Characterization of a novel cell penetrating peptide derived from human Oct4

Delivered complementation in planta (DCIP) enables measurement of peptide-mediated protein delivery efficiency in plants

Using a fluorescence complementation assay, Delivered Complementation in Planta (DCIP), we demonstrate cell-penetrating peptide-mediated cytosolic delivery of peptides and recombinant proteins in Nicotiana benthamiana. We show that DCIP enables quantitative measurement of protein delivery efficiency and enables functional screening of cell-penetrating peptides for in-planta protein delivery. Finally, we demonstrate that DCIP detects cell-penetrating peptide-mediated delivery of recombinantly expressed proteins such as mCherry and Lifeact into intact leaves. We also demonstrate delivery of a recombinant plant transcription factor, WUSCHEL (AtWUS), into N. benthamiana. RT-qPCR analysis of AtWUS delivery in Arabidopsis seedlings also suggests delivered WUS can recapitulate transcriptional changes induced by overexpression of AtWUS. Taken together, our findings demonstrate that DCIP offers a new and powerful tool for interrogating cytosolic delivery of proteins in plants and highlights future avenues for engineering plant physiology.

Functionalised penetrating peptide-chondroitin sulphate‑gold nanoparticles: Synthesis, characterization, and applications as an anti-Alzheimer's disease drug

The purpose of this study was to construct a transmembrane peptide-chondroitin sulphate‑gold nanoparticle (TAT-CS@Au) delivery system and investigate its activity as an anti-Alzheimer's disease (AD) drug. We successfully prepared TAT-CS@Au nanoparticles, investigated their anti-AD effects, and explored the possible mechanisms in in vitro models. TAT-CS@Au exhibited excellent cellular uptake and transport capacity, effectively inhibited the accumulation of Aβ_1-40, and significantly reduced Aβ_1-40-induced apoptosis in SH-SY5Y cells. Furthermore, TAT-CS@Au significantly reduced oxidative stress damage and cholinergic injury induced by Aβ_1-40 by regulating intracellular concentrations of reactive oxygen species (ROS), malondialdehyde (MDA), glutathione peroxidase (GSH-Px), and acetylcholine (ACh). Western blotting results demonstrated that TAT-CS@Au inhibited aberrant tau phosphorylation (Ser199, Thr205, Ser404, and Ser396) through GSK3β inactivation. TAT-CS@Au decreased the levels of inflammatory factors, specifically TNF-α, IL-6, and IL-1β, by inhibiting NF-κB nuclear translocation by activating MAPK signalling pathways. Overall, these results indicate that TAT-CS@Au exhibits excellent transmembrane ability, inhibits Aβ_1-40 accumulation, antagonises oxidative stress, reduces aberrant tau phosphorylation, and suppresses the expression of inflammatory factors. TAT-CS@Au may be a multi-target anti-AD drug with good cell permeability, providing new insights into the design and research of anti-AD therapeutics.

Antimicrobial and Cell-Penetrating Peptides: Understanding Penetration for the Design of Novel Conjugate Antibiotics

Antimicrobial peptides (AMPs) are short oligopeptides that can penetrate the bacterial inner and outer membranes. Together with cell-penetrating peptides (CPPs), they are called membrane active peptides; peptides which can translocate across biological membranes. Over the last fifty years, attempts have been made to understand the molecular features that drive the interactions of membranes with membrane active peptides. This review examines the features of a membrane these peptides exploit for translocation, as well as the physicochemical characteristics of membrane active peptides which are important for translocation. Moreover, it presents examples of how these features have been used in recent years to create conjugates consisting of a membrane active peptide, called a "vector", attached to either a current or novel antibiotic, called a "cargo" or "payload". In addition, the review discusses what properties may contribute to an ideal peptide vector able to deliver cargoes across the bacterial outer membrane as the rising issue of antimicrobial resistance demands new strategies to be employed to combat this global public health threat.

