Preparation of bioactive soluble human leukemia inhibitory factor from recombinant Escherichia coli using thioredoxin as fusion partner

Production of biologically active recombinant buffalo leukemia inhibitory factor (BuLIF) in Escherichia Coli

Background

Leukemia inhibitory factor (LIF) is a multifunctional cytokine which plays multiple roles in different biological processes such as implantation, bone remodeling, and hematopoiesis. The buESCs are difficult to culture due to lack of proper understanding of the culture conditions. LIF is one of the important factors which maintain the pluripotency in embryonic stem cells and commercial LIF from murine and human origin is used in the establishment of buffalo embryonic stem cells (buESCs). The LIF from a foreign origin is not able to maintain pluripotency and proliferation in buESCs for a long term which is contributed by difference in the binding sites on LIF; therefore, culture medium supplemented with buffalo-specific LIF may enhance the efficiency of buESCs by improving the environment of culture conditions. The high cost of LIF is another major drawback which restricts buESCs research, thus limits the scope of buffalo stem cell use. Various methods have been developed to produce human and murine LIF in prokaryotic system. However, Buffalo leukemia inhibitory factor (BuLIF) has not been yet produced in prokaryotic system. Here, we describe a simple strategy for the expression and purification of biologically active BuLIF in Escherichia coli (E. coli).

Results

The BuLIF cDNA from buffalo (Bubalus bubalis) was cloned into pET22b(+) and expressed in E. coli Lemo-21(DE3). The expression of BuLIF was directed into periplasmic space of E. coli which resulted in the formation of soluble recombinant protein. One step immobilized metal affinity chromatography (IMAC chromatography) was performed for purification of BuLIF with ≥ 95% of homogeneity. The recombinant protein was confirmed by western blot and identified by mass spectroscopy. The biological activity of recombinant BuLIF was determined on murine myeloid leukemic cells (M1 cells) by MTT proliferation assay. The addition of BuLIF increased the reduction of MTT by stimulated M1 cells in a dose-dependent manner. The BuLIF induced the formation of macrophage like structures from M1 cells where they engulfed fluorescent latex beads. The recombinant BuLIF successfully maintained pluripotency in buffalo embryonic stem cells (buESCs) and were positive for stem cells markers such as Oct-4, Sox-2, Nanog, and alkaline phosphatase activity.

Conclusions

The present study demonstrated a simple method for the production of bioactive BuLIF in E. coli through single step purification. BuLIF effectively maintained buffalo embryonic stem cells pluripotency. Thus, this purified BuLIF can be used in stem cell study, biomedical, and agricultural research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00328-1.

Distinct contributions of DNA methylation and histone acetylation to the genomic occupancy of transcription factors

Epigenetic modifications on chromatin play important roles in regulating gene expression. Although chromatin states are often governed by multilayered structure, how individual pathways contribute to gene expression remains poorly understood. For example, DNA methylation is known to regulate transcription factor binding but also to recruit methyl-CpG binding proteins that affect chromatin structure through the activity of histone deacetylase complexes (HDACs). Both of these mechanisms can potentially affect gene expression, but the importance of each, and whether these activities are integrated to achieve appropriate gene regulation, remains largely unknown. To address this important question, we measured gene expression, chromatin accessibility, and transcription factor occupancy in wild-type or DNA methylation-deficient mouse embryonic stem cells following HDAC inhibition. We observe widespread increases in chromatin accessibility at retrotransposons when HDACs are inhibited, and this is magnified when cells also lack DNA methylation. A subset of these elements has elevated binding of the YY1 and GABPA transcription factors and increased expression. The pronounced additive effect of HDAC inhibition in DNA methylation-deficient cells demonstrates that DNA methylation and histone deacetylation act largely independently to suppress transcription factor binding and gene expression.

Efficient production process of bioactive recombinant human leukemia inhibitory factor in Chinese hamster ovary cells

The rhLIF is widely used as an essential factor in stem cell cultures for cell therapies. However, all the recombinant LIFs commercially available are expensive, and no commercially available rhLIF meet the standards recommended by USP for use in cell therapies. The current study reports the efficient production of N-glycosylated and bioactive rhLIF in CHO cells. The production rate of established rhLIF-expressing rCHO cells was approximately 0.85 g/l in 12-day fed-batch cultures using a 7.5 l bioreactor. The rhLIF protein was purified via a four-step purification procedure with approximately 57% recovery rate and greater than 99% purity. The purified rhLIF was N-glycosylated and biologically active with an EC₅₀ of 0.167 ng/ml and a specific activity of 0.86 × 10³ IU/mg. The purification procedure controlled the levels of process-related impurities below critical levels recommended by USP for cytokines used in cell therapies. The current work is the first production process of N-glycosylated and bioactive rhLIF, which can be applied to large-scale manufacture of GMP-grade rhLIF for use as an ancillary material in cell therapy.

