The efficient and rapid import of a peptide into primary B and T lymphocytes and a lymphoblastoid cell line

Selection of a novel cell-internalizing RNA aptamer specific for CD22 antigen in B cell acute lymphoblastic leukemia

Despite improvements in B cell acute lymphoblastic leukemia (B-ALL) treatment, a significant number of patients experience relapse of the disease, resulting in poor prognosis and high mortality. One of the drawbacks of current B-ALL treatments is the high toxicity associated with the non-specificity of chemotherapeutic drugs. Targeted therapy is an appealing strategy to treat B-ALL to mitigate these toxic off-target effects. One such target is the B cell surface protein CD22. The restricted expression of CD22 on the B-cell lineage and its ligand-induced internalizing properties make it an attractive target in cases of B cell malignancies. To target B-ALL and the CD22 protein, we performed cell internalization SELEX (Systematic Evolution of Ligands by EXponential enrichment) followed by molecular docking to identify internalizing aptamers specific for B-ALL cells that bind the CD22 cell-surface receptor. We identified two RNA aptamers, B-ALL1 and B-ALL2, that target human malignant B cells, with B-ALL1 the first documented RNA aptamer interacting with the CD22 antigen. These B-ALL-specific aptamers represent an important first step toward developing novel targeted therapies for B cell malignancy treatments.

Cell-Permeable Bak BH3 Peptide Induces Chemosensitization of Hematologic Malignant Cells

Hematologic malignancies such as leukemias and lymphomas are among the leading causes of pediatric cancer death worldwide, and although survival rates have improved with conventional treatments, the development of drug-resistant cancer cells may lead to patient relapse and limited possibilities of a cure. Drug-resistant cancer cells in these hematologic neoplasms are induced by overexpression of the antiapoptotic B-cell lymphoma 2 (Bcl-2) protein families, such as Bcl-_XL, Bcl-2, and Mcl-1. We have previously shown that peptides from the BH3 domain of the proapoptotic Bax protein that also belongs to the Bcl-2 family may antagonize the antiapoptotic activity of the Bcl-2 family proteins, restore apoptosis, and induce chemosensitization of tumor cells. Furthermore, cell-permeable Bax BH3 peptides also elicit antitumor activity and extend survival in a murine xenograft model of human B non-Hodgkin's lymphoma. However, the activity of the BH3 peptides of the proapoptotic Bak protein of the Bcl-2 family against these hematologic malignant cells requires further characterization. In this study, we report the ability of the cell-permeable Bak BH3 peptide to restore apoptosis and induce chemosensitization of acute lymphoblastic leukemia and non-Hodgkin's lymphoma cell lines, and this event is enhanced with the coadministration of cell-permeable Bax BH3 peptide and represents an attractive approach to improve the patient outcomes with relapsed or refractory hematological malignant cells.

Apoptosis and immaturity in acute myeloid leukemia

The primary cause of treatment failures in acute myeloid leukemia (AML) is the emergence of both resistant disease and early relapse. Among the most frequent agents of these phenomena are defects in the mitochondrial-mediated apoptotic pathway. This pathway is regulated by bcl-2 family of anti-apoptotic (bcl-2, bcl-xl, mcl-1) and pro-apoptotic proteins (bax, bad, bak). In particular, bcl-2 dimerizes with several members of bcl-2 family of proteins, altering the threshold of cell death. The flow cytometric quantitative measurement of bcl-2 and bax expression for the determination of bax/bcl-2 ratio provided crucial clinical information in AML: in our hands, lower bax/bcl-2 ratio conferred a very poor prognosis with decreased rates of complete remission (CR) and overall survival (OS). Moreover, striking correlations were found between lower bax/bcl-2 ratio and higher progenitor marker expression, such as CD34, CD117 and CD133 antigens, confirming the link between this apoptotic index and the maturation pathways. However, the capacity of bax/bcl-2 ratio to clearly identify patients with different prognosis with regard to CR and OS within the CD34+, CD117+ and CD133+ subgroups implies that other mechanisms, such as proliferation and/or cell cycle dysregulation may be involved to explain its clinical significance. Finally, small molecules that target both the receptor- and mitochondrial-mediated pathway of apoptosis are providing encouraging results in patients with relapsed and/or refractory disease (i.e. CDDOMe, bcl-2 antisense oligonucleotides, CEP-701, etc), confirming the key role of apoptotic mechanisms on the outcome of AML patients.