Cell-penetrating peptides in protein mimicry and cancer therapeutics

Extensive research has been undertaken in the pursuit of anticancer therapeutics. Many anticancer drugs require specificity of delivery to cancer cells, whilst sparing healthy tissue. Cell-penetrating peptides (CPPs), now well established as facilitators of intracellular delivery, have in recent years advanced to incorporate target specificity and thus possess great potential for the targeted delivery of anticancer cargoes. Though none have yet been approved for clinical use, this novel technology has already entered clinical trials. In this review we present CPPs, discuss their classification, mechanisms of cargo internalization and highlight strategies for conjugation to anticancer moieties including their incorporation into therapeutic proteins. As the mainstay of this review, strategies to build specificity into tumor targeting CPP constructs through exploitation of the tumor microenvironment and the use of tumor homing peptides are discussed, whilst acknowledging the extensive contribution made by CPP constructs to target specific protein-protein interactions integral to intracellular signaling pathways associated with tumor cell survival and progression. Finally, antibody/antigen CPP conjugates and their potential roles in cancer immunotherapy and diagnostics are considered. In summary, this review aims to harness the potential of CPP-aided drug delivery for future cancer therapies and diagnostics whilst highlighting some of the most recent achievements in selective delivery of anticancer drugs, including cytostatic drugs, to a range of tumor cells both in vitro and in vivo.

Design and Characterization of a Cell-Penetrating Peptide Derived from the SOX2 Transcription Factor

SOX2 is an oncogenic transcription factor overexpressed in nearly half of the basal-like triple-negative breast cancers associated with very poor outcomes. Targeting and inhibiting SOX2 is clinically relevant as high SOX2 mRNA levels are positively correlated with decreased overall survival and progression-free survival in patients affected with breast cancer. Given its key role as a master regulator of cell proliferation, SOX2 represents an important scaffold for the engineering of dominant-negative synthetic DNA-binding domains (DBDs) that act by blocking or interfering with the oncogenic activity of the endogenous transcription factor in cancer cells. We have synthesized an interference peptide (iPep) encompassing a truncated 24 amino acid long C-terminus of SOX2 containing a potential SOX-specific nuclear localization sequence, and the determinants of the binding of SOX2 to the DNA and to its transcription factor binding partners. We found that the resulting peptide (SOX2-iPep) possessed intrinsic cell penetration and promising nuclear localization into breast cancer cells, and decreased cellular proliferation of SOX2 overexpressing cell lines. The novel SOX2-iPep was found to exhibit a random coil conformation predominantly in solution. Molecular dynamics simulations were used to characterize the interactions of both the SOX2 transcription factor and the SOX2-iPep with FGF4-enhancer DNA in the presence of the POU domain of the partner transcription factor OCT4. Predictions of the free energy of binding revealed that the iPep largely retained the binding affinity for DNA of parental SOX2. This work will enable the future engineering of novel dominant interference peptides to transport different therapeutic cargo molecules such as anti-cancer drugs into cells.

Source and exploration of the peptides used to construct peptide-drug conjugates

Peptide-drug conjugates (PDCs) are a class of novel molecules widely designed and synthesized for delivering payload drugs. The peptide part plays a vital role in the whole molecule, because they determine the ability of the molecules to penetrate the membrane and target to the specific targets. Here, we introduce the source of different kinds of cell-penetrating peptides (CPPs) and cell-targeting peptides (CTPs) that have been used or could be used in constructing PDCs as well as their latest application in delivering drugs. What's more, the approaches of developing CPPs and CTPs and the techniques to discover novel peptides are focused on and summarized in the review. This review aims to help relevant researchers fast understand the research status of peptides in PDCs and carry forward the process of novel peptides discovery.

Cupid, a cell permeable peptide derived from amoeba, capable of delivering GFP into a diverse range of species

Cell permeating peptides (CPPs) are attracting great interest for use as molecular delivery vehicles for the transport of biologically active cargo across the cell membrane. The sequence of a novel CPP sequence, termed ‘Cupid’, was identified from the genome of Dictyostelium discoideum. A Cupid-Green Fluorescent Protein (Cupid-GFP) fusion protein was tested on mammalian, whole plant cells, plant leaf protoplast and fungal cell cultures and observed using confocal microscopy. GFP fluorescence builds up within the cell cytosol in 60 min, demonstrating Cupid-GFP has permeated them and folded correctly into its fluorescent form. Our combined data suggest Cupid can act as a molecular vehicle capable of delivering proteins, such as GFP, into the cytosol of a variety of cells.

