Cloning, expression, purification and functional characterization of the oligomerization domain of Bcr–Abl oncoprotein fused to the cytoplasmic transduction peptide

Strategies for Optimizing the Production of Proteins and Peptides with Multiple Disulfide Bonds

Bacteria can produce recombinant proteins quickly and cost effectively. However, their physiological properties limit their use for the production of proteins in their native form, especially polypeptides that are subjected to major post-translational modifications. Proteins that rely on disulfide bridges for their stability are difficult to produce in Escherichia coli. The bacterium offers the least costly, simplest, and fastest method for protein production. However, it is difficult to produce proteins with a very large size. Saccharomyces cerevisiae and Pichia pastoris are the most commonly used yeast species for protein production. At a low expense, yeasts can offer high protein yields, generate proteins with a molecular weight greater than 50 kDa, extract signal sequences, and glycosylate proteins. Both eukaryotic and prokaryotic species maintain reducing conditions in the cytoplasm. Hence, the formation of disulfide bonds is inhibited. These bonds are formed in eukaryotic cells during the export cycle, under the oxidizing conditions of the endoplasmic reticulum. Bacteria do not have an advanced subcellular space, but in the oxidizing periplasm, they exhibit both export systems and enzymatic activities directed at the formation and quality of disulfide bonds. Here, we discuss current techniques used to target eukaryotic and prokaryotic species for the generation of correctly folded proteins with disulfide bonds.

Biological characteristics of renal cancer cells after CTP-mediated cancer suppressor gene NPRL2 protein treatment

Nitrogen permease regulator like-2 (NPRL2) has been proved to be a useful suppressor gene in treating many cancers containing renal cancer based on experiments. Transgenic technology which transfect exogenous NPRL2 gene into cancer cell was used in these experiments. However, this technology has defects, such as gene mutation and loss. Cytoplasmic transduction peptide (CTP) can be used to avoid these defects because it can directly mediate proteins to penetrate cell membrane and specifically locate in cytoplasm. In this article, CTP was used to directly mediate NPRL2 protein into the renal cancer cell line 786-O, then cell proliferation was detected by the CCK-8 method, cell cycle and apoptosis were detected by flow cytometry, cell invasion and migration ability were detected by the Transwell assay. Bcl-xl, Cyt-c and caspase-3 were detected by real-time fluorescent quantitative PCR and Western blot for the analysis of the related mechanism. The result showed that CTP successfully mediated NPRL2 protein into renal cancer cells and the growth of cells was significantly inhibited. The mechanism may be NPRL2 down-regulating the expression of Bcl-xl which can up-regulate Cyt-c and further activate caspase-3, and then a cascade reaction is caused for cell apoptosis on the classic mitochondrial apoptosis pathway.

Cell-penetrating fusion peptides OD1 and OD2 interact with Bcr-Abl and influence the growth and apoptosis of K562 cells

The Bcr-Abl oncoprotein is the cause of chronic myelogenous leukemia (CML). Crystal structure analysis suggests that Bcr30-63 is the core of the Bcr-Abl oligomerization interface for aberrant kinase activity; however, the precise role of other residues of Bcr1-72 excluding Bcr30-63 have not been evaluated. In this study, Bcr30-63 was named OD2 and other residues of Bcr1-72 were named OD1. Cytoplasmic transduction peptide (CTP) was used to carry molecules into cytoplasm. CTP-OD1 and CTP-OD2 fusion peptides were expressed from a cold-inducible expression system. Our results demonstrated that both fusion peptides could localize into the cytoplasm, specifically interact with the Bcr-Abl protein and further inhibit growth, induce apoptosis, and decrease the phosphorylation of Bcr-Abl in K562 cell lines. However, the viability of THP-1, a Bcr-Abl negative cell line, was unaffected. These results suggested that CTP-OD1 and CTP-OD2 may be an attractive therapeutic option to inhibit the activation of Bcr-Abl kinase in CML.

Construction and development of a mammalian cell-based full-length antibody display library for targeting hepatocellular carcinoma

We present a detailed method for constructing a mammalian cell-based full-length antibody display library for targeting hepatocellular carcinoma. Two novel mammalian library vectors pcDNA3-CHm and pcDNA3-CLm were constructed that contained restriction enzyme sites NheI, ClaI and antibody constant domain. Mammalian expression vector pcDNA3-CHm contains IgG heavy-chain (HC) constant region and glycosylphosphatidylinositol anchor (GPI) that could be anchored full-length antibodies on the surface of mammalian cells. GOLPH2 prokaryotic expression vector was carried out in Escherichia coli and purified by immobilized metal affinity chromatography. Variable domain of heavy-chain and variable domain of light-chain genes were respectively inserted into the vector pcDNA3-CHm and pcDNA3-CLm by ligation, and antibody libraries are displayed as whole IgG molecules on the cell surface by co-transfecting this HC-GPI with a light chain. By screening the cell library using magnetic beads and cell ELISA, the cell clone that displayed GOLPH2-specific antibodies on cell surfaces was identified. The mammalian cell-based antibody display library is a great potential application for displaying full-length functional antibodies of targeting hepatocellular carcinoma on the surface of mammalian cells. Anti-GOLPH2 display antibody was successfully isolated from the library.

