Transduction of TAT fusion proteins into osteoclasts and osteoblasts

It has been difficult to transduce primary cultures of bone cells with proteins of interest. Here, we report the development and validation of a new technology for transduction of osteoblasts and osteoclasts with peptides and moderately sized proteins. Fusion proteins between TAT, an 11 amino acid Arg-rich sequence derived from the HIV protein, and either hemagglutinin or calcineurin Aalpha were synthesized and purified. Exposure of osteoblasts and osteoclasts in primary culture to either TAT-HA or TAT-calcineurin Aalpha resulted in a rapid (within 10 min) intracellular movement of the fusion protein evident on co-immunostaining. Almost 99% of cells were transduced and the fusion protein was retained in approximately 50% of the cells for up to 5 days. TAT did not abolish the functionality of calcineurin Aalpha; the fusion protein stimulated osteoblast differentiation and inhibited osteoclastic resorption. We expect that our studies will provide a firm basis for the future development of TAT fusion proteins for critical molecules involved in bone cell differentiation and function.     

Production of cell lines secreting TAT fusion proteins.

Transduction of proteins and other macromolecules constitutes a potent technology to analyze cell functions and to achieve therapeutic interventions. In general, fusion proteins with protein transduction domains, such as TAT, are produced in a bacterial expression system. Here we describe the generation of a mammalian expression vector coding for TAT-EGFP fusion protein. Transfection of CHO-K1 cells by this vector and subsequent selection by Zeocin resulted in cell lines that express and secrete EGFP, a variant of the green fluorescent protein GFP. The ultimate cell line was produced by first cloning the stable integrants and subsequent selection of EGFP-expressing cells by flow cytometric sorting. In the resulting cell line approximately 98% of cells express EGFP. Using the same methodology, we generated cell lines that express DsRed fluorescent protein. The advantages of using such a mammalian expression system include the ease of generating TAT fusion proteins and the potential for sustained production of such proteins in vitro and, potentially, in vivo.     

Comparison of protein transduction domains in mediating cell delivery of a secreted CRE protein

Protein transduction domains (PTDs) are versatile peptide sequences that facilitate cell delivery of several cargo molecules including proteins. PTDs usually consist of short stretches of basic amino acids that can cross the plasma membrane and gain entry into cells. Traditionally, to assess PTD mediated protein delivery, PTD-fusion proteins have been used as purified proteins. To overcome the requirement for a protein purification step, we used a secretory signal peptide to allow PTD-CRE fusion proteins to be exported from transfected mammalian cells. PTD induced protein transduction into cells was assessed by a CRE-mediated recombination event that resulted in beta-galactosidase expression. Several PTDs were tested including the prototypic TAT, different TAT variants, Antp, MTS and polyarginine. A negative correlation was observed between the cationic charge on the PTD and the extent of secretion. Poor secretion was found when the PTD charge was greater than +5. One TAT-CRE protein variant had a 14-fold enhancement above CRE alone when added to cells in the presence of chloroquine. This PTD domain also enhanced gene expression after plasmid delivery. These data illustrate that some secreted PTD proteins may be useful reagents to improve protein delivery in mammalian systems and a novel approach to enhancing the response to DNA transfections.     

Induction of antigen-specific CTL by recombinant HIV trans-activating fusion protein-pulsed human monocyte-derived dendritic cells

Several systems have been tested for introduction of Ags into human dendritic cells (DC). Most of them to date, however, are complex and possess limited efficiency. Recent advances in HIV trans-activating (TAT) fusion protein technology permit extremely high transduction efficiencies for a majority of mammalian cell types. Here we report our attempts to develop a simple, but highly efficient, protocol for loading of antigenic protein into DC using TAT fusion technology. A TAT-minigene fusion protein was generated, encoding both the HLA-A2-restricted influenza matrix protein-derived epitope (GILVFTFTL, Flu-M1) and a melanoma Ag gp100-derived modified epitope (YLEPGPVTV, G9(280)-9V). In addition, both a TAT-Her2/neu extracellular domain (ECD) fusion protein and a TAT-green fluorescence protein fusion protein were generated. Over 95% of DC stained positively for TAT-green fluorescence protein within 20 min of coculture. DC treated with TAT-minigene were efficiently recognized by both Flu-M1 and G9(280)-9V-specific T cells in cytotoxicity assays and IFN-gamma ELISPOT assays. In contrast, DC pulsed with minigene fusion protein lacking TAT were either poorly recognized or not recognized by the T cells. DC pulsed with TAT-minigene also efficiently induced Flu-M1-specific T cells from naive lymphocytes. Similarly, DC treated with TAT-Her2/neu ECD stimulated patient-derived lymphocytes that specifically recognized Her2/neu(+) ovarian and breast cancer cell lines. The CTL induced by TAT-Her2/neu ECD-pulsed DC specifically recognized the Her2/neu ECD-derived immunogenic peptide E75 (KIFGSLAFL). Our data suggest that TAT fusion proteins efficiently transduce DC and induce Ag-specific T cells. This could prove to be a useful method for treatment of infectious diseases and cancer.     