Understanding Cell Penetration of Cyclic Peptides

Approximately 75% of all disease-relevant human proteins, including those involved in intracellular protein-protein interactions (PPIs), are undruggable with the current drug modalities (i.e., small molecules and biologics). Macrocyclic peptides provide a potential solution to these undruggable targets because their larger sizes (relative to conventional small molecules) endow them the capability of binding to flat PPI interfaces with antibody-like affinity and specificity. Powerful combinatorial library technologies have been developed to routinely identify cyclic peptides as potent, specific inhibitors against proteins including PPI targets. However, with the exception of a very small set of sequences, the vast majority of cyclic peptides are impermeable to the cell membrane, preventing their application against intracellular targets. This Review examines common structural features that render most cyclic peptides membrane impermeable, as well as the unique features that allow the minority of sequences to enter the cell interior by passive diffusion, endocytosis/endosomal escape, or other mechanisms. We also present the current state of knowledge about the molecular mechanisms of cell penetration, the various strategies for designing cell-permeable, biologically active cyclic peptides against intracellular targets, and the assay methods available to quantify their cell-permeability.

NF-YA enters cells through cell penetrating peptides

Cell Penetrating Peptides -CPPs- are short aminoacidic stretches present in proteins that have the ability to translocate the plasma membrane and facilitate delivery of various molecules. They are usually rich in basic residues, and organized as alpha helices. NF-Y is a transcription factor heterotrimer formed by two Histone Fold Domain -HFD- subunits and the sequence-specific NF-YA. NF-YA possesses two α-helices rich in basic residues. We show that it efficiently enters cells at nanomolar concentrations in the absence of carrier peptides. Mutagenesis identified at least two separate CPPs in the A1 and A2, which overlap with previously identified nuclear localization signals (NLS). The half-life of the transduced protein is short in human cancer cells, longer in mouse C2C12 myoblasts. The internalized NF-YA is capable of trimerization with the HFD subunits and binding to the target CCAAT box. Functionality is further suggested by protein transfection in C2C12 cells, leading to inhibition of differentiation to myotubes. In conclusion, NF-YA contains CPPs, hinting at novel -and unexpected- properties of this subunit.

Cell-Penetrating Function of the Poly(ADP-Ribose) (PAR)-Binding Motif Derived from the PAR-Dependent E3 Ubiquitin Ligase Iduna

Iduna is a poly(ADP-ribose) (PAR)-dependent E3 ubiquitin ligase that regulates cellular responses such as proteasomal degradation and DNA repair upon interaction with its substrate. We identified a highly cationic region within the PAR-binding motif of Iduna; the region was similar among various species and showed amino acid sequence similarity with that of known cell-penetrating peptides (CPPs). We hypothesized that this Iduna-derived cationic sequence-rich peptide (Iduna) could penetrate the cell membrane and deliver macromolecules into cells. To test this hypothesis, we generated recombinant Iduna-conjugated enhanced green fluorescent protein (Iduna-EGFP) and its tandem-repeat form (d-Iduna-EGFP). Both Iduna-EGFP and d-Iduna-EGFP efficiently penetrated Jurkat cells, with the fluorescence signals increasing dose- and time-dependently. Tandem-repeats of Iduna and other CPPs enhanced intracellular protein delivery efficiency. The delivery mechanism involves lipid-raft-mediated endocytosis following heparan sulfate interaction; d-Iduna-EGFP was localized in the nucleus as well as the cytoplasm, and its residence time was much longer than that of other controls such as TAT and Hph-1. Moreover, following intravenous administration to C57/BL6 mice, d-Iduna-EGFP was efficiently taken up by various tissues, including the liver, spleen, and intestine suggesting that the cell-penetrating function of the human Iduna-derived peptide can be utilized for experimental and therapeutic delivery of macromolecules.

Transcription factors: Time to deliver

Transcription factors (TFs) are at the center of the broad regulatory network orchestrating gene expression programs that elicit different biological responses. For a long time, TFs have been considered as potent drug targets due to their implications in the pathogenesis of a variety of diseases. At the same time, TFs, located at convergence points of cellular regulatory pathways, are powerful tools providing opportunities both for cell type change and for managing the state of cells. This task formulation requires the TF modulation problem to come to the fore. We review several ways to manage TF activity (small molecules, transfection, nanocarriers, protein-based approaches), analyzing their limitations and the possibilities to overcome them. Delivery of TFs could revolutionize the biomedical field. Whether this forecast comes true will depend on the ability to develop convenient technologies for targeted delivery of TFs.

