Applications, and efficient large-scale production, of recombinant human epidermal growth factor

Economic optimization of expression of soluble human epidermal growth factor in Escherichia coli

Human epidermal growth factor (hEGF) has multiple biological functions, such as promoting cell proliferation, differentiation, and migration. In addition, it is a very expensive polypeptide with attractive market prospects. However, the production of hEGF needs for high cost to manufacture polypeptide demands reinvestigations of process conditions so as to enhance economic benefits. Improving the expression of soluble hEGF is the fundamental method to reduce the cost. In this study, a non-extracellular engineered strain of expressed hEGF was constructed, using plasmid pET-22b(+) in Escherichia coli. Preliminary fermentation and high cell density cultivation were carried out in shake flasks and in a 5 L bioreactor, respectively. A high yield of 98 ± 10 mg/L of soluble hEGF and a dry cell weight (DCW) of 6.98 ± 0.3 g/L were achieved in shake flasks. Then, fermentation conditions were optimized for large-scale production, while taking into consideration the expensive equipment required for cooling and conforming to industrial standards. A yield of 285 ± 10 mg/L of soluble hEGF, a final cell density of 57.4 ± 2 g/L DCW (OD₆₀₀ 141.1 ± 4.9), and hEGF productivity of 14.3 mg/L/h were obtained using a bioreactor at 32 °C for 20 h. The production method developed in this study for the biosynthesis of soluble hEGF is efficient and inexpensive.

T cell resistance to activation by dendritic cells requires long-term culture in simulated microgravity

Immune impairment mediated by microgravity threatens the success of space exploration requiring long-duration spaceflight. The cells of most concern, T lymphocytes, coordinate the host response against microbial and cancerous challenges leading to elimination and long-term protection. T cells are activated upon recognition of specific microbial peptides bound on the surface of antigen presenting cells, such as dendritic cells (DC). Subsequently, this engagement results in T cell proliferation and differentiation into effector T cells driven by autocrine interleukin-2 (IL-2) and other cytokines. Finally, the effector T cells acquire the weaponry needed to destroy microbial invaders and tumors. Studies conducted on T cells during spaceflight, or using Earth-based culture systems, have shown reduced production of cytokines, proliferation and effector functions as compared to controls. This may account for the cases of viral reactivation events and opportunistic infections associated with astronauts of numerous missions. This work has largely been based upon the outcome of T cell activation by stimulatory factors that target select T cell signaling pathways rather than the complex, signaling events related to the natural process of antigen presentation by DC. This study tested the response of an ovalbumin peptide-specific T cell line, OT-II TCH, to activation by DC when the T cells were cultured 24-120 h in a simulated microgravity (SMG) environment generated by a rotary cell culture system. Following 72 h culture of T cells in SMG (SMG-T) or control static (Static-T) conditions, IL-2 production by the T cells was reduced in SMG-T cells compared to Static-T cells upon stimulation by phorbol 12-myristate 13-acetate (PMA) and ionomycin. However, when the SMG-T cells were stimulated with DC and peptide, IL-2 was significantly increased compared to Static-T cells. Such enhanced IL-2 production by SMG-T cells peaked at 72 h SMG culture time and decreased thereafter. When activation of SMG-T cells occurred in SMG, the T cells produced less IL-2 than control T cell cultures upon incubation with PMA and ionomycin. Short-term (24 h) SMG culture and activation of T cells by DC resulted in enhanced IL-2 production compared to Static-T cells, however, when culture was extended to 120 h, SMG-T cells secreted significantly less IL-2 than Static-T cells. SMG-T cell IL-2 doubled upon stimulation of the DC prior to addition to the T cell culture but remained less than control. SMG-T cell resistance to activation appeared comparable to the phenomenon of T cell exhaustion observed in patients with chronic diseases or persistent tumors. That is, long-term culture of T cells in SMG resulted in increased expression of the inhibitory receptor, CTLA-4. Blockade of CTLA-4 interaction with DC ligands resulted in improved T cell IL-2 production. Overall, this is the first study to determine the efficacy of DC in activating peptide-specific T cells. Furthermore, the findings suggests that countermeasures to restore T cell responsiveness in astronauts during long-term spaceflight or those living in microgravity environments should target possible inhibitory pathways that arise on activated T cells following stimulation.

Application of an E. coli signal sequence as a versatile inclusion body tag

Background

Heterologous protein production in Escherichia coli often suffers from bottlenecks such as proteolytic degradation, complex purification procedures and toxicity towards the expression host. Production of proteins in an insoluble form in inclusion bodies (IBs) can alleviate these problems. Unfortunately, the propensity of heterologous proteins to form IBs is variable and difficult to predict. Hence, fusing the target protein to an aggregation prone polypeptide or IB-tag is a useful strategy to produce difficult-to-express proteins in an insoluble form.

Results

When screening for signal sequences that mediate optimal targeting of heterologous proteins to the periplasmic space of E. coli, we observed that fusion to the 39 amino acid signal sequence of E. coli TorA (ssTorA) did not promote targeting but rather directed high-level expression of the human proteins hEGF, Pla2 and IL-3 in IBs. Further analysis revealed that ssTorA even mediated IB formation of the highly soluble endogenous E. coli proteins TrxA and MBP. The ssTorA also induced aggregation when fused to the C-terminus of target proteins and appeared functional as IB-tag in E. coli K-12 as well as B strains. An additive effect on IB-formation was observed upon fusion of multiple ssTorA sequences in tandem, provoking almost complete aggregation of TrxA and MBP. The ssTorA-moiety was successfully used to produce the intrinsically unstable hEGF and the toxic fusion partner SymE, demonstrating its applicability as an IB-tag for difficult-to-express and toxic proteins.

Conclusions

We present proof-of-concept for the use of ssTorA as a small, versatile tag for robust E. coli-based expression of heterologous proteins in IBs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0662-4) contains supplementary material, which is available to authorized users.

A revolutionary approach facilitating co-expression of authentic human epidermal growth factor and basic fibroblast growth factor in both cytoplasm and culture medium of Escherichia coli

During secretory or excretory production of heterologous proteins in Escherichia coli, peptidase processing cleaves the signal peptide off from a premature protein, which is then secreted as a mature product. Many proteins have been successfully expressed as secreted/excreted products in E. coli. However, basic fibroblast growth factor (bFGF), despite its suitability for secretory/excretory production in E. coli, has never been successfully expressed using such an approach. In this communication, we report the application of a revolutionary E. coli system to the efficient expression of not only bFGF, but also human epidermal growth factor (EGF) concurrently, as authentic products in the culture supernatant (SN). More interestingly, both polypeptides were also shown to be present at high levels as authentic products in the cell lysate (CL). The manifestation of this unusual phenomenon required a collaborative action between construct pWKW2, an efficient excretion vector engineered by our group to facilitate extracellular production of EGF, and the Sce VMA intein, which enables self-cleavage of protein sequences fused to it. Both bFGF and EGF derived from SN and CL were characterized to be bioactive. Moreover, despite employing only shake-flask cultivation, the total yields of bFGF and EGF recovered from both SN and CL were impressive, amounting to 103 and 74 mg l(-1) of culture, respectively. The novel expression approach introduced herein may prove to be practically useful for the production of a wide range of proteins in the future.

Diselenides as universal oxidative folding catalysts of diverse proteins

Small-molecule diselenides show considerable potential as catalysts of oxidative protein folding. To explore their scope, diselenide-containing redox buffers were used to promote the folding of proteins that varied in properties such as size, overall tertiary structure, number of disulfide bonds, pI value, and difficulty of in vitro folding. Diselenides are able to catalyze the oxidative folding of all proteins tested, providing significant increases in both rate and yield relative to analogous disulfides. Compared to the disulfide-linked dimer of glutathione (the most commonly used oxidant for in vitro protein folding), selenoglutathione provided markedly improved efficiencies in the folding of biotechnologically important proteins such as hirudin, lysozyme, human epidermal growth factor and interferon α-2a. Selenoglutathione also enhances the renaturation of more challenging targets such as bovine serum albumin, whose native state contains 17 disulfide bonds, and the Fab fragment of an antibody. In the latter case, micromolar amounts of selenoglutathione are able to match the modest yield provided by a previously optimized redox buffer, which contains millimolar levels of glutathione. Taken together, the folding reactions of these diverse proteins exemplify the advantages and limitations of diselenide catalysts.

The efficacy and safety of epidermal growth factor in treatment of diabetic foot ulcers: the preliminary results

OBJECTIVE

To evaluate the efficacy and safety of recombinant human epidermal growth factor (rh-EGF) in healing foot ulcers in diabetic patients.

METHODS

A total of 28 subjects with foot ulcers were recruited into the pilot study. Patients who had obvious peripheral arterial disease, trans-tibial amputation, plastic surgery or skin flap, and skin graft were excluded. The properly debrided wounds and the non closure wounds after toe amputation were included. When the wounds became clean or uninfected, they received twice-a-day treatment with 0.005% Easyef and hydrocolloid dressing. The size and severity of the wounds were evaluated. Others such as blood sugar, renal and hepatic function, serum albumin, vascular condition, foot infection or osteomyelitis were assessed.

RESULTS

All of 28 patients had positive response of granulation (100%). Complete healing was noted in 13 out of 23 subjects and finished 8-week follow-up (56.5%). The rates of wound closure were 43.3%, 59.9%, 68.7%, and 84.8% in week 2, 4, 6 and 8, respectively, regardless of the severity. Being dropped out, three patients needed further interventions. No skin allergic reaction. Over-granulation was observed in one female patient (3.7%), but as minor.

