Transduction of a functional domain of the AT1 receptor in neurons by HIV-Tat PTD

Tapasin modification on the intracellular epitope HBcAg18-27 enhances HBV-specific CTL immune response and inhibits hepatitis B virus replication in vivo

HBV-specific cytotoxic T-lymphocyte (CTL) activity has a very important role in hepatitis B virus clearance. Present studies suggest that Tapasin, a endoplasmic reticulum (ER) chaperone, stabilizes the peptide-receptive MHC I conformation, allowing peptide exchange and increasing more peptides to be translocated into the ER. We have previously testified that cytoplasmic transduction peptide (CTP)-HBcAg(18-27)-Tapasin fusion protein could enter cytoplasm of dendritic cells, and enhance T cells' response to generate specific CTLs efficiently in vitro. In the present study, we evaluated specific immune responses of CTP-HBcAg(18-27)-Tapasin fusion protein in HLA-A2 transgenic mice (H-2K(b)) and anti-viral ability in HBV transgenic mice, and explored the mechanisms probably involved in. The studies showed that CTP-HBcAg(18-27)-Tapasin not only increased production of cytokine IFN-γ and interleukin-2 (IL-2), compared with CTP-HBcAg(18-27), HBcAg(18-27)-Tapasin, and PBS, but also significantly induced the higher percentages of IFN-γ+CD8(+) T cells and specific CTL responses in HLA-A2 transgenic mice. Moreover, enhancement of specific CTL activity induced by the fusion protein reduced HBV DNA and hepatitis B surface antigen (HBsAg) levels and decreased the expression of HBsAg and hepatitis B core antigen (HBcAg) in liver tissue of HBV transgenic mice. In addition, CTP-HBcAg(18-27)-Tapasin could upregulate the expression of JAK2, Tyk2, STAT1, and STAT4 in T lymphocytes in HLA-A2 transgenic mice splenocytes. However, there was no significant difference on the expressions of JAK1, JAK3, and STAT6 between each group. In conclusion, CTP-HBcAg(18-27)-Tapasin fusion protein could enhance not only the percentages of CTLs but also induce robust specific CTL activity and inhibits hepatitis B virus replication in vivo, which was associated with activation of the JAK/STAT signaling pathway.

Slit diaphragm protein Neph1 and its signaling: a novel therapeutic target for protection of podocytes against glomerular injury

Podocytes are specialized epithelial cells that are critical components of the glomerular filtration barrier, and their dysfunction leads to proteinuria and renal failure. Therefore, preserving podocyte function is therapeutically significant. In this study, we identified Neph1 signaling as a therapeutic target that upon inhibition prevented podocyte damage from a glomerular injury-inducing agent puromycin aminonucleoside (PAN). To specifically inhibit Neph1 signaling, we used a protein transduction approach, where the cytoplasmic domain of Neph1 (Neph1CD) tagged with a protein transduction domain trans-activator of transcription was transduced in cultured podocytes prior to treatment with PAN. The PAN-induced Neph1 phosphorylation was significantly reduced in Neph1CD-transduced cells; in addition, these cells were resistant to PAN-induced cytoskeletal damage. The biochemical analysis using subfractionation studies showed that unlike control cells Neph1 was retained in the lipid raft fractions in the transduced cells following treatment with PAN, indicating that transduction of Neph1CD in podocytes prevented PAN-induced mislocalization of Neph1. In accordance, the immunofluorescence analysis further suggested that Neph1CD-transduced cells had increased ability to retain endogenous Neph1 at the membrane in response to PAN-induced injury. Similar results were obtained when angiotensin was used as an injury-inducing agent. Consistent with these observations, maintaining high levels of Neph1 at the membrane using a podocyte cell line overexpressing chimeric Neph1 increased the ability of podocytes to resist PAN-induced injury and PAN-induced albumin leakage. Using a zebrafish in vivo PAN and adriamycin injury models, we further demonstrated the ability of transduced Neph1CD to preserve glomerular function. Collectively, these results support the conclusion that inhibiting Neph1 signaling is therapeutically significant in preventing podocyte damage from glomerular injury.