Production and characterization of recombinant human leukemia inhibitory factor and evaluation of anti-fertility effects of rabbit anti-rhLIF in Balb/c mice

Human leukemia inhibitory factor (hLIF) is a cytokine of interleukin-6 family. This study aimed to evaluate the recombinant production rate of active hLIF by different vector-host systems under various conditions. Moreover, a rabbit polyclonal antibody (pAb) against recombinant hLIF (rhLIF) was produced and its anti-fertility effects were explored in Balb/c mice. Four different constructs including pET22b/hLIF, pET28b/hLIF, pET32b/hLIF and pColdI/hLIF were designed and transformed into BL21-(DE3), Rosetta-(DE3), Origami-(DE3) and Shuffle T7-(DE3) host cells. The expression level and proliferative effect of rhLIF were measured by SDS-PAGE and MTT assays, respectively. Rabbit pAb to rhLIF was produced and characterized using enzyme-linked immunosorbent assay and western blot techniques. The Balb/c mice were divided into two intervention and control groups. Then, they were intraperitoneally injected by purified rabbit anti-rhLIF and non-immunized rabbit pAb, respectively. After sacrifice on day 7, the number of implantation sites was counted. The rhLIF was successfully expressed by pET32b/hLIF and pColdI/hLIF vectors in all hosts with no significant difference in the rate of their expression. The rhLIF was purified and checked for activity. The results showed that it is functionally active and the produced anti-rhLIF pAb could specifically bind to commercial rhLIF. Passive immunization results showed that anti-rhLIF antibody completely inhibited fertility in all injected Balb/c mice compared to controls. Although previous studies showed expression of rhLIF using various methods, using different vector-host systems ensures us of successful biological active expression of it. The pAb against rhLIF could be a powerful tool for inducing in vivo infertility.

Soluble expression, rapid purification, biological identification of chicken interferon-alpha using a thioredoxin fusion system in E. coli and its antiviral effects to H9N2 avian influenza virus

In this paper, we report a soluble expression based on Escherichia coli and two-step purification of a novel thioredoxin-tagged chicken interferon-α fusion protein (Trx-rChIFN-α) by using pET32a(+) expression system. The mature ChIFN-α gene was amplified by Reverse transcriptase-polymerase chain reaction (RT-PCR) and subcloned into pET-32a (+) vector prior to transformation into Rosetta (DE3) competent cells. After IPTG induction, the recombinant fusion protein was expressed efficiently in the soluble fraction. The protein purification was performed by nickel affinity chromatography and DEAE anion exchange chromatography. The purified product has a purity of 95% with a yield of 47.3 mg/L of culture. The specific activity of the fusion protein reaches to 2.0 × 10⁷ IU/mg as determined in the CEF/VSV titration system. After excision of the Trx tag by enterokinase, the remaining solo protein was confirmed as rChIFN-α protein by SDS-PAGE, N-terminal sequencing and mass spectrometry. The effects of this Trx-rChIFN-α fusion protein against H9N2 influenza virus infection were also evaluated in ovo. The results showed that the Trx-rChIFN-α protein could significantly reduce the hemagglutination titer of H9N2 virus, and the H9N2 viruses HA gene copy numbers. These findings will enable us to produce large amount and bio-active rChIFN-α protein for future applications.

Expression, Purification, and Characterization of a Novel Hybrid Peptide with Potent Antibacterial Activity

The hybrid peptide cecropin A (1⁻8)⁻LL37 (17⁻30) (C⁻L), derived from the sequence of cecropin A (C) and LL-37 (L), showed significantly increased antibacterial activity and minimized hemolytic activity than C and L alone. To obtain high-level production of C⁻L, the deoxyribonucleic acid sequence encoding C⁻L with preferred codons was cloned into pET-SUMO to construct a fusion expression vector, and overexpressed in Escherichia coli (E. coli) BL21 (DE3). The maximum fusion protein (92% purity) was obtained with the yield of 89.14 mