the invasion and sporozoite maturation take place during the process of salivary glands ageing, the effect of salivary gland age on salivary component composition was examined. LC MS/MS profiling of young versus old salivary gland proteomes suggests that there is an over-representation of proteins involved in signaling and proteins related to the immune response in the proteins from older mosquitoes. The iTRAQ labeling was used for a comparative proteomic analysis of salivary gland samples from infected or Plasmodium berghei-free mosquitoes. The expression levels of five secreted proteins were altered when the parasite was present. These observations will serve as a basis for future work concerning the possible role of these proteins in the interaction between A. gambiae, Plasmodium and the mammalian host.

Use of comparative proteomics to identify potential resistance mechanisms in cancer treatment

Drug resistance is a major problem in successful cancer chemotherapy. Many molecular mechanisms that are responsible for drug resistance are known whereas others have yet to be discovered. Determining the exact mechanism activated in a particular case (clinical or laboratory) is a difficult task. Recently, proteomics has been applied to investigate drug resistance mechanisms in model cancer cell lines. As a result, novel mechanisms of resistance have been discovered and known mechanisms of resistance confirmed. In this paper, we wish to review recent developments and progresses in the application of proteomic tools to identify known and novel drug resistance mechanisms in drug-selected model cancer cell lines. Our combined analyses of multiple proteomic studies of various drug resistant cancer cell lines revealed that many mechanisms of resistance likely exist in any given drug-selected cancer cell line and that common mechanisms of resistance may be selected in a spectrum of cancer cell lines. These observations suggest that combination therapies targeting multiple mechanisms to sensitize drug resistant cancers may be necessary to eradicate cancers in the future.

Solution structure and mapping of a very weak calcium-binding site of human translationally controlled tumor protein by NMR

Human translationally controlled tumor protein (TCTP) is a growth-related, calcium-binding protein. We determined the solution structure and backbone dynamics of human TCTP, and identified the calcium-binding site of human TCTP using multi-dimensional NMR spectroscopy. The overall structure of human TCTP has a rather rigid well-folded core and a very flexible long loop connected by a short two-strand beta-sheet, which shows a conserved fold in the TCTP family. The C-terminal portions of loop L(alpha3beta8) and strand beta9 and the N-terminal region of strand beta8 may form a calcium-binding site in the human TCTP structure, which is largely conserved in the sequence alignment of TCTPs. The K(d) value for the calcium binding is 0.022-0.025 M indicating a very weak calcium-binding site.

Molecular cloning and characterization of the translationally controlled tumor protein gene in Bombyx mori

Translationally controlled tumor protein (Tctp/p23) is known to be synthesized preferentially in cells during the early growth phase of tumors, but is also expressed in normal cells. To elucidate its molecular basis of the expression and physiological significance, a cDNA encoding for the Bombyx mori Tctp (BmTctp) was deduced by editing the partial cDNA sequences registered in a Bombyx EST database. RT-PCR analyses indicated that the BmTCTP mRNA was transcribed in all larval organs examined and was present constantly during the cell cycle of BmN4 cells. A genomic clone of 4255 nucloetide residues produced by inverse PCR contained the 5'-flanking region, two introns and three exons of the BmTCTP gene. Sequence analysis of the 5'-flanking region indicated that a putative promoter region contains several canonical transcription elements such as GATA box, CCAAT motif, MEF2, E4BP4.01 and AP-1, but lacks a TATA box element. Luciferase reporter assay of the deletion constructs of the 5'-flanking region revealed that the -676 to +66 region enhanced the promoter activity the most markedly. In addition to this, there were at least two enhancer-like elements and several repressor elements.