Limiting angiotensin II signaling with a cell-penetrating peptide mimicking the second intracellular loop of the angiotensin II type-I receptor

A cell-penetrating peptide consisting of the second intracellular loop (IC2) of the angiotensin II (AngII) type-I receptor (AT1) linked to the HIV-transactivating regulatory protein (TAT) domain was used to identify the role of this motif In intracellular signal transduction. HEK-293 cells stably transfected with AT1R cDNA and primary cultures of human pulmonary artery smooth muscle cells expressing endogenous AT1 receptor were exposed to the cell-penetrating peptide construct, and the effect on angiotensin II signaling was determined. The AT1 IC2 peptide effectively inhibited AngII-stimulated phosphatidylinositol turnover and calcium influx. It also limited the activation of Akt/PKB as determined by an inhibition of phosphorylation of Akt at Ser473, and completely abolished the AngII-dependent activation of the transcriptional factor NFkappaB. In contrast, the AT1 IC2 peptide had no effect on AngII/AT1 receptor activation of ERK. These results illustrate the potential of using cell-penetrating peptides to both delineate receptor-mediated signal transduction and to selectively regulate G protein-coupled receptor signaling.

Development of a soluble PTD-HPV18E7 fusion protein and its functional characterization in eukaryotic cells

Though accumulated evidence has demonstrated the transformation capacity of human papillomavirus (HPV) type 18 protein E7, the underlying mechanism is still arguable. Developing a protein transduction domain (PTD)-linked E7 molecule is a suitable strategy for assessing the biological functions of the protein. In the present study, HPV18 E7 protein fused to an N-terminal PTD was expressed in the form of glutathione S-transferase fusion protein in Escherichia coli with pGEX-4T- 3 vector. After glutathione-Sepharose 4B bead affinity purification, immunoblot identification and thrombin cleavage, the PTD-18E7 protein showed structural and functional activity in that it potently transduced the cells and localized into their nuclei. The PTD-18E7 protein transduced the NIH3T3 cells in 30 min and remained stable for at least 24 h. In addition, the PTD-18E7 protein interacted with retinoblastoma protein (pRB) and caused pRB degradation in the transduced NIH3T3 cells. In contrast to the pRB level, p27 protein level was elevated in the transduced NIH3T3 cells. The PTD-18E7 protein gives us a new tool to study the biological functions of the HPV E7 protein.

TAT-mediated intracellular protein delivery to primary brain cells is dependent on glycosaminoglycan expression

Although some studies have shown that the cell penetrating peptide (CPP) TAT can enter a variety of cell lines with high efficiency, others have observed little or no transduction in vivo or in vitro under conditions mimicking the in vivo environment. The mechanisms underlying TAT-mediated transduction have been investigated in cell lines, but not in primary brain cells. In this study we demonstrate that transduction of a green fluorescent protein (GFP)-TAT fusion protein is dependent on glycosaminoglycan (GAG) expression in both the PC12 cell line and primary astrocytes. GFP-TAT transduced PC12 cells and did so with even higher efficiency following NGF differentiation. In cultures of primary brain cells, TAT significantly enhanced GFP delivery into astrocytes grown under different conditions: (1) monocultures grown in serum-containing medium; (2) monocultures grown in serum-free medium; (3) cocultures with neurons in serum-free medium. The efficiency of GFP-TAT transduction was significantly higher in the monocultures than in the cocultures. The GFP-TAT construct did not significantly enter neurons. Experimental modulation of GAG content correlated with alterations in TAT transduction in PC12 cells and astrocyte monocultures grown in the presence of serum. In addition, this correlation was predictive of TAT-mediated transduction in astrocyte monocultures grown in serum free medium and in coculture. We conclude that culture conditions affect cellular GAG expression, which in turn dictates TAT-mediated transduction efficiency, extending previous results from cell lines to primary cells. These results highlight the cell-type and phenotype-dependence of TAT-mediated transduction, and underscore the necessity of controlling the phenotype of the target cell in future protein engineering efforts aimed at creating more efficacious CPPs.