HIF1A overexpression using cell-penetrating DNA-binding protein induces angiogenesis in vitro and in vivo

Hypoxia-inducible factor-1 alpha (HIF1A) is an important transcription factor for angiogenesis. Recent studies have used the protein transduction domain (PTD) to deliver genes, but the PTD has not been used to induce the expression of HIF1A. This study aimed at using a novel PTD (Hph-1-GAL4; ARVRRRGPRR) to overexpress the HIF1A and identify the effects on angiogenesis in vitro and in vivo. Overexpression of HIF1A was induced using Hph-1-GAL4 in human umbilical vein/vascular endothelium cells (HUVEC). The expression levels of genes were analyzed by the quantitative real-time polymerase chain reaction (qPCR) after 2 and 4 days, respectively. An in vitro tube formation was performed using Diff-Quik staining. HIF1A and Hph-1-GAL4 were injected subcutaneously into the ventral area of each 5-week-old mouse. All of the plugs were retrieved after 1 week, and the gene expression levels were evaluated by qPCR. Each Matrigel plug was evaluated using the hemoglobin assay and hematoxylin and eosin (HE) staining. The expression levels of HIF1A and HIF1A target genes were significantly higher in HIF1A-transfected HUVEC than in control HUVEC in vitro. In the in vivo Matrigel plug assay, the amount of hemoglobin was significantly higher in the HIF1A-treatment group than in the PBS-treatment group. Blood vessels were identified in the HIF1A-treatment group. The expression levels of HIF1A, vascular endothelial growth factor (Vegf), and Cd31 were significantly higher in the HIF1A-treatment group than in the PBS-treatment group. These findings suggest that using Hph-1-G4D to overexpress HIF1A might be useful for transferring genes and regenerating tissues.

Toxin bioportides: exploring toxin biological activity and multifunctionality

Toxins have been shown to have many biological functions and to constitute a rich source of drugs and biotechnological tools. We focus on toxins that not only have a specific activity, but also contain residues responsible for transmembrane penetration, which can be considered bioportides-a class of cell-penetrating peptides that are also intrinsically bioactive. Bioportides are potential tools in pharmacology and biotechnology as they help deliver substances and nanoparticles to intracellular targets. Bioportides characterized so far are peptides derived from human proteins, such as cytochrome c (CYCS), calcitonin receptor (camptide), and endothelial nitric oxide synthase (nosangiotide). However, toxins are usually disregarded as potential bioportides. In this review, we discuss the inclusion of some toxins and molecules derived thereof as a new class of bioportides based on structure activity relationship, minimization, and biological activity studies. The comparative analysis of the amino acid residue composition of toxin-derived bioportides and their short molecular variants is an innovative analytical strategy which allows us to understand natural toxin multifunctionality in vivo and plan novel pharmacological and biotechnological products. Furthermore, we discuss how many bioportide toxins have a rigid structure with amphiphilic properties important for both cell penetration and bioactivity.

Bacterial membrane binding and pore formation abilities of carbohydrate recognition domain of fish lectin

Antimicrobial peptides (AMPs) are innate molecules that are found in a wide variety of species ranging from bacteria to humans. In recent years, excessive usage of antibiotics resulted in development of multi-drug resistant pathogens which made researchers to focus on AMPs as potential substitute for antibiotics. Lily type mannose-binding lectin is an extended super-family of structurally and evolutionarily related sugar binding proteins. These lectins are well-known AMPs which play important roles in fish defense mechanism. Here, we report a full-length lily type lectin-2 (LTL-2) identified from the cDNA library of striped murrel, Channa striatus (Cs). CsLTL-2 protein contained B-lectin domain along with three carbohydrate binding sites which is a prominent characteristic functional feature of LTL. The mRNA transcripts of CsLTL-2 were predominantly expressed in gills and considerably up-regulated upon infection with fungus (Aphanomyces invadans) and bacteria (Aeromonas hydrophila). To evaluate the antimicrobial activity of the carbohydrate binding region of CsLTL-2, the region was synthesized (QP13) and its bactericidal activity was analyzed. In addition, QP13 was labeled with fluorescein isothiocyanate (FITC) and its binding affinity with the bacterial cell membranes was analyzed. Minimum inhibitory concentration assay revealed that QP13 inhibited the growth of Escherichia coli at a concentration of 80 μM/ml. Confocal microscopic observation showed that FITC tagged QP13 specifically bound to the bacterial membrane. Fluorescence assisted cell sorter (FACS) assay showed that QP13 reduced the bacterial cell count drastically. Therefore, the mechanism of action of QP13 on E. coli cells was determined by propidium iodide internalization assay which confirmed that QP13 induced bacterial membrane disruption. Moreover, the peptide did not show any cytotoxicity towards fish peripheral blood leucocytes. Taken together, these results support the potentiality of QP13 that can be used as an antimicrobial agent against the tested pathogens.