CONCLUSIONS

Easyef has positive effects on healing of moderate-to-severe foot ulcers and demonstrated being safe to diabetic patients. The drug had high tolerability and compliance.

A two-stage refinement approach for the enhancement of excretory production of an exoglucanase from Escherichia coli

Hyper-expression of a secretory exoglucanase, Exg, encoded by the cex gene of Cellulomonas fimi was previously shown to saturate the SecYEG pathway and result in dramatic cell death of recombinant Escherichia coli (Z.B. Fu, K.L. Ng, T.L. Lam, W.K.R. Wong, Cell death caused by hyper-expression of a secretory exoglucanase in Esherichia coli, Protein Expr. Purif. 42 (2005) 67-77). We propose here that the cell lysate ratio (Pre/Mat RQ) of the unprocessed precursor Exg protein (Pre-Exg) and its processed mature product (Mat-Exg) reflects the capacity of E. coli to secrete Exg. A Pre/Mat RQ of 20/80, designated the "Critical Value," was an important threshold measurement. A rise in the Pre/Mat RQ triggered a mass killing effect. The use of various secretion signal peptides did not improve the viability of cells expressing high levels of Pre-Exg under strong tac promoter control. However, use of the weaker vegG promoter in conjunction with a change in start codon of the spa leader sequence from ATG to TTG in a pM1vegGcexL plasmid construct resulted in a high level (0.9 U ml(-1)) of excreted Exg in shake-flask cultures. This was 50% higher than the best result obtained from plasmid construct lacUV5par8cex, using the lacUV5 promoter and the ompA leader sequence. Variations in the excreted Exg activities were attributable to differences in the Pre/Mat RQ values of the induced cultures harboring pM1vegGcexL and lacUV5par8cex. These values were 18/82 and 10/90, respectively. Employing fed-batch cultivation in two-liter fermentors, an induced JM101(pM1vegGcexL) culture yielded 4.5 U ml(-1) of excreted Exg, which was over six fold greater that previously reported. Our results illustrate the successful application of the Pre/Mat RQ ratio as a guide to the attainment of a maximum level of secreted/excreted Exg.

Cell death caused by hyper-expression of a secretory exoglucanase in Escherichia coli

Induced expression of a gene fusion between the ompA leader sequence and the Cellulomonas fimi cex gene encoding a secretory exoglucanase, Exg, engineered in the Tac-cassette excretion vector was lethal to Escherichia coli. An exponentially growing culture harboring the recombinant construct suffered slow growth and 99.9% of its cells died within 60-100 min after induction. This abnormality was found to have a close correlation with the rapid increase in the relative amount of the OmpA/Exg fusion precursor (Pre-Exg) compared to its processed product (Mat-Exg). Analysis of subcellular fractions revealed the presence of Pre-Exg in the inner membrane of cultures expressing high levels but not low levels of Pre-Exg. As only Pre-Exg but not Mat-Exg was detectable in the cytoplasm, and Exg was shown by cross-linking experiments to be physically associated with the Sec proteins, it was concluded that secretion and processing of Pre-Exg took place in the SecYEG translocation machinery. The results were in line with the previous speculation that accumulation of unprocessed precursor proteins in the cytoplasmic membrane was detrimental, and supported the idea that cell death was caused by some unusual tie-up of Pre-Exg with the SecYEG translocation machinery, thus imposing an inhibitory effect on the secretion of endogenous secretory proteins. A new model, designated "Saturated Translocation," was proposed to explain the interchangeable lethal and non-lethal properties of Pre-Exg, and to address the possible scenarios that might occur in the course of cell death triggered by secretion of Pre-Exg.

Cloning, expression, and characterization of diuretic hormone Manduca diuresin from Manduca sexta in Escherichia coli

Manduca diuresin (MD), a 30 amino acid peptide isolated from the tobacco hornworm Manduca sexta, was found to play an important role in the regulation of water and salt balance in the insect. To facilitate studies relating to the function and structure of MD, a synthetic gene encoding MD was assembled and expressed in Escherichia coli. Using an excretion vector, expression of the MD gene in an induced transformant was detected at the transcriptional and translational levels by Northern-blot and ELISA analyses, respectively. With the use of glutathione-S-transferase as the reporter protein, MD was confirmed to be expressed in E. coli. The recombinant product was resolved by reverse-phase HPLC into three peptide groups of different retention times, which were shown by mass spectrometry to be composed of MD deletants missing various lengths of the C-terminus. Despite the deletions and the absence of an amidated C-terminus, the deletants were shown to be biologically active, suggesting the importance of the N-terminus of MD for biological activity.