Identification of the interaction between the human recombinant histamine releasing factor/translationally controlled tumor protein and elongation factor-1 delta (also known as eElongation factor-1B beta)

The human recombinant histamine releasing factor (HrHRF), also known as translationally controlled tumor protein (TCTP), p23 and fortilin, has been described to have both extra- and intracellular functions. To elucidate an extra- or intracellular role for HrHRF, we used the yeast two-hybrid system with HrHRF as the bait and a Jurkat T cell library. We isolated a partial cDNA clone of the human elongation factor-1 delta (EF-1delta) encoding for amino acids 12 to 281. This interaction was confirmed by co-immunoprecipitation experiments. Previously, both HrHRF and EF-1delta have been isolated and identified in association with malignancy in numerous studies. EF-1delta is part of the EF-1 complex responsible for kinetic proofreading in protein synthesis. Additionally, DNA microarray data classifies TCTP (HrHRF) as co-regulated with ribosomal proteins and recent structural analysis of TCTP (HrHRF) relates it to a guanine nucleotide-free chaperone. Our findings of an interaction between HrHRF and EF-1delta taken with some of the recently published information concerning the TCTP (HrHRF) mentioned above suggest a possible intracellular role for TCTP/HrHRF.

Molecular characterization of a calcium binding translationally controlled tumor protein homologue from the filarial parasites Brugia malayi and Wuchereria bancrofti

We have cloned homologues of the mammalian translationally controlled tumor protein (TCTP) from the human filarial parasites Wuchereria bancrofti and Brugia malayi. TCTP genes from B. malayi and W. bancrofti were expressed in a T7 promoter vector as histidine tagged fusion proteins. Both the recombinant B. malayi TCTP (rBm-TCTP) and recombinant W. bancrofti TCTP (rWb-TCTP) have a molecular mass of approximately 28 kDa with the histidine tag. Sequence analyses showed that there is a 98% similarity between the two filarial TCTPs at amino acid levels and are immunologically cross-reactive. Analysis of soluble proteins from various lifecycle stages of B. malayi suggested that the expression of Bm-TCTP might be differentially regulated and occurs in multimeric form. Recombinant TCTP were found to form multimers in solution under non-reducing conditions. The tendency for filarial TCTPs to become multimers was predicted by the presence of the Lupas coiled coil structure in their sequence. Despite the absence of a signal sequence, Bm-TCTP is present abundantly in the excretory/secretions (ES) of microfilariae. Characterization studies showed that both Bm- and Wb-TCTPs are calcium-binding proteins and have histamine-releasing function in vitro. When injected intraperitoneally both the filarial TCTPs induced inflammatory infiltration of eosinophils into the peritoneal cavity of mice suggesting that the filarial TCTPs may have a role in the allergic inflammatory responses associated with filarial infections.

Characterization of fortilin, a novel antiapoptotic protein

Apoptosis is meticulously controlled in living organisms. Its dysregulation has been shown to play a key role in a number of human diseases, including neoplastic, cardiovascular, and degenerative disorders. Bcl-2 family member proteins and inhibitors of apoptosis proteins are two major negative regulators of apoptosis. We report here the characterization of novel antiapoptotic protein, fortilin, which we identified through yeast two-hybrid library screening. Sequence analysis of fortilin revealed it to be a 172-amino acid polypeptide highly conserved from mammals to plants. Fortilin is structurally unrelated to either Bcl-2 family member proteins or inhibitors of apoptosis proteins. Northern blot analysis showed the fortilin message to be ubiquitous in normal tissue but especially abundant in the liver, kidney, and small intestine. Western blot analysis using anti-fortilin antibody showed more extensive expression in cancerous cell lines (H1299, MCF-7, and A549) than in cell lines derived from normal tissue (HEK293). Immunocytochemistry using HeLa cells transiently expressing FLAG-tagged fortilin and immunohistochemistry using human breast ductal carcinoma tissue and anti-fortilin antibody both showed that fortilin is predominantly localized in the nucleus. Functionally, the transient overexpression of fortilin in HeLa cells prevented them, in a dose-dependent fashion, from undergoing etoposide-induced apoptosis. Consistently, U2OS cells stably expressing fortilin protected the cells from cell death induced by etoposide over various concentrations and durations of exposure. In addition, fortilin overexpression inhibited caspase-3-like activity as assessed by the cleavage of fluorogenic substrate benzyloxycarbonyl-DEVD-7-amido-4-(trifluoromethyl)coumarin. Furthermore, the antisense depletion of fortilin from breast cancer cell line MCF-7 was associated with massive cell death. These data suggest that fortilin represents a novel antiapoptotic protein involved in cell survival and apoptosis regulation.

