Jean-Luc Lenormand

Liposomes-mediated delivery of pro-apoptotic therapeutic membrane proteins

The delivery of functional therapeutic proteins by lipid vesicles into targeted living cells is one of the most promising strategies for treatment of different diseases and cancer. The use of this system in the delivery of membrane proteins directly into cells remains to be tested because the methods for producing membrane proteins are difficult to perform. Here we describe the effect of proteoliposomes containing the voltage-dependent anion channel (VDAC) and pro-apoptotic Bak, both produced with an optimized cell-free expression system. For the first time, recombinant VDAC and Bak proteins are synthesized and directly integrated into the lipidic bilayer of natural liposomes in a one-step reaction. VDAC has been shown to play an essential role in apoptosis in mammalian cells by regulating cytochrome c release from mitochondria and Bak modulates mitochondrial membrane permeability upon activation. Internalization of recombinant proteoliposomes into mammalian cells induces apoptosis by release of cytochrome c and caspases activation. These results highlight that membrane proteins integrated in natural liposomes can represent an excellent candidate for cancer protein therapy.

Production of membrane proteins using cell-free expression systems.

Different overexpression systems are widely used in the laboratory to produce proteins in a reasonable amount for functional and structural studies. However, to optimize these systems without modifying the cellular functions of the living organism remains a challenging task. Cell-free expression systems have become a convenient method for the high-throughput expression of recombinant proteins, and great effort has been focused on generating high yields of proteins. Furthermore, these systems represent an attractive alternative for producing difficult-to-express proteins, such as membrane proteins. In this review, we highlight the recent improvements of these cell-free expression systems and their direct applications in the fields of membrane proteins production, protein therapy and modern proteomics.

The translational factor eIF3f: the ambivalent eIF3 subunit

The regulation of the protein synthesis has a crucial role in governing the eukaryotic cell growth. Subtle changes of proteins involved in the translation process may alter the rate of the protein synthesis and modify the cell fate by shifting the balance from normal status into a tumoral or apoptotic one. The largest eukaryotic initiation factor involved in translation regulation is eIF3. Amongst the 13 factors constituting eIF3, the f subunit finely regulates this balance in a cell-type-specific manner. Loss of this factor causes malignancy in several cells, and atrophy in normal muscle cells. The intracellular interacting partners which influence its physiological significance in both cancer and muscle cells are detailed in this review. By delineating the global interaction network of this factor and by clarifying its intracellular role, it becomes apparent that the f subunit represents a promising candidate molecule to use for biotherapeutic applications.

Characterization of the Cell-penetrating Properties of the Epstein-Barr Virus ZEBRA trans-Activator

The Epstein-Barr virus basic leucine zipper transcriptional activator ZEBRA was shown recently to cross the outer membrane of live cells and to accumulate in the nucleus of lymphocytes. We investigated the potential application of the Epstein-Barr virus trans-activator ZEBRA as a transporter protein to facilitate transduction of cargo proteins. Analysis of different truncated forms of ZEBRA revealed that the minimal domain (MD) required for internalization spans residues 170–220. MD efficiently transported reporter proteins such as enhanced green fluorescent protein (EGFP) and β-galactosidase in several normal and tumor cell lines. Functionality of internalized cargo proteins was confirmed by β-galactosidase activity in transduced cells, and no MD-associated cell toxicity was detected. Translocation of MD through the cell membrane required binding to cell surface-associated heparan sulfate proteoglycans as shown by strong inhibition of protein uptake in the presence of heparin. We found that internalization was blocked at 4 °C, whereas no ATP was required as shown by an only 25% decreased uptake efficiency in energy-depleted cells. Common endocytotic inhibitors such as nystatin, chlorpromazine, and wortmannin had no significant impact on MD-EGFP uptake. Only methyl-β-cyclodextrin inhibited MD-EGFP uptake by 40%, implicating the lipid raft-mediated endocytotic pathway. These data suggest that MD-reporter protein transduction occurs mostly via direct translocation through the lipid bilayer and not by endocytosis. This mechanism of MD-mediated internalization is suitable for the efficient delivery of biologically active proteins and renders ZEBRA-MD a promising candidate for therapeutic protein delivery applications.

In Vivo Delivery of Antigens by Adenovirus Dodecahedron Induces Cellular and Humoral Immune Responses to Elicit Antitumor Immunity

Cancer vaccines based on virus-like particles (VLPs) vectors may offer many advantages over other antigen-delivery systems and represent an alternative to the ex vivo cell therapy approach. In this study, we describe the use of penton-dodecahedron (Pt-Dd) VLPs from human adenovirus type 3 (Ad3) as cancer vaccine vehicle for specific antigens, based on its unique cellular internalization properties. WW domains from the ubiquitin ligase Nedd4 serve as an adapter to bind the antigen to Pt-Dd. By engineering fusion partners of WW with the model antigen ovalbumin (OVA), Pt-Dd can efficiently deliver WW-OVA in vitro and the Pt-Dd/WW complex can be readily internalized by dendritic cells (DCs). Immunization with WW-OVA/Pt-Dd results in 90% protection against B16-OVA melanoma implantation in syngeneic mice. This high level of protection correlates with the development of OVA-specific CD8(+) T cells. Moreover, vaccination with WW-OVA Pt-Dd induces robust humoral responses in mice as shown by the high levels of anti-OVA antibodies (Abs) detected in serum. Importantly, treatment of mice bearing B16-OVA tumors with WW-OVA/Pt-Dd results in complete tumor regression in 100% of cases. Thus, our data supports a dual role of Pt-Dd as antigen-delivery vector and natural adjuvant, able to generate integrated cellular and humoral responses of broad immunogenic complexity to elicit specific antitumor immunity. Antigen delivery by Pt-Dd vector is a promising novel strategy for development of cancer vaccines with important clinical applications.