Non-viral methods for generating integration-free, induced pluripotent stem cells

Induced pluripotent stem (iPS) cells were created from mouse fibroblasts by induced expression of Yamanaka factors, Oct3/4, Sox2, Klf4, and c-Myc. This technique has quickly resulted in an exponential increase in the amount of pluripotency studies, and has provided a valuable tool in regenerative medicine. At the same time, many methodologies to generate iPS cells have been reported, and are comprised mainly of viral methods and non-viral methods. Although viral methods may not be applicable for clinical applications, various nonviral methods have been reported in recent years, including DNA vector-based approaches, transfection of mRNA, transduction of reprogramming proteins, and use of small molecule compounds. This review summarizes and evaluates these non-viral methods.

Cell-penetrating peptides transport therapeutics into cells

Nearly 30years ago, certain small, relatively nontoxic peptides were discovered to be capable of traversing the cell membrane. These cell-penetrating peptides, as they are now called, have been shown to not only be capable of crossing the cell membrane themselves but can also carry many different therapeutic agents into cells, including small molecules, plasmid DNA, siRNA, therapeutic proteins, viruses, imaging agents, and other various nanoparticles. Many cell-penetrating peptides have been derived from natural proteins, but several other cell-penetrating peptides have been developed that are either chimeric or completely synthetic. How cell-penetrating peptides are internalized into cells has been a topic of debate, with some peptides seemingly entering cells through an endocytic mechanism and others by directly penetrating the cell membrane. Although the entry mechanism is still not entirely understood, it seems to be dependent on the peptide type, the peptide concentration, the cargo the peptide transports, and the cell type tested. With new intracellular disease targets being discovered, cell-penetrating peptides offer an exciting approach for delivering drugs to these intracellular targets. There are hundreds of cell-penetrating peptides being studied for drug delivery, and ongoing studies are demonstrating their success both in vitro and in vivo.

Drug delivery strategies to enhance the permeability of the blood-brain barrier for treatment of glioma

Gliomas are amongst the most insidious and destructive types of brain cancer and are associated with a poor prognosis, frequent recurrences, and extremely high lethality despite combination treatment of surgery, radiotherapy, and chemotherapy. The existence of the blood–brain barrier (BBB) restricts the delivery of therapeutic molecules into the brain and offers the clinical efficacy of many pharmaceuticals that have been demonstrated to be effective for other kinds of tumors. This challenge emphasizes the need to be able to deliver drugs effectively across the BBB to reach the brain parenchyma. Enhancement of the permeability of the BBB and being able to transport drugs across it has been shown to be a promising strategy to improve drug absorption and treatment efficacy. This review highlights the innovative technologies that have been introduced to enhance the permeability of the BBB and to obtain an optimal distribution and concentration of drugs in the brain to treat gliomas, such as nanotechniques, hyperthermia techniques, receptor-mediated transport, cell-penetrating peptides, and cell-mediated delivery.

Penetratin Story: An Overview

Cell-penetrating peptides are short, often hydrophilic peptides that get access to the intracellular milieu. They have aroused great interest both in academic and applied research. First, cellular internalization of CPPs often involves the crossing of a biological membrane (plasma or vesicular), thus challenging the view of the non-permeability of these structures to large hydrophilic molecules. Secondly, CPPs can drive the internalization of hydrophilic cargoes into cells, a rate-limiting step in the development of many therapeutic substances. Interestingly, the two most used CPPs, TAT and penetratin peptides, are derived from natural proteins, HIV Tat and Antennapedia homeoprotein, respectively. The identification of the penetratin peptide, summarized in this review, is intimately linked to the study of its parental natural protein.

OCT4: A penetrant pluripotency inducer

Native OCT4 protein has the intrinsic ability of crossing cellular membranes to enter cells. This finding could revive efforts to induce pluripotency with proteins replacing nucleic acid-based approaches, and raises the intriguing question as to whether OCT4 can act non-cell-autonomously.