Protein delivery using engineered virus-like particles

Over the years, researchers have developed several methods to deliver macromolecules into the cytosol and nucleus of living cells. However, there are limitations to all of these methods. The problems include (i) inefficient uptake, (ii) endosomal entrapment, (iii) delivery that is restricted to certain cell types, and (iv) damage to cells in the delivery process. Retroviral vectors are often used for gene delivery; however, integration of the genome of retroviral vector into the host genome can have serious consequences. Here we describe a safe alternative in which virus-like particles (VLPs), derived from an avian retrovirus, are used to deliver protein to cells. We show that these VLPs are a highly adaptable platform that can be used to deliver proteins either as part of Gag fusion proteins (intracellular delivery) or on the surface of VLPs. We generated VLPs that contain Gag-Cre recombinase, Gag-Fcy::Fur, and Gag-human caspase-8 as a proof-of-concept and demonstrated that the encapsidated proteins are active in recipient cells. In addition, we show that murine IFN-γ and human TNF-related apoptosis-inducing ligand can be displayed on the surface of VLPs, and that these modified VLPs can cause the appropriate response in cells, as evidenced by phosphorylation of STAT1 and induction of cell death, respectively.

A gene delivery system based on the N-terminal domain of human topoisomerase I

The N-terminal 200 amino acid residues of topoisomerase I (TopoN) is highly positive in charge and has DNA binding activity, without DNA sequence and topological specificity. Here, a fusion protein (6 x His-PTD-TopoN) containing a hexahistidine (6 x His) tag, a membrane penetration domain and TopoN (amino acid 3-200) was designed and developed. The protein can bind to different sizes (3.0-8.0 kb) and forms (circular and linear) of DNA and translocates the bound DNA to the nucleus. The protein also showed low cytotoxicity to GF-1 grouper fish fin cells that were previously very sensitive and difficult to transfect in vitro. Maintaining the hexahistidine tag increased the protein's transfection efficiency in COS7 African green monkey kidney cells and simplified the purification process. The plasmid pEGFP-N1 was delivered into COS7 cells by the protein in ATP- and temperature-dependent manners. The results indicate that the binding ability of TopoN is very useful for DNA delivery and the carrier protein can be expressed in Escherichia coli without removal of the hexahistidine tag.

Internalization of nucleoside phosphates into live cells by complex formation with different CPPs and JBS-nucleoducin

Nucleoside phosphates can bind to many functional proteins like G-proteins or other GTP-binding proteins in signal transduction or translation processes. Till now internalization of nucleoside phosphates into live cells remains a challenge. We study the internalization of a fluorescent-labelled deoxyuridine triphosphate into HeLa cells and other adhesion and suspension cells. We use different cell-penetrating peptides and a cocktail suitable for formation of non-covalent complexes with the nucleotide. Internalization is observed by fluorescence microscopy, and the uptake efficiency is quantitatively estimated by fluorescence spectroscopy. The applied concentrations of CPPs and the cocktail were checked on cell viability (MTT test) and membrane integrity (bioluminescence test with peptidyl-luciferin), indicating that the CPPs and the complexes with the nucleotide are cytotoxic above certain concentrations. These concentrations depend on CPP and cell type and are the limiting factors for the cargo uptake.

Design strategies of fluorescent biosensors based on biological macromolecular receptors

Fluorescent biosensors to detect the bona fide events of biologically important molecules in living cells are increasingly demanded in the field of molecular cell biology. Recent advances in the development of fluorescent biosensors have made an outstanding contribution to elucidating not only the roles of individual biomolecules, but also the dynamic intracellular relationships between these molecules. However, rational design strategies of fluorescent biosensors are not as mature as they look. An insatiable request for the establishment of a more universal and versatile strategy continues to provide an attractive alternative, so-called modular strategy, which permits facile preparation of biosensors with tailored characteristics by a simple combination of a receptor and a signal transducer. This review describes an overview of the progress in design strategies of fluorescent biosensors, such as auto-fluorescent protein-based biosensors, protein-based biosensors covalently modified with synthetic fluorophores, and signaling aptamers, and highlights the insight into how a given receptor is converted to a fluorescent biosensor. Furthermore, we will demonstrate a significance of the modular strategy for the sensor design.

pH-sensitive carbonate apatite as an intracellular protein transporter

The transfer of specific proteins into living cells to enable the regulation of cell function or the tracking of the intracellular distribution of proteins is a desirable objective for offering a potential alternative to gene therapy. Here, protein/carbonate apatite complexes were successfully fabricated for intracellular delivery of functional proteins since the carbonate apatite being highly water solubility under an acidic condition could easily be dissolved in endosomes following endocytosis, thus releasing the electrostatically associated proteins in cytoplasm. In this study, we characterized protein/carbonate apatite complexes as an intracellular protein delivery system and we checked intracellular delivery of proteins by carbonate apatite nanoparticles in vitro. Fluorescently-labeled bovine serum albumin as a model protein was effectively delivered into nearly 100% of HeLa cells by the simple addition of protein/carbonate apatite complexes to the cells. Confocal microscopic imaging suggested the endosomal release of protein delivered with carbonate apatite. And intracellularly delivered ss-galactosidase did not lose its enzymatic activity. These results suggested that intracellular delivery system of protein using pH-sensitive carbonate apatite carrier with a very simple procedure will be a highly effective method to the biological and clinical researches.