Identification of the self-interaction of rat TCTP/IgE-dependent histamine-releasing factor using yeast two-hybrid system

To further understand the biological function of translationally controlled tumor protein (TCTP), also known as IgE-dependent histamine-releasing factor (HRF), the yeast two-hybrid system was used to screen interacting molecules. We isolated cDNA clones coding for TCTP/HRF, suggesting that it may have a self-interacting property. Domain mapping of the interaction revealed that the C-terminal region of residue 126-172 is involved in self-interaction. The self-interacting property of TCTP/HRF was further supported by FPLC gel-filtration chromatography and coimmunoprecipitation analysis from transfected COS-7 cells. Our data suggests that TCTP/HRF may have a potential to self-interact through the C-terminal region, and the self-interaction property may be related to its biological function.

Identification of the calcium binding sites in translationally controlled tumor protein

Translationally controlled tumor protein (TCTP), also known as IgE-dependent histamine-releasing factor, is a growth-related tumor protein. Although the primary sequence of rat TCTP does not reveal any recognizable Ca2+ -binding motif, previous studies have demonstrated that rat TCTP consisting of 172 amino acids is a Ca2+ -binding protein. However, the region of TCTP required for Ca2+ interaction has not been mapped to the molecule. Here, we reported that the Ca2+ binding region of TCTP, which was mapped by using a combination of deletion constructs of rat TCTP and 45Ca2+ -overlay assay, was confined to amino acid residues 81-112. This binding domain did not show any peculiar loop of calcium-binding motif such as CaLB domain and EF hand motif and it seems to be constituted of random coil regions neighboring the a helix. Thus, our data confirm that TCTP is a novel family of Ca2+ -binding protein.

The Plasmodium falciparum translationally controlled tumor protein: subcellular localization and calcium binding

Artemisinin derivatives are endoperoxide antimalarials widely used to treat falciparum malaria in areas where drug resistance is common. In Plasmodium falciparum-infected erythrocytes, radiolabeled artemisinin derivatives have been shown to react with malarial proteins, one of which is the Translationally Controlled Tumor Protein (TCTP). The P. falciparum TCTP was found by immunofluorescence to be located in both the cytoplasm and food vacuoles. Immunoelectron microscopy shows that it is present in the parasite cytoplasm as well as in its food vacuolar and limiting membranes. Like other TCTPs, the P. falciparum protein binds to calcium. Further studies on the physiological role of TCTP may aid in understanding the mechanism of action of endoperoxide antimalarials.

The growth-related, translationally controlled protein P23 has properties of a tubulin binding protein and associates transiently with microtubules during the cell cycle

The translationally controlled protein P23 was discovered by the early induction of its rate of synthesis after mitogenic stimulation of mouse fibroblasts. P23 is expressed in almost all mammalian tissues and it is highly conserved between animals, plants and yeast. Based on its amino acid sequence, P23 cannot be attributed to any known protein family, and its cellular function remains to be elucidated. Here, we present evidence that P23 has properties of a tubulin binding protein that associates with microtubules in a cell cycle-dependent manner. (1) P23 is a cytoplasmic protein that occurs in complexes of 100–150 kDa, and part of P23 can be immunoprecipitated from HeLa cell extracts with anti-tubulin antibodies. (2) In immunolocalisation experiments we find P23 associated with microtubules during G1, S, G2 and early M phase of the cell cycle. At metaphase, P23 is also bound to the mitotic spindle, and it is detached from the spindle during metaphase-anaphase transition. (3) A GST-P23 fusion protein interacts with alpha- and beta-tubulin, and recombinant P23 binds to taxol-stabilised microtubules in vitro. The tubulin binding domain of P23 was identified by mutational analysis; it shows similarity to part of the tubulin binding domain of the microtubule-associated protein MAP-1B. (4) Overexpression of P23 results in cell growth retardation and in alterations of cell morphology. Moreover, elevation of P23 levels leads to microtubule rearrangements and to an increase in microtubule mass and stability.