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. Biotechnol. Bioeng. 2009; 104: 10–19 © 2009 Wiley Periodicals, Inc.     

p38L12 TAT融合肽对山梨糖醇引起的 ECV304细胞ATF2磷酸化的抑制作用

构建p38 Loop-12(L12)的TAT融合表达载体,纯化原核表达的p38L12融合蛋白并鉴定其在真核细胞内的功能.利用PCR方法分别扩增出p38L12及其“T-X-Y”双磷酸化位点的AF突变体p38L12（AF）片段,克隆入His标记的TAT-EGFP融合蛋白原核表达载体pHTE（pET14b-His-TAT-EGFP）,经酶切、测序鉴定正确后,将重组质粒转化原核表达菌,诱导表达纯化融合蛋白;将融合蛋白加入ECV304细胞后于荧光显微镜下观察并行Western印迹分析,检测融合蛋白的细胞内转导活性;通过检测内源性ATF2磷酸化水平,鉴定高渗刺激下p38L12对内源性p38活性的影响.成功构建了p38L12和p38L12(AF)片段与TAT的融合表达载体,并获得相应的融合蛋白.在ECV304细胞中可见导入的HTE-p38L12和THE-p38L12(AF)融合蛋白具有较高的细胞内转导活性和转导效率,并可竞争性抑制高渗刺激对内源性p38的活化.基于HIV-1 TAT细胞转导系统证实p38L12可竞争性抑制高渗刺激诱导的内源性p38对ATF2的活化,从而发挥对p38激活特异性抑制的功能.     

Transduction of human catalase mediated by an HIV-1 TAT protein basic domain and arginine-rich peptides into mammalian cells.

Antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) have been considered to have a beneficial effect against various diseases mediated by reactive oxygen species (ROS). Although a variety of modified recombinant antioxidant enzymes have been generated to protect against the oxidative stresses, the lack of their transduction ability into cells resulted in limited ability to detoxify intracellular ROS. To render the catalase enzyme capable of detoxifying intracellular ROS when added extracellularly, cell-permeable recombinant catalase proteins were generated. A human liver catalase gene was cloned and fused with a gene fragment encoding the HIV-1 Tat protein transduction domain (RKKRRQRRR) and arginine-rich peptides (RRRRRRRRR) in a bacterial expression vector to produce genetic in-frame Tat-CAT and 9Arg-CAT fusion proteins, respectively. The expressed and purified fusion proteins can be transduced into mammalian cells (HeLa and PC12 cells) in a time- and dose-dependent manner when added exogenously in culture medium, and transduced fusion proteins were enzymatically active and stable for 60 h. When exposed to H(2)O(2), the viability of HeLa cells transduced with Tat-CAT or 9Arg-CAT fusion proteins was significantly increased. In combination with transduced SOD, transduced catalase also resulted in a cooperative increase in cell viability when the cells were treated with paraquat, an intracellular antioxide anion generator. We then evaluated the ability of the catalase fusion proteins to transduce into animal skin. This analysis showed that Tat-CAT and 9Arg-CAT fusion proteins efficiently penetrated the epidermis as well as the dermis of the subcutaneous layer when sprayed on animal skin, as judged by immunohistochemistry and specific enzyme activities. These results suggest that Tat-CAT and 9Arg-CAT fusion proteins can be used in protein therapy for various disorders related to this antioxidant enzyme.     

HIV-1 TAT-mediated protein transduction and subcellular localization using novel expression vectors

Several novel prokaryotic and eukaryotic expression vectors were constructed for protein transduction and subcellular localization. These vectors employed an N-terminal stretch of 11 basic amino acid residues (47-57) from the human immunodeficiency virus type 1 (HIV-1) TAT protein transduction domain (PTD) for protein translocation and cellular localization. The vectors also contained a six-histidine (His(6)) tag at the N- or C-terminus for convenient purification and detection, and a multiple cloning site for easy insertion of foreign genes. Some heterologous genes including HSV-TK, Bcl-rambo, Smac/DIABLO and GFP were fused in-frame to TAT PTD and successfully overexpressed in Escherichia coli. The purified TAT-GFP fusion protein was able to transduce into the mammalian cells and was found to locate mainly in the cytosol when exogenously added to the cell culture medium. However, using a transfection system, mammalian-expressed TAT-GFP predominantly displayed a nuclear localization and nucleolar accumulation in mammalian cell lines. This discrepancy implies that the exact subcellular localization of transduced protein may depend on cell type, the nature of imported proteins and delivery approach. Taken together, our results demonstrate that a TAT PTD length of 11 amino acids was sufficient to confer protein internalization and its subsequent cellular localization. These novel properties allow these vectors to be useful for studying protein transduction and nuclear import.     