Efficient intracellular delivery of functional proteins using cationic polymer core/shell nanoparticles

Cationic core/shell nanoparticles self-assembled from biodegradable, cationic and amphiphilic copolymer poly{N-methyldietheneamine sebacate)-co-[(cholesteryl oxocarbonylamido ethyl) methyl bis(ethylene) ammonium bromide] sebacate}, P(MDS-co-CES), were fabricated and employed to deliver lectin A-chain, an anticancer glycoprotein. Lectin A-chain was efficiently bound onto the surfaces of the nanoparticles at high mass ratios of nanoparticles to lectin A-chain. The nanoparticle/lectin A-chain complexes had an average size of approximately 150 nm with zeta potential of about +30 mV at the mass ratio of 50 or above while the BioPorter/lectin A-chain complexes had a larger particle size and relatively lower zeta potential (150 nm vs. 455 nm; +30 mV vs. +20 mV). Therefore, the cellular uptake of nanoparticle/lectin A-chain complexes was much greater than that of BioPorter/lectin A-chain complexes. The results obtained from cytotoxicity tests show that lectin A-chain delivered by the nanoparticles was significantly more toxic against MDA-MB-231, HeLa, HepG2 and 4T1 cell lines when compared to BioPorter, and IC50 of lectin A-chain delivered by the nanoparticles was 0.2, 0.5, 10 and 50 mg/l, respectively, while that of lectin A-chain delivered by BioPorter was higher than 100 mg/l in all cell lines tested. These nano-sized particles may provide an efficient approach for intracellular delivery of biologically active proteins.

Determination of sphingosine kinase activity for cellular signaling studies

Regulation of sphingosine and sphingosine-1-phosphate concentrations is of growing interest due to their importance in cellular signal transduction. Furthermore, new pharmaceutical agents moderating the intracellular and extracellular levels of sphingosine metabolites are showing promise in preclinical and clinical trials. In the present work, a quantitative assay relying on capillary electrophoresis with laser-induced fluorescence detection was developed to measure the interconversion of sphingosine and sphingosine-1-phosphate. The assay was demonstrated to be capable of determining the in vitro activity of both kinase and phosphatase using purified enzymes. The KM of sphingosine kinase for its fluorescently labeled substrate was 38 +/- 18 microM with a Vmax of 0.4 +/- 0.2 microM/min and a kcat of 3900 s-1. Pharmacologic inhibition of sphingosine kinase in a concentration-dependent manner was also demonstrated. Moreover, the fluorescent substrate was shown to be readily taken up by mammalian cells making it possible to study the endogenous activity of sphingosine kinase activity in living cells. The method was readily adaptable to the use of either bulk cell lysates or very small numbers of intact cells. This new methodology provides enhancements over standard methods in sensitivity, quantification, and manpower for both in vitro and cell-based assays.

Myristoyl-based transport of peptides into living cells

Translocation of membrane-impermeant molecules to the interior of living cells is a necessity for many biochemical investigations. Myristoylation was studied as a means to introduce peptides into living cells. Uptake of a myristoylated, fluorescent peptide was efficient in the B lymphocyte cell line BA/F3. In contrast, this cell line was resistant to uptake of a cell-penetrating peptide derived from the TAT protein. In BA/F3 cells, membrane association was shown to be rapid, reaching a maximum within 30 min. Cellular uptake of the peptide lagged the membrane association but occurred within a similar time frame. Experiments performed at 37 versus 4 degrees C demonstrated profound temperature dependence in the cellular uptake of myristoylated cargo. Myristoylated peptides with either positive or negative charge were shown to load efficiently. In contrast to TAT-conjugated cargo, pyrenebutyrate did not enhance cellular uptake of the myristoylated peptide. The myristoylated peptide did not adversely affect cell viability at concentrations up to 100 muM. This assessment of myristoyl-based transport provides fundamental data needed in understanding the intracellular delivery of myristoylated peptide cargoes for cell-based biochemical studies.

Medium-sized peptides as built in carriers for biologically active compounds

A growing number of oligopeptides of natural and/or synthetic origin have been described and considered as targeting structures for delivery bioactive compounds into various cell types. This review will outline the discovery of peptide sequences and the corresponding mid-sized oligopeptides with membrane translocating properties and also summarize de novo designed structures possessing similar features. Conjugates and chimera constructs derived from these sequences with covalently attached bioactive peptide, epitope, oligonucleotide, PNA, drug, reporter molecule will be reviewed. A brief note will refer to the present understanding on the uptake mechanism at the end of each section.