Human PEP-1-ribosomal protein S3 protects against UV-induced skin cell death

The consequences of ultraviolet (UV) exposure are implicated in skin aging and cell death. The ribosomal protein S3 (rpS3) is one of the major proteins by which cells counteract the deleterious effects of UV and it plays a role in the repair of damaged DNA. In the present study, we investigated the protective effects of PEP-1-rpS3 fusion protein after UV-induced cell injury. A human rpS3 gene was fused with PEP-1 peptide in a bacterial expression vector to produce a genetic in-frame PEP-1-rpS3 fusion protein. The expressed and purified fusion proteins were efficiently transduced into skin cells in a time- and dose-dependent manner. Once inside the cells, transduced PEP-1-rpS3 fusion protein was stable for 48h. We showed that transduced PEP-1-rpS3 fusion protein increased cell viability and dramatically reduced DNA lesions in the UV exposed skin cells. Immunohistochemical analysis revealed that PEP-1-rpS3 fusion protein efficiently penetrated the epidermis as well as the dermis of the subcutaneous layer when sprayed on animal skin. These results suggest that PEP-1-rpS3 fusion protein can be used in protein therapy for various disorders related to UV, including skin aging and cancer.

The taming of the cell penetrating domain of the HIV Tat: myths and realities

Protein transduction with cell penetrating peptides over the past several years has been shown to be an effective way of delivering proteins in vitro and now several reports have also shown valuable in vivo applications in correcting disease states. An impressive bioinspired phenomenon of crossing biological barriers came from HIV transactivator Tat protein. Specifically, the protein transduction domain of HIV Tat has been shown to be a potent pleiotropic peptide in protein delivery. Various approaches such as molecular modeling, arginine guanidinium head group structural strategy, multimerization of PTD sequence and phage display system have been applied for taming of the PTD. This has resulted in identification of PTD variants which are efficient in cell membrane penetration and cytoplasmic delivery. In spite of these state of the art technologies, the dilemma of low protein transduction efficiency and target specific delivery of PTD fusion proteins remains unsolved. Moreover, some misconceptions about PTD of Tat in the literature require considerations. We have assembled critical information on secretory, plasma membrane penetration and transcellular properties of Tat and PTD using molecular analysis and available experimental evidences.

The kinetics and tissue distribution of protein transduction in mice

Protein transduction domains (PTDs) offer an exciting therapeutic opportunity for the treatment of many diseases. An 11-amino acid fragment of human immunodeficiency type 1 (HIV-1) TAT-protein can transduce large, biologically active proteins into mammalian cells; recent evidence has shown an in vivo PTD for the 116 kDa beta-galactosidase protein. However, there is little information on the in vivo distribution of the TAT fusion protein to define the viability of PTDs for human studies. In this study we examined the tissue kinetics and tissue distribution of the PTD-transduced TAT fusion protein in mice. Low (100 microg) or high (500 microg) doses of TAT-beta-galactosidase fusion protein were administrated to mice through four routes (portal vein, i.v., i.p., and oral). Tissues were harvested 15 min, 1h, 6h, 10h, and 24h after treatment. Distribution of beta-galactosidase in various tissues was analysed by in situ staining, enzymatic activity assay, and Western blot analysis. Beta-galactosidase enzyme activity was observed in all tissues (liver, kidney, spleen, lung, bowel, and brain). Beta-galactosidase activity peaked at 15 min in most tissues after portal vein, i.v., and i.p. administration and at 1h after oral dosing in all tissues. Beta-galactosidase activity in the liver at 15 min after portal vein injection (67 milliunits [mU]/mg) was higher than after i.v. (9.8 mU/mg), i.p. (4.4 mU/mg), and oral (0.3 mU/mg) dosing. In situ staining and Western blot results correlated closely with beta-galactosidase enzyme activity assay. The median initial half-life for activity was 2.2h, ranging from 1.2h to 3.4h (coefficient of variation=28.9%). The bioavailability of beta-galactosidase activity after an orally administered PTD was 24%. This study details the kinetics and tissue distribution of delivering of a model TAT fusion protein into the mouse via PTD. These data allow rational selection of delivery route and schedules for therapeutic PTD and will aid the use of TAT fusion protein transduction in the development of protein therapies.

Peptide-enhanced cellular internalization of proteins in neuroscience

Over the last 15 years, many publications described the use of peptide sequences that have been dubbed cell penetrating peptides (CPP), Trojan Horse peptides, protein transduction domains, or membrane-translocating sequences. These mostly positively charged domains bring attached cargo across biological membranes. One of the reasons for the interest in CPP is their potential as delivery tools to enhance the pharmacodynamics of drugs otherwise poorly bioavailable. In particular, the neuroscientist aiming to deliver a protein or other compound into the brain for analytical or therapeutic reasons is faced with the challenge that few drugs cross the blood-brain barrier. CPP are valuable tools to overcome the plasma membrane or the blood-brain barrier in basic research, and in relevant models of neural disease, and will hopefully help to increase the precious few treatments or even cures for people with diseases of the brain and nervous system. Here, we review applications in neuroscience and recent insights into the mechanism of CPP-mediated trafficking.