Comparative phosphorylation of calmodulin from trypanosomatids and bovine brain by calmodulin-binding protein kinases

Calmodulin (CaM), a major intracellular Ca2+ receptor protein, has been identified and partially characterized in several trypanosomatids. The amino acid sequences of CaM from Trypanosoma cruzi and Trypanosoma brucei are known, while that from Leishmania mexicana is not. CaM from T. cruzi contains 18 amino acid substitutions, as compared with CaM from bovine brain. In addition, CaM from bovine brain contains two tyrosine residues (Tyr-99 and Tyr-138), while CaM from T. cruzi only contains Tyr-138. In the present work we show that a monoclonal antibody developed against the carboxyl-terminal region of bovine brain CaM fails to recognize CaM from both T. cruzi and L. mexicana. CaM from both parasites and from bovine brain were phosphorylated in vitro by a preparation of CaM-binding protein kinases enriched in the epidermal growth factor (EGF) receptor. Phosphoamino acids analysis demonstrated EGF-dependent phosphorylation of tyrosine residues in bovine brain CaM, while only trace amounts of tyrosine phosphorylation were detected in CaM from both trypanosomatids. These results demonstrate that the EGF receptor tyrosine kinase targets Tyr-99, but not Tyr-138, as the single major phosphorylatable residue of CaM. On the other hand, and in contrast to bovine brain CaM, there is a significant phosphorylation of serine residues in CaM from trypanosomatids which is activated by the EGF receptor via a protein-serine/threonine kinase cascade.

The Plasmodium falciparum translationally controlled tumor protein homolog and its reaction with the antimalarial drug artemisinin

Artemisinin and its derivatives are important new antimalarial drugs. When Plasmodium falciparum-infected erythrocytes are incubated with [10-3H]dihydroartemisinin, several malaria-specific proteins become labeled. One of these proteins is the P. falciparum translationally controlled tumor protein (TCTP) homolog. In vitro, dihydroartemisinin reacts covalently with recombinant TCTP in the presence of hemin. The association between drug and protein increases with increasing drug concentration, plateauing at approximately 1 drug/TCTP molecule. By Scatchard analysis, there appear to be 2 hemin binding sites on TCTP with dissociation constants of approximately 18 microM. When the single cysteine moiety is blocked by pretreatment with iodoacetamide, hemin binding is not affected, whereas drug binding is reduced by two-thirds. Thus, TCTP reacts with artemisinin in situ and in vitro in the presence of hemin and appears to bind to hemin. The function of the malarial TCTP and the role of this reaction in the mechanism of action of artemisinin await elucidation.

Differentially expressed, abundant trans-spliced cDNAs from larval Brugia malayi

Isolation and cloning of abundant reverse transcriptase-polymerase chain reaction (RT-PCR) products from the filarial nematode Brugia malayi using the conserved nematode spliced leader sequence and poly A as amplification targets has allowed us to identify abundant, stage specific transcripts from infective and post-infective larvae. The predicted protein products of the most prominent full-length transcripts from mosquito-derived L3 parasites are: (i) Bm-ALT-1, a homologue of a Dirofilaria immitis abundant larval protein: (ii) Bm-CPI-1, a cystatin-type cysteine protease inhibitor; (iii) Bm-ALT-3, a novel predicted 6 kDa glycine/tyrosine-rich protein; and (iv) Bm-TPH-1, a homologue of a mammalian translationally-controlled tumour protein. Some transcripts were not full-length but had mis-primed at A-rich stretches of coding sequence: the most abundant of these was Bm-col-3, a which encodes a collagen homologous to Bp-COL-1 of Brugia pahangi. Similar analysis of abundant spliced leader (SL)/oligo-dT products from fourth-stage larvae 9 days post-infection yielded two dominant transcripts: (i) Bm-cdd-1, which encodes a protein with homology to cytidine deaminase, differing at only one amino acid position from its homologue described in Brugia pahangi; and (ii) the same truncated form of Bm-col-3 found in L3 preparations. Expression of the major transcripts was assessed by PCR amplification of cDNA libraries derived from each stage of the life cycle. alt1, alt-3 and cpi-1 were all found to be specific to the L3 stage, while cdd-1 was found only in the L4 cDNA library. Expression of these larval-specific transcripts was not detected in either microfilarial or adult libraries.