Delivery of bioactive molecules into the cell: the Trojan horse approach

In recent years, vast amounts of data on the mechanisms of neural de- and regeneration have accumulated. However, only in disproportionally few cases has this led to efficient therapies for human patients. Part of the problem is to deliver cell death-averting genes or gene products across the blood-brain barrier (BBB) and cellular membranes. The discovery of Antennapedia (Antp)-mediated transduction of heterologous proteins into cells in 1992 and other "Trojan horse peptides" raised hopes that often-frustrating attempts to deliver proteins would now be history. The demonstration that proteins fused to the Tat protein transduction domain (PTD) are capable of crossing the BBB may revolutionize molecular research and neurobiological therapy. However, it was only recently that PTD-mediated delivery of proteins with therapeutic potential has been achieved in models of neural degeneration in nerve trauma and ischemia. Several groups have published the first positive results using protein transduction domains for the delivery of therapeutic proteins in relevant animal models of human neurological disorders. Here, we give an extensive review of peptide-mediated protein transduction from its early beginnings to new advances, discuss their application, with particular focus on a critical evaluation of the limitations of the method, as well as alternative approaches. Besides applications in neurobiology, a large number of reports using PTD in other systems are included as well. Because each protein requires an individual purification scheme that yields sufficient quantities of soluble, transducible material, the neurobiologist will benefit from the experiences of other researchers in the growing field of protein transduction.

RhoA and zeta PKC control distinct modalities of LFA-1 activation by chemokines: critical role of LFA-1 affinity triggering in lymphocyte in vivo homing

Chemokines regulate rapid leukocyte adhesion by triggering a complex modality of integrin activation. We show that the small GTPase RhoA and the atypical zeta PKC differently control lymphocyte LFA-1 high-affinity state and rapid lateral mobility induced by chemokines. Activation of LFA-1 high-affinity state and lateral mobility is controlled by RhoA through the activity of distinct effector regions, demonstrating that RhoA is a central point of diversification of signaling pathways leading to both modalities of LFA-1 triggering. In contrast, zeta PKC controls LFA-1 lateral mobility but not affinity triggering. Blockade of the 23-40 RhoA effector region prevents induction of LFA-1 high-affinity state as well as lymphocyte arrest in Peyer's patch high endothelial venules. Thus, RhoA controls the induction of LFA-1 high-affinity state by chemokines independently of zeta PKC, and this is critical to support chemokine-regulated homing of circulating lymphocytes.

Signaling and protein associations of a cell permeable CD40 complex in B cells

Signaling through the CD40 receptor activates diverse molecular pathways in a variety of immune cell types. To study CD40 signaling complexes in B cells, we produced soluble CD40 cytoplasmic domain multimers that translocate across cell membranes and engage intracellular CD40 signaling pathways. As visualized by fluorescence microscopy, rapid transduction of recombinant Antennapedia-isoleucine zipper (Izip)-CD40 cytoplasmic domain fusion protein (Antp-CD40) occurred in both the DND39 B cell line and human tonsillar B cells. Upon cellular entry, Antp-CD40 activated NF-kappaB-dependent transcription, induced proteolytic processing of p100 to the p52/NF-kappaB2 subunit, and increased expression of CD80 and CD54 on the surface of B cells. Antp-CD40 transduction of B cells did not, however, activate detectable levels of p38 mitogen-activated protein kinase or c-Jun N-terminal kinase and did not up-regulate CD95 expression. Analysis of Antp-CD40 complexes recovered from transduced B cells revealed that Antp-CD40 associated with endogenous TRAF3 and Ku proteins. Multimerization of Antp-CD40, or extensive clustering of transmembrane CD40, diminished the disruptive effect of the T254A mutation in the TRAF2/3 binding site of the CD40 cytoplasmic domain. Taken together, these results indicate that Antp-CD40 mimics some of the natural CD40 signaling pathways in B cells by assembling partially functional signaling intermediates that do not require plasma membrane localization. We present a novel approach for delivering pre-activated, soluble receptor cytoplasmic domains into cells and recovering intact signaling complexes for molecular analysis.

Suppression of gene expression by a cell-permeable Tet repressor

Engineered transcription factors designed to selectively activate or repress endogenous genes have great potential in medical and biotechnological applications. Ultimately, their success will depend on the development of efficient delivery systems. We show here that a chimeric tetracycline- controlled transcription factor, encompassing the Tet repressor (TetR) from the tetracycline-resistance operon (tet from Escherichia coli transposon Tn10) and a cell membrane transducing peptide, is able to regulate transcription from a tetracycline responsive promoter (pCMV2xtetO2). When added directly to cultured cells, TetR fused to the full-length Antennapedia homeodomain (AntpHD) from Drosophila (TetRAntp), was able to selectively repress transcription in cells transiently transfected with a tetracycline-regulated reporter transcription unit. Moreover, TetRAntp could repress expression of a tetracycline responsive reporter transcription unit stably integrated into the genome of HeLa cells, demonstrating the possibility of manipulating endogenous gene expression by cell-permeable transcription factors.