Phosphorylation and activation of a transducible recombinant form of human HSP20 in Escherichia coli

Protein-based cellular therapeutics have been limited by getting molecules into cells and the fact that many proteins require post-translational modifications for activation. Protein transduction domains (PTDs), including that from the HIV TAT protein (TAT), are small arginine rich peptides that carry molecules across the cell membrane. We have shown that the heat shock-related protein, HSP20 is a downstream-mediator of cyclic nucleotide-dependent relaxation of vascular smooth muscle and is activated by phosphorylation. In this study, we co-expressed in Escherichia coli the cDNAs encoding the catalytic subunit of protein kinase G and a TAT-HSP20 fusion protein composed of the TAT PTD (-YGRKKRRQRRR-) fused to the N-terminus of human HSP20. Immunoblot and HPLC-ESI-MS/MS analysis of the purified TAT-HSP20 demonstrated that it was phosphorylated at serine 40 (equivalent to serine 16 in wild-type human HSP20). This phosphorylated TAT-HSP20 was physiologically active in intact smooth muscles in that it inhibited 5-hydroxytryptamine-induced contractions by 57%+/-4.5. The recombinant phosphorylated protein also led to changes in actin cytoskeletal morphology in 3T3 cells. These results delineate strategies for the expression and activation of therapeutic molecules for intracellular protein based therapeutics.     

Tat-mediated protein delivery in living Caenorhabditis elegans

The Tat protein from HIV-1 fused with heterologous proteins traverses biological membranes in a transcellular process called: protein transduction. This has already been successfully exploited in various biological models, but never in the nematode worm Caenorhabditis elegans. TAT-eGFP or GST-eGFP proteins were fed to C. elegans worms, which resulted in the specific localization of Tat-eGFP to epithelial intestinal cells. This system represents an efficient tool for transcellular transduction in C. elegans intestinal cells. Indeed, this approach avoids the use of tedious purification steps to purify the TAT fusion proteins and allows for rapid analyses of the transduced proteins. In addition, it may represent an efficient tool to functionally analyze the mechanisms of protein transduction as well as to complement RNAi/KO in the epithelial intestinal system. To sum up, the advantage of this technology is to combine the potential of bacterial expression system and the Tat-mediated transduction technique in living worm.     

A peptide carrier for the delivery of biologically active proteins into mammalian cells.

The development of peptide drugs and therapeutic proteins is limited by the poor permeability and the selectivity of the cell membrane. There is a growing effort to circumvent these problems by designing strategies to deliver full-length proteins into a large number of cells. A series of small protein domains, termed protein transduction domains (PTDs), have been shown to cross biological membranes efficiently and independently of transporters or specific receptors, and to promote the delivery of peptides and proteins into cells. TAT protein from human immunodeficiency virus (HIV-1) is able to deliver biologically active proteins in vivo and has been shown to be of considerable interest for protein therapeutics. Similarly, the third alpha-helix of Antennapedia homeodomain, and VP22 protein from herpes simplex virus promote the delivery of covalently linked peptides or proteins into cells. However, these PTD vectors display a certain number of limitations in that they all require crosslinking to the target peptide or protein. Moreover, protein transduction using PTD-TAT fusion protein systems may require denaturation of the protein before delivery to increase the accessibility of the TAT-PTD domain. This requirement introduces an additional delay between the time of delivery and intracellular activation of the protein. In this report, we propose a new strategy for protein delivery based on a short amphipathic peptide carrier, Pep-1. This peptide carrier is able to efficiently deliver a variety of peptides and proteins into several cell lines in a fully biologically active form, without the need for prior chemical covalent coupling or denaturation steps. In addition, this peptide carrier presents several advantages for protein therapy, including stability in physiological buffer, lack of toxicity, and lack of sensitivity to serum. Pep-1 technology should be extremely useful for targeting specific protein-protein interactions in living cells and for screening novel therapeutic proteins.     