A Bacterial Cell‐Free Expression System to Produce Membrane Proteins and Proteoliposomes: From cDNA to Functional Assay

Limitations in the production of folded membrane proteins represent the major bottleneck for functional and structural studies of this huge category of macromolecules. Cell‐free expression systems provide an attractive alternative to the classical overexpression systems for producing membrane proteins. However, optimization of these systems remains a challenging task, considering the hydrophobic properties of these molecules. This unit describes the production of eukaryotic membrane proteins either in soluble form or integrated into liposomes using a bacterial cell‐free expression system. Liposomes in the reaction mixture induce the direct insertion of freshly produced membrane proteins into the bilayer and allow the formation of functional proteoliposomes in which the membrane proteins are correctly folded. Curr. Protoc. Protein Sci. 54:5.22.1‐5.22.30.

ZEBRA cell-penetrating peptide as an efficient delivery system in Candida albicans

There is increasing interest in drug delivery systems, such as nanoparticles, liposomes, and cell‐penetrating peptides, for the development of new antimicrobial treatments. In this study, we investigated the transduction capacity of a carrier peptide derived from the Epstein–Barr virus ZEBRA protein in the pathogenic fungus Candida albicans. ZEBRA‐minimal domain (MD) was able to cross the cell wall and cell membrane, delivering eGFP to the cytoplasm. Uptake into up to 70% of the cells was observed within two hours, without toxicity. This new delivery system could be used in C. albicans as a carrier for different biological molecules including peptides, proteins, and nucleic acids. Thereby, in antifungal therapy, MD may carry promising bioactive fungal inhibitors that otherwise penetrate poorly into the cells. Furthermore, MD will be of interest for deciphering molecular pathways involving cell‐cycle control in yeast or signaling pathways. Short interfering peptides could be internalized using MD, providing new tools for the inhibition of metabolic or signaling cascades essential for the growth and virulence of C. albicans, such as yeast‐to‐hyphae transition, cell wall remodeling, stress signaling and antifungal resistance. These findings create new possibilities for the internalization of cargo molecules, with applications for both treatment and functional analyses.

Single-step production of functional OEP24 proteoliposomes.

The pea chloroplastic outer envelope protein OEP24 is a voltage-dependent channel that can function as a general solute channel in plants. OEP24 is a close functional homologue of VDAC which, in mammalian cells, modulates the permeability of the outer mitochondrial membrane. Here, we describe the production in a one-step reaction of active OEP24 in proteoliposomes or in soluble form using a cell-free expression system. We combine evidence from electrophysiological experiments, biophysical characterization, and biochemical analysis demonstrating that OEP24 is present as a functional channel in liposomes. Thus, production of OEP-containing proteoliposomes may provide a helpful tool for deciphering the role of the OEP family members.

Functional characterization of p7 viroporin from hepatitis C virus produced in a cell-free expression system.

Using a cell-free expression system we produced the p7 viroporin embedded into a lipid bilayer in a single-step manner. The protein quality was assessed using different methods. We examined the channel forming activity of p7 and verified its inhibition by 5-(N,N-Hexamethylene) amiloride (HMA). Fourier transformed infrared spectroscopy (FTIR) experiments further showed that when p7 was inserted into synthetic liposomes, the protein displayed a native-like conformation similar to p7 obtained from other sources. Photoactivable amino acid analogs used for p7 protein synthesis enabled oligomerization state analysis in liposomes by cross-linking. Therefore, these findings emphasize the quality of the cell-free produced p7 proteoliposomes which can benefit the field of the hepatitis C virus (HCV) protein production and characterization and also provide tools for the development of new inhibitors to reinforce our therapeutic arsenal against HCV.

Recombinant Nox4 cytosolic domain produced by a cell or cell-free base systems exhibits constitutive diaphorase activity

The membrane protein NADPH (nicotinamide adenine dinucleotide phosphate) oxidase Nox4 constitutively generates reactive oxygen species differing from other NADPH oxidases activity, particularly in Nox2 which needs a stimulus to be active. Although the precise mechanism of production of reactive oxygen species by Nox2 is well characterized, the electronic transfer throughout Nox4 remains unclear. Our study aims to investigate the initial electronic transfer step (diaphorase activity) of the cytosolic tail of Nox4. For this purpose, we developed two different approaches to produce soluble and active truncated Nox4 proteins. We synthesized soluble recombinant proteins either by in vitro translation or by bacteria induction. While proteins obtained by bacteria induction demonstrate an activity of 4.4 ± 1.7 nmol/min/nmol when measured against iodonitro tetrazolium chloride and 20.5 ± 2.8 nmol/min/nmol with cytochrome c, the soluble proteins produced by cell-free expression system exhibit a diaphorase activity with a turn-over of 26 ± 2.6 nmol/min/nmol when measured against iodonitro tetrazolium chloride and 48 ± 20.2 nmol/min/nmol with cytochrome c. Furthermore, the activity of the soluble proteins is constitutive and does not need any stimulus. We also show that the cytosolic tail of the isoform Nox4B lacking the first NADPH binding site is unable to demonstrate any diaphorase activity pointing out the importance of this domain.