Translationally controlled tumor protein: a protein identified in several nontumoral cells including erythrocytes

The translationally controlled tumor protein (TCTP) is a growth-related protein which is regulated at the translational level. It is present in mammals, higher plants and Saccharomyces cerevisiae. This study was undertaken to localize and further characterize the TCTP in human cell lysates using two-dimensional gel electrophoresis, monoclonal antibodies, and 45Ca-gel overlay. TCTP was found in several healthy and tumoral cells including erythrocytes, hepatocytes, macrophages, platelets, keratinocytes, erythroleukemia cells, gliomas, melanomas, hepatoblastomas, and lymphomas. It could not be detected in kidney and renal cell carcinoma (RCC). A monoclonal antibody raised against TCTP detected three isoforms likely due to post-translational modifications. A calcium binding property was found as well as heat stability and cytoplasmic localization. The high degree of homology from plants to man and its expression in many tissues suggests that TCTP most likely has a cell housekeeping function.

Calcium influx in Trypanosoma brucei can be induced by amphiphilic peptides and amines

The following study was undertaken to determine whether an inducible calcium influx pathway is present in intact bloodstream forms of Trypanosoma brucei. Fura-2 fluorescence was used to demonstrate that amphiphilic peptides and amines, including melittin, mastoparan and compound 48/80, each produced a dose dependent calcium influx across the plasma membrane. Calcium influx did not result from general disruption of membrane integrity, since a corresponding influx of ethidium bromide or other divalent cations was not observed. Instead, the calcium influx was selectively blocked by the calcium channel antagonists, La3+, Cd2+ or Ni2+, and was not affected by the Na+ channel antagonists, tetrodotoxin or amiloride. Activation of the trypanosome calcium influx pathway was dependent upon an intact membrane potential, and the rise in intracellular free calcium concentration ([Ca2+]i) was reversed upon membrane depolarization with gramicidin D. Changes in Ins(1,4,5)P3 did not accompany the calcium influx. Overall, these data provide the first evidence of an inducible calcium influx pathway in T. brucei, and describe methods to selectively manipulate this pathway.

Identification of a 44 kDa protein localized within the endoplasmic reticulum of Trypanosoma brucei brucei

Immunoaffinity chromatography and gel electrophoresis were used to isolate a 44 kDa protein that was bound to a 72 kDa chaperone in Trypanosoma brucei brucei. A polyclonal antiserum to the 44 kDa protein was raised in rats and employed in conjunction with chromatography using DEAE-cellulose, Sephacryl S-300, and hydroxyapatite to purify the protein from membranes of bloodstream forms of the trypanosomes. Immunoblot analysis using this antiserum revealed a protein doublet of 44/45 kDa in T. b. brucei and a single protein band of 53 kDa in almost equivalent amounts throughout the life-cycle stages of T. congolense. Indirect immunofluorescence using affinity-purified antibodies specific for the 44 kDa protein showed labelling of the perinuclear area and reticular system extending throughout the parasites, suggesting that this protein was located in the endoplasmic reticulum. Localization of the 44 kDa molecule in the endoplasmic reticulum was confirmed by immunoelectron microscopy. Protease protection experiments demonstrated that the epitopes bound by antibody were buried within the membrane or towards the lumenal face of the endoplasmic reticulum. Ruthenium Red overlay of nitrocellulose blots containing the 44/45 kDa doublet suggested that the molecules have the potential to bind calcium. The N-terminal amino acid sequence of the 44 kDa protein showed no sequence similarity to any proteins in the database.

Comparison of the 24 kDa flagellar calcium-binding protein cDNA of two strains of Trypanosoma cruzi

DNA sequences encoding the 24 kDa flagellar calcium binding protein (FCaBP) of two strains of Trypanosoma cruzi were found to differ at fourteen positions, six of which result in amino acid differences. Four of the amino acid differences are located within the calcium-binding domains of FCaBP; however, none is predicted to affect the calcium-binding ability of the protein. Chromosomes harboring the FCaBP gene clusters differ in size among T. cruzi strains.

The predominant calcimedins from Trypanosoma brucei comprise a family of flagellar EF-hand calcium-binding proteins

The cellular complement of calcimedins was identified in Trypanosoma brucei by Ca(2+)-dependent association with phenyl-Sepharose. Predominant calcimedins with molecular mass of 23-26 kDa and 44 kDa, along with minor calcimedins of 96, 120 and 230 kDa, were obtained. The trypanosome calcimedins were unrelated to vertebrate annexins, based upon antibody cross-reactivity and an inability to associate in a Ca(2+)-dependent way with phospholipid vesicles comprised of phosphatidylserine or phosphatidylethanolamine/phosphatidylcholine (1:1, w/w). Partial sequence analysis demonstrated that 44 kDa calcimedin (Tb-44) contained an EF-hand calcium-binding loop. Five CNBr/tryptic fragments exhibited a total of 93% similarity with Tb-17, a 23 kDa EF-hand protein in T. brucei. The trypanosome calcimedins appeared to comprise a family of proteins, based on sequence similarities and antibody cross-reactivity of affinity-purified anti-Tb44 with the 23-26 kDa cluster. No evidence was found for Tb-44 in the related species T. cruzi, Leishmania taraentolae or Crithidia fasciculata. Antibodies against Tb-44 were localized by immunofluorescence along the flagellum of T. brucei. Immunoblot analysis of flagella-enriched preparations demonstrated that Tb-44 and the 23-26 kDa cluster were present in this structure. We conclude that annexin family members are not among the predominant trypanosome proteins that associate with phenyl-Sepharose in a Ca(2+)-dependent way. Instead, the major trypanosome calcimedins comprise a family of flagellar EF-hand calcium-binding proteins.

Trypanosoma brucei: the tumor promoter thapsigargin stimulates calcium release from an intracellular compartment in slender bloodstream forms

Maintenance of calcium homeostasis is a critical activity of eukaryotic cells. Homeostatic pathways stabilize intracellular free calcium concentrations ([Ca2+]i) at the resting level and provide the source of mobilized calcium for cellular activation. We have measured calcium release from intracellular pools within bloodstream forms of Trypanosoma brucei to better understand homeostatic pathways which operate in these organisms. Fura-2 and 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein were used to quantitate [Ca2+]i and intracellular pH (pHi), respectively. We report that the tumor promoter, thapsigargin, elevated [Ca2+]i by 50-75 nM. Mn2+ quench experiments demonstrated that the source of calcium was intracellular. No change in pHi was associated with the release of calcium from this compartment. In contrast, nigericin released approximately three-fold more calcium than thapsigargin from a pH-sensitive, intracellular pool. The nigericin-sensitive pool was nonmitochondrial. The effects of thapsigargin and nigericin on [Ca2+]i were additive, regardless of the order in which the treatment was given. We conclude that at least two pools of exchangeable calcium occur in bloodstream forms of T. brucei. One pool is sensitive to thapsigargin and apparently resides within the endoplasmic reticulum, while the nigericin-sensitive pool is nonmitochondrial and is of unknown origin.