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.

Effects on synaptic activity in cultured hippocampal neurons by influenza A viral proteins

Certain viruses can infect neurons and cause persistent infections with restricted expression of viral proteins. To study the consequences of such viral proteins on synaptic functions, the effects of two influenza A virus proteins, the nonstructural protein 1 (NS1) and the nucleoprotein (NP), were analyzed in cultures of rat hippocampal neurons. Transduction of the NS1 and NP proteins into the neurons was performed by applying the 11-amino acid peptide transduction domain (PTD) of human immunodeficiency virus (HIV) TAT coupled to the viral proteins. Neurons exposed to the NS1 and NP fusion proteins (NS1-PTD and NP-PTD, respectively) for 4 h were immunopositive for these proteins as diffuse cytoplasmic and nuclear distribution. After exposure for 48 h to NP-PTD, a punctate pattern of the immunolabel appeared in dendritic spinelike processes. Electrophysiologically, a reduction in both the frequency of spontaneous excitatory synaptic activity and in the amplitude of the miniature excitatory postsynaptic currents were recorded after exposing the hippocampal neurons to NP-PTD between 17 and 22 days in culture. These changes may reflect disturbances in postsynaptic functions. No such alterations in synaptic activities were recorded after exposure to NS1-PTD or to green fluorescent protein-PTD, which was used as a control. Based on these findings the authors hypothesize that the viral NP, by its localization to dendritic spinelike structures, interferes with the expression or anchoring of postsynaptic glutamate receptors and thereby disturbs synaptic functions. Thus a persistent viral infection in the brain may be associated with functional disturbances at the synaptic level.

Tat-calpastatin fusion proteins transduce primary rat cortical neurons but do not inhibit cellular calpain activity

Excessive activation of calpains (calcium-activated neutral proteases) is observed following spinal cord contusion injury, traumatic brain injury, stroke, and in neurodegenerative disorders including Alzheimer's disease. Calpain inhibition represents an attractive therapeutic target, but current calpain inhibitors possess relatively weak potency, poor specificity, and in many cases, limited cellular and blood-brain barrier permeability. We developed novel calpain inhibitors consisting of the endogenous inhibitor, calpastatin or its inhibitory domain I, fused to the protein transduction domain of the HIV trans-activator (Tat) protein (Tat(47-57)). The Tat-calpastatin fusion proteins were potent calpain inhibitors in a cell-free activity assay, but did not inhibit cellular calpain activity in primary rat cortical neurons when applied exogenously at concentrations up to 5 microM. The fusion proteins were able to transduce neurons, but were localized within endosome-like structures. A similar endosomal uptake was observed for Tat-GFP. Together, the results suggest that endosomal uptake of the Tat-calpastatin prevents its interaction with calpain in other cellular compartments. Endosomal uptake of proteins fused to the Tat protein transduction domain severely limits the applications of this methodology.

Functional genomics as an emerging strategy for the investigation of central mechanisms in experimental hypertension

Centrally mediated increases in sympathetic nerve activity and attenuated arterial baroreflexes contribute to the pathogenesis of hypertension. Despite the characterization of cellular and physiological mechanisms that regulate blood pressure and alterations that contribute to hypertension, the genetic and molecular basis of this pathophysiology remains poorly understood. Strategies to identify genes that contribute to central pathophysiologic mechanisms in hypertension include integrative biochemistry and physiology as well as functional genomics. This article summarizes recent progress in applying functional genomics to elucidate the genetic basis of altered central blood pressure regulatory mechanisms in hypertension. We describe approaches others and we have undertaken to investigate gene expression profiles in hypertensive models in order to identify genes that contribute to the pathogenesis of hypertension. Finally, we provide the readers a roadmap for negotiating the route from experimental findings of gene expression profiling to translating their therapeutic potential. The combination of gene expression profiling and the phenotypic characterization of in vitro and in vivo loss or gain of function experiments for candidate genes have the potential to identify genes involved in the pathogenesis of hypertension and may present novel targets for therapy.