TAT-mediated delivery of human glutamate dehydrogenase into PC12 cells

Human glutamate dehydrogenase (GDH) gene was fused with a gene fragment encoding the nine amino acid (RKKRRQRRR) protein transduction domain of human immunodeficiency virus TAT protein in bacterial expression vector to produce genetic in-frame TAT-GDH fusion protein. The TAT-GDH protein can enter PC12 cells efficiently when added exogenously in culture media as determined by Western blot analysis and enzyme activities. Once inside the cells, the transduced denatured TAT-GDH protein showed a full activity of GDH indicating that the TAT-GDH fusion protein was correctly refolded after delivery into cells and the activities of GDH in the TAT-GDH fusion protein was not affected by the addition of the TAT sequence. TAT-GDH fusion protein and TAT itself showed no cytotoxicity in PC12 cells. Although the exact mechanism of transduction across a membrane remains unclear, the transduction activity of TAT-GDH into PC12 cells may suggest new possibilities for direct delivery of GDH into the patients with the GDH-deficient disorders.     

Heme oxygenase-1 fused to a TAT peptide transduces and protects pancreatic beta-cells

Transplantation of islets is becoming an established method for treating type 1 diabetes. However, viability of islets is greatly affected by necrosis/apoptosis induced by oxidative stress and other insults during isolation and subsequent in vitro culture. Expression of cytoprotective proteins, such as heme oxygenase-1 (HO-1), reduces the deleterious effects of oxidative stress in transplantable islets. We have generated a fusion protein composed of HO-1 and TAT protein transduction domain (TAT/PTD), an 11-aa cell penetrating peptide from the human immunodeficiency virus TAT protein. Transduction of TAT/PTD-HO-1 to insulin-producing cells protects against TNF-alpha-mediated cytotoxicity. TAT/PTD-HO-1 transduction to islets does not impair islet physiology, as assessed by reversion of chemically induced diabetes in immunodeficient mice. Finally, we report that transduction of HO-1 fusion protein into islets improves islet viability in culture. This approach might have a positive impact on the availability of islets for transplantation.     

TAT-mediated protein transduction and targeted delivery of fusion proteins into mitochondria of breast cancer cells

The protein transduction domain (PTD) from the HIV-1 TAT protein has been widely utilized to deliver biologically active macromolecules, including full-length proteins, into a variety of cell types in vitro and in vivo. Without additional targeting signals, the intracellular localization of the proteins delivered in this fashion appears to be cytoplasmic, nuclear or, as recently reported, endosomal. In this study, we show that the presence of the mitochondrial targeting signal (MTS) from hMnSOD on the N-terminus of TAT-fusion proteins directs them into mitochondria of breast cancer cells. We generated and purified fusion proteins containing GFP (MTS-GFP-TAT) or Exonuclease III (MTS-ExoIII-TAT) from Escherichia coli. The results of Western blots of subcellular fractions and fluorescent microscopic analyses revealed efficient protein transduction and mitochondrial localization of the fusion proteins. Specific exonuclease activity was found in the mitochondrial extracts isolated from MTS-ExoIII-TAT transduced cells. This increased exonuclease activity reduced the repair of mtDNA damage following oxidative stress. This diminished mtDNA repair led to a decrease in survival of breast cancer cells. Thus, the present study demonstrates the applicability of this new approach for intramitochondrial targeting of TAT-fusion proteins capable of modulating mitochondrial function and cell survival.     

一种高效转导蛋白质入哺乳细胞的方法--HIV TAT介导法

HIV TAT介导蛋白质入哺乳细胞的方法1988年就有文献报道，但近年才日趋成熟，且广泛应用于分子生物学研究。传统的调控哺乳细胞的途径有转导目的蛋白的表达型载体、微注射目的蛋白等。与之相比，TAT介导法有操作简单、迅速、应用广泛、可控性强等优点。     

Revised Role of Glycosaminoglycans in TAT Protein Transduction Domain-mediated Cellular Transduction

Cellular uptake of the human immunodeficiency virus TAT protein transduction domain (PTD), or cell-penetrating peptide, has previously been surmised to occur in a manner dependent on the presence of heparan sulfate proteoglycans that are expressed ubiquitously on the cell surface. These acidic polysaccharides form a large pool of negative charge on the cell surface that TAT PTD binds avidly. Additionally, sulfated glycans have been proposed to aid in the interaction of TAT PTD and other arginine-rich PTDs with the cell membrane, perhaps aiding their translocation across the membrane. Surprisingly, however, TAT PTD-mediated induction of macropinocytosis and cellular transduction occurs in the absence of heparan sulfate and sialic acid. Using labeled TAT PTD peptides and fusion proteins, in addition to TAT PTD-Cre recombination-based phenotypic assays, we show that transduction occurs efficiently in mutant Chinese hamster ovary cell lines deficient in glycosaminoglycans and sialic acids. Similar results were obtained in cells where glycans were enzymatically removed. In contrast, enzymatic removal of proteins from the cell surface completely ablated TAT PTD-mediated transduction. Our findings support the hypothesis that acidic glycans form a pool of charge that TAT PTD binds on the cell surface, but this binding is independent of the PTD-mediated transduction mechanism and the induction of macropinocytotic uptake by TAT PTD.