Taking the cell by stealth or storm? Protein transduction domains (PTDs) as versatile vectors for delivery

A cell delivery system is increasing in use in many areas of cell and molecular biology and bio-medicine. This system is based on a number of naturally occurring protein motifs and/or sequences which show the remarkable ability to rapidly cross the mammalian cell membrane without compromising its structure or function. These so-called Protein Transduction Domains (PTDs) offer unprecedented advantages for intracellular delivery. These advantages include, but are not limited to, their applicability to all cell types (no cell type has yet been described which is not transduced by these PTDs), and the range of cargoes that can be transduced (including peptides, small proteins, full-length enzymes, DNA oligomers, peptide-nucleic acid oligomers, liposomes, and magnetic nanoparticles). Furthermore, the PTDs have been demonstrated to be suitable for in vivo delivery including delivery across the blood brain barrier, and have been shown to cross the plasma membrane rapidly and enter the cytoplasm and nuclear regions of the cell. In this review, the general properties of the most commonly used PTDs are described. The strategies currently being undertaken also highlight that improvements in membrane transduction are possible despite our lack of understanding of the exact biochemical and/or physical mechanisms of transduction. Recent examples of the range of potential applications are also discussed.

Peptide delivery to the brain via adsorptive-mediated endocytosis: advances with SynB vectors

Biological membranes normally restrict the passage of hydrophilic molecules. This impairs the use of a wide variety of drugs for biomedical applications. To overcome this problem, researchers have developed strategies that involve conjugating the molecule of interest to one of a number of peptide entities that are efficiently transported across the cell membranes. In the past decade, a number of different peptide families with the ability to cross the cell membranes have been identified. Certain of these families enter the cells by a receptor-independent mechanism, are short (10-27 amino acid residues), and can deliver successfully various cargoes across the cell membrane into the cytoplasm or nucleus. Surprisingly, some of these vectors, the SynB vectors, have also shown the ability to deliver hydrophilic molecules across the blood-brain barrier, one of the major obstacles to the development of drugs to combat diseases affecting the CNS.

Molecular characterization of CD40 signaling intermediates

Signal transduction through the CD40 receptor is initiated by binding of its trimeric ligand and propagated by interactions of tumor necrosis factor receptor-associated factor (TRAF) proteins with the multimerized CD40 cytoplasmic domain. Using defined multimeric constructs of the CD40 cytoplasmic domain expressed as either soluble or myristoylated proteins, we have addressed the extent of receptor multimerization needed to initiate signal transduction and identified components of CD40 signaling complexes. Signal transduction in human embryonic kidney 293 cells, measured by nuclear factor kappaB activation, was observed in cells expressing soluble trimeric CD40 cytoplasmic domain and to a lesser extent in cells expressing dimeric CD40 cytoplasmic domain. Nuclear factor kappaB activation was strongest in cells expressing myristoylated trimeric CD40 cytoplasmic domain. Signal transduction through trimeric CD40 cytoplasmic domains with various point mutations in the TRAF binding sites was similar to signal transduction through analogous full-length receptors. Transiently expressed soluble trimeric CD40 cytoplasmic domain was isolated as complexes that contained TRAF2, TRAF3, TRAF5, TRAF6, and the inhibitor of apoptosis protein (c-IAP1). Association of c-IAP1 with the CD40 cytoplasmic domain complex was indirect and dependent on the presence of an intact TRAF1/2/3 binding site. These results suggest that extracellular ligation of CD40 can be bypassed and that soluble trimerized CD40 complexes can be isolated and used to identify components that link CD40 with signaling pathways.

Cellular delivery of impermeable effector molecules in the form of conjugates with peptides capable of mediating membrane translocation

Most molecules that are not actively imported by living cells are impermeable to cell membranes, including practically all macromolecules and even many small molecules whose physicochemical properties prevent passive membrane diffusion. The use of peptide vectors capable of transporting such molecules into cells in the form of covalent conjugates has become an increasingly attractive solution to this problem. Not only has this technology permitted the study of modulating intracellular target proteins, but it has also gained importance as an alternative to conventional cellular transfection with oligonucleotides. Peptide vectors derived from viral, bacterial, insect, and mammalian proteins endowed with membrane translocation properties have now been proposed as delivery vectors. These are discussed comprehensively and critically in terms of relative utility, applications to compound classes and specific molecules, and relevant conjugation chemistry. Although in most cases the mechanisms of membrane translocation are still unclear, physicochemical studies have been carried out with a number of peptide delivery vectors. Unifying and distinguishing mechanistic features of the various vectors are discussed. Until a few years ago speculations that it might be possible to deliver peptides, proteins, oligonucleotides, and impermeable small molecules with the aid of cellular delivery peptides not only to target cells in vitro, but in vivo, was received with scepticism. However, the first studies showing pharmacological applications of conjugates between macromolecules and peptide delivery vectors are now being reported, and therapies based on such conjugates are beginning to appear feasible.

Intracellular delivery of proteins with a new lipid-mediated delivery system

There are many very effective methods to introduce transcriptionally active DNA into viable cells but approaches to deliver functional proteins are limited. We have developed a lipid-mediated delivery system that can deliver functional proteins or other bioactive molecules into living cells. This delivery system is composed of a new trifluoroacetylated lipopolyamine (TFA-DODAPL) and dioleoyl phosphatidylethanolamine (DOPE). This cationic formulation successfully delivered antibodies, dextran sulfates, phycobiliproteins, albumin, and enzymes (beta-galactosidase and proteases) into the cytoplasm of numerous adherent and suspension cells. Two systems were used to demonstrate that the proteins were delivered in a functionally active form. First, intracellular beta-galactosidase activity was clearly demonstrated within X-gal-stained cells after TFA-DODAPL:DOPE-mediated delivery of the enzyme. Second, the delivery system mediated delivery of several caspases (caspase 3, caspase 8, and granzyme B) into cultured cell lines and primary cells triggering apoptosis. Mechanistic studies showed that up to 100% of the protein mixed with the lipid formulation was captured into a lipid-protein complex, and up to 50% of the input protein associated with cells. This lipid-mediated transport system makes protein delivery into cultured cells as convenient, effective, and reliable as DNA transfection.

Exogenous antigens and the stimulation of MHC class I restricted cell-mediated cytotoxicity: possible strategies for fish vaccines

An MHC class I restricted cytotoxic T lymphocyte (CTL) activity assay has recently been established for rainbow trout. MHC class I restricted cytotoxicity probably plays a critical role in immunity to most viral diseases in mammals and may play a similar role in fish. Therefore, it is very important to investigate what types of vaccines can stimulate this immune response. Although logical candidates for vaccine components that can stimulate an MHC class I restricted response are live attenuated viruses and DNA vaccines, these materials are generally not allowed in fish for commercial vaccine use due to potential safety issues. In mammals, however, a number of interesting vaccination strategies based on exogenous antigens that stimulate MHC class I restricted cytotoxicity have been described. Several of these strategies are discussed in this review in the context of fish vaccination.

Characterization of hybrid CTL epitope delivery systems consisting of the Antennapedia homeodomain peptide vector formulated in liposomes

Peptide carriers, such the homeodomain of Antennapedia molecule (AntpHD), which spontaneously cross cellular membranes, have been exploited to deliver antigenic peptide Cw3 to the major histocompatibility complex (MHC) class-I presentation pathway and to prime cytotoxic T cells (CTL). However, the in vivo use of AntpHD recombinant peptide has been limited because CTLs can only be primed in the presence of sodium dodecyl sulfate (SDS) as adjuvant. In this report, we have exploited liposomes to protect the AntpHD-Cw3 from serum degradation and to facilitate the delivery of the recombinant peptide into the MHC class-I pathway of antigen-presenting cells. We have demonstrated that AntpHD recombinant peptide spontaneously associates with liposomes and this association is stable in vitro. However, exchange studies assessing the transfer of the peptide to model membranes or cells in vitro indicates that approximately 50% of the liposome-associated peptide is readily exchangeable. This is consistent with trypsin-protection assays, which have shown that approximately 40% of the liposome-associated peptide is protected from hydrolysis. Importantly, macrophages and dendritic cells are able to internalize AntpHD recombinant peptide associated with liposomes resulting in efficient delivery of the CTL peptide into the cytosol. These studies have demonstrated that dendritic cells treated with AntpHD-Cw3 in liposomes sensitize CTL clones to lyse syngeneic target cells expressing Cw3 epitope. This strategy, which combines liposomes and a peptide vector, provides a new approach for introducing molecules into the MHC class-I antigen presentation pathway of dendritic cells.

The BH3 domain of BAD fused to the Antennapedia peptide induces apoptosis via its alpha helical structure and independent of Bcl-2

Since the over-expression of Bcl-2 is a common cause of multi-drug resistance, cytotoxic peptides that overcome the effects of Bcl-2 may be clinically useful. We harnessed the death-promoting alpha helical properties of the BH3 domain of BAD by fusing it to the Antennapedia (ANT) domain, which allows for cell entry (ANTBH3BAD). Treatment of 32D cells with the ANTBH3BAD peptide results in a 99% inhibition of colony formation. No significant toxicity is observed after treatment with ANT or BH3BAD alone. A mutant fusion peptide unable to bind Bcl-2 induces cell death as effectively as the wild-type ANTBH3BAD. Furthermore, 32D cells over-expressing Bcl-2 show no resistance to the ANTBH3BAD peptide. Therefore, the toxicity of the peptide was independent of the Bcl-2 pathway. We demonstrate that the toxicity of the peptide is due to its alpha helicity that disrupts mitochondrial function. Since this peptide overcomes major forms of drug resistance, it may be therapeutically useful if appropriately targeted to malignant cells.