Disruption of Bcr-Abl coiled coil oligomerization by design

Oligomerization is an important regulatory mechanism for many proteins, including oncoproteins and other pathogenic proteins. The oncoprotein Bcr-Abl relies on oligomerization via its coiled coil domain for its kinase activity, suggesting that a designed coiled coil domain with enhanced binding to Bcr-Abl and reduced self-oligomerization would be therapeutically useful. Key mutations in the coiled coil domain of Bcr-Abl were identified that reduce homo-oligomerization through intermolecular charge-charge repulsion yet increase interaction with the Bcr-Abl coiled coil through additional salt bridges, resulting in an enhanced ability to disrupt the oligomeric state of Bcr-Abl. The mutations were modeled computationally to optimize the design. Assays performed in vitro confirmed the validity and functionality of the optimal mutations, which were found to exhibit reduced homo-oligomerization and increased binding to the Bcr-Abl coiled coil domain. Introduction of the mutant coiled coil into K562 cells resulted in decreased phosphorylation of Bcr-Abl, reduced cell proliferation, and increased caspase-3/7 activity and DNA segmentation. Importantly, the mutant coiled coil domain was more efficacious than the wild type in all experiments performed. The improved inhibition of Bcr-Abl through oligomeric disruption resulting from this modified coiled coil domain represents a viable alternative to small molecule inhibitors for therapeutic intervention.

The nuclear translocation assay for intracellular protein-protein interactions and its application to the Bcr coiled-coil domain

Protein interactions are critical for normal biological processes and molecular pathogenesis. While it is important to study these interactions, there are limited assays that are performed inside the cell, in the native cell environment, where the majority of protein-protein interactions take place. Here we present a method of studying protein interactions intracellularly using one protein of interest fused to a localization-controllable enhanced GFP (EGFP) construct and the other protein of interest fused to the red fluorescent protein, DsRed. Nuclear translocation of the EGFP construct is induced by addition of a ligand, and the difference in nuclear localization between the induced and noninduced states of the DsRed construct provides an indication of the interaction between the two proteins. This assay, the nuclear translocation assay (NTA), is introduced here as broadly applicable for studying protein interactions in the native environment inside cells and is demonstrated using forms of the coiled-coil domain from the breakpoint cluster region (Bcr) protein.

Expression and functional characterization of platelet-derived growth factor receptor-like gene

AIM: To investigate the role of platelet-derived growth factor receptor-like gene (PDGFRL) in the anti-cancer therapy for colorectal cancers (CRC).

METHODS: PDGFRL mRNA and protein levels were measured by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in CRC and colorectal normal tissues. PDGFRL prokaryotic expression vector was carried out in Escherichia coli (E. coli), and purified by immobilized metal affinity chromatography. The effect of PDGFRL protein on CRC HCT-116 cells was detected by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT), clone counting, cell cycle, and wound healing assay.

RESULTS: Both RT-PCR and immunohistochemistry showed that the expression of PDGFRL in colorectal normal tissues was higher than in cancer tissues. Recombinant pET22b-PDGFRL prokaryotic expression vector was successfully expressed in E. coli, and the target protein was expressed in the form of inclusion bodies. After purification and refolding, recombinant human PDGFRL (rhPDGFRL) could efficiently inhibit the proliferation and invasion of CRC HCT-116 cells detected by MTT, clone counting and wound healing assay. Moreover, rhPDGFRL arrested HCT-116 cell cycling at the G0/G1 phase.

CONCLUSION: PDGFRL is a potential gene for application in the anti-cancer therapy for CRC.

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.

Cloning, expression, purification, distribution and kinetics characterization of the bacterial beta-galactosidase fused to the cytoplasmic transduction peptide in vitro and in vivo

Cytoplasmic transduction peptide (CTP) offers exciting therapeutic opportunities for the treatment of many diseases caused by cytoplasmic functional molecules. It can transduce large, biologically active proteins into the cytoplasmic compartment of several mammalian cells. However, other intriguing features of CTP, including its activity in vitro, and distribution and tissue infiltration abilities in vivo, remain to be explored. The present study was initiated to (1) further confirm the cytoplasmic localization preference and the enzymatic activity of the transduced CTP-beta-gal in vitro and (2) examine the kinetics and tissue distribution of the CTP-beta-gal fusion protein in mice. A CTP-beta-gal fusion protein was expressed in Escherichia coli and either transduced into BaF3-BCR/ABL cells or administered intravenously into female Balb/C mice at a dose of 100 microg per mouse. Its localization in BaF3-BCR/ABL cells was evaluated by immunocytochemistry and in situ X-gal staining, and its distribution in various tissues was analyzed both by in situ X-gal staining and quantitative enzymatic activity assay. beta-Galactosidase enzyme activity was observed in BaF3-BCR/ABL cells and in all tissues tested, with peak activity occurring at 15 min in most tissues and at 24h in brain. These data will not only allow rational selection of delivery schedules for therapeutic CTP, but will also aid the use of CTP fusion protein transduction in the development of protein therapeutics targeting the cytoplasmic compartment both in vitro and in vivo.