Physico-chemical requirements for cellular uptake of pAntp peptide. Role of lipid-binding affinity

The pAntp peptide, corresponding to the third helix of the Antennapedia homeodomain, is internalized by a receptor-independent process into eucaryotic cells. The precise mechanism of entry remains unclear but the interaction between the phospholipids of plasma membrane and pAntp is probably involved in the translocation process. In order to define the role of peptide-lipid interaction in this mechanism and the physico-chemical properties that are necessary for an efficient cellular uptake, we have carried out an Ala-Scan mapping. The peptides were labeled with a fluorescent group (7-nitrobenz-2-oxo-1,3-diazol-4-yl-; NBD) and their cell association was measured by flow cytometry. Furthermore, we determined the fraction of internalized peptide by using a dithionite treatment. Comparison between cell association and cell uptake suggests that the affinity of pAntp for the plasma membrane is required for the import process. To further investigate which are the physico-chemical requirements for phospholipid-binding of pAntp, we have determined the surface partition coefficient of peptides by titrating them with phospholipid vesicles having different compositions. In addition, we estimated by circular dichroism the conformation adopted by these peptides in a membrane-mimetic environment. We show that the phospholipid binding of pAntp depends on its helical amphipathicity, especially when the negative surface charge density of phospholipid vesicles is low. The cell uptake of pAntp, related to lipid-binding affinity, requires a minimal hydrophobicity and net charge. As pAntp does not seem to translocate through an artificial phospholipid bilayer, this might indicate that it could interact with other cell surface components or enters into cells by a nonelucidated biological mechanism.

Translocation of the pAntp peptide and its amphipathic analogue AP-2AL

The pAntp peptide, corresponding to the third helix of the homeodomain of the Antennapedia protein, enters by a receptor-independent process into eukaryotic cells. The interaction between the pAntp peptide and the phospholipid matrix of the plasma membrane seems to be the first step involved in the translocation mechanism. However, the mechanism by which the peptide translocates through the cell membrane is still not well established. We have investigated the translocation ability of pAntp through a protein-free phospholipid membrane in comparison with a more amphipathic analogue. We show by fluorescence spectroscopy, circular dichroism, NMR spectroscopy, and molecular modeling that pAntp is not sufficiently helically amphipathic to cross a phospholipid membrane of a model system. Due to its primary sequence related to its DNA binding ability in the Antennapedia homeodomain-DNA complex, the pAntp peptide does not belong to the amphipathic alpha-helical peptide family whose members are able to translocate by pore formation.

A retro-inverso peptide homologous to helix 1 of c-Myc is a potent and specific inhibitor of proliferation in different cellular systems

In 1998 we reported that an L-peptide derived from H1 of c-Myc (Int-H1-S6A,F8A), linked to an internalization sequence from the third a-helix of Antennapedia, was endowed with an antiproliferative and proapoptotic activity toward a human mammary cancer cell line: The activity apparently depends upon the presence of the Myc motif. In the present work we have added new dimensions to our original findings. It is known that short retro-inverso (RI-) peptides can assume a 3D conformation very close to their corresponding L-forms and can be recognized by the same monoclonal antibody. We synthesized a RI-peptide form of our original L-peptide: It was much more resistant to serum peptidases than the original molecule (a half life of days rather than hours); in addition, the RI-form of the original Antennapedia internalization sequence was perfectly capable of carrying a D-peptide into human cells. We have studied three different potentially active peptides. L-peptides: Int-H1wt, Int-H1-S6A,F8A. D-peptides: RI-Int -H1-S6A,F8A. We have also studied three presumed control peptides: Int and RI-Int (no H1 motif), H1-S6A,F8A (no internalization sequence). Both 'active' and 'control' peptides have essentially confirmed our expectations, however, in cells treated with the higher concentration (10 mM) of the control peptide RI-Int, non-Myc related side effects could be detected. In order to investigate whether the antiproliferative activities displayed by some of our molecules were indeed related to an interference with the role of c-Myc (and molecules of the family), we chose an iso-amphipathic modified peptide of the H1 motif, with a proximity coefficient >50% and where the major change was at position 7 (F-->A). From a family of 73 H1 motifs belonging to (H1-Loop-H2) hu man sequences, the smallest evolutionary distance from our reference peptide was observed for the H1 of N-Myc, L-Myc, c-Myc, H1-S6A,F8A of c-Myc, and Max, in that order. Our reference peptide was therefore appropriate as a check of whether we were indeed observing activities related to Myc functions. Both Int-H1isoamph and the corresponding RI-Int-H1isoamph peptide were synthesized and studied. In terms of biological targets, we added to the human mammary cancer line of our previous work (MCF-7 cells) a colon cancer line (HCT-116 cells) and also a system of normal cells: human peripheral blood lymphocytes (PBLs) stimulated with phytohemoagglutinin (PHA). Peptides carrying an iso-amphipathic-modified H1 sequence were always very clearly (3-10 times) less active than the corresponding peptides carrying a conserved "H1 of Myc" motif. This finding was noted in five independent situations (all the cellular models considered at the present time): MCF-7 cells treated with L-peptides; MCF-7 cells treated with RI-peptides; HCT-116 cells treated with L-peptides; PBLs treated with L-peptides; PBLs treated with RI-peptides. Modulation of transcription levels of ornithine decarboxylase (ODC), p53, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), in PBLs treated with our different molecules, was well compatible with an interference by our active peptides at the level of Myc transcriptional activity. We had already reported a similar observation in MCF-7 cells. On a molar basis, RI-peptides were about 5-10 times more potent and 30-35 times more stable in complete culture medium, than their corresponding L-forms. RI-Int can probably internalize longer peptido-mimetic molecules (for instance molecules mimetic of (H1-Loop-H2), or even more. These possibilities open the way to rodent studies and to more potent/selective Myc inhibitors-two steps closer to a potential drug.

Cellular uptake and in situ binding of a peptide agonist for calmodulin

We have used the method of inverted hydropathy to develop peptides that interact with EF hands of calmodulin (CaM). Previously we have shown these peptides specifically interact with their desired target in a productive manner, in that they activated CaM in the absence of Ca(2+). Therefore, we sought to determine whether these peptides would enter cells, remain intact, and interact with CaM in the interior of the cell. Using several techniques we have demonstrated cellular uptake, stability, and an intracellular interaction with CaM with fluorescein-labeled and radiolabeled peptides in Jurkat T cells. The results suggest that these peptides may be useful in the study and the manipulation of Ca(2+)-mediated pathways in cells.

Protein transduction: unrestricted delivery into all cells?

Several proteins can traverse biological membranes through protein transduction. Small sections of these proteins (10-16 residues long) are responsible for this. Linking these domains covalently to compounds, peptides, antisense peptide nucleic acids or 40-nm iron beads, or as in-frame fusions with full-length proteins, lets them enter any cell type in a receptor- and transporter-independent fashion. Moreover, several of these fusions, introduced into mice, were delivered to all tissues, even crossing the blood-brain barrier. These domains thus might let us address new questions and even help in the treatment of human disease.

T cell receptor-induced calcineurin activation regulates T helper type 2 cell development by modifying the interleukin 4 receptor signaling complex

The activation of downstream signaling pathways of both T cell receptor (TCR) and interleukin 4 receptor (IL-4R) is essential for T helper type 2 (Th2) cell development, which is central to understanding immune responses against helminthic parasites and in allergic and autoimmune diseases. However, little is known about how these two distinct signaling pathways cooperate with each other to induce Th2 cells. Here, we show that successful Th2 cell development depends on the effectiveness of TCR-induced activation of calcineurin. An inhibitor of calcineurin activation, FK506, inhibited the in vitro anti-TCR-induced Th2 cell generation in a dose-dependent manner. Furthermore, the development of Th2 cells was significantly impaired in naive T cells from dominant-negative calcineurin Aalpha transgenic mice, whereas that of Th1 cells was less affected. Efficient calcineurin activation in naive T cells upregulated Janus kinase (Jak)3 transcription and the amount of protein. The generation of Th2 cells induced in vitro by anti-TCR stimulation was inhibited significantly by the presence of Jak3 antisense oligonucleotides, suggesting that the Jak3 upregulation is an important event for the Th2 cell development. Interestingly, signal transducer and activator of transcription (STAT)5 became physically and functionally associated with the IL-4R in the anti-TCR-activated developing Th2 cells that received efficient calcineurin activation, and also in established cloned Th2 cells. In either cell population, the inhibition of STAT5 activation resulted in a diminished IL-4-induced proliferation. Moreover, our results suggest that IL-4-induced STAT5 activation is required for the expansion process of developing Th2 cells. Thus, Th2 cell development is controlled by TCR-mediated activation of the Ca(2+)/calcineurin pathway, at least in part, by modifying the functional structure of the IL-4R signaling complex.

Divergent requirements for the MAPK(ERK) signal transduction pathway during initial virus infection of quiescent primary B cells and disruption of Epstein-Barr virus latency by phorbol esters

Quiescent primary B lymphocytes and Epstein-Barr virus (EBV)-immortalized lymphoblastoid cell lines express components of the extracellular response kinase arm of the mitogen-activated protein kinase (MAPK(ERK)) signal transduction pathway and transmit signals through the pathway when exposed to appropriate stimuli. Although the MAPK(ERK) pathway is activated following infection with EBV, MAPK/ERK kinase (MEK1) activity is not required to drive the proliferation of infected cells. However, MEK1 contributes to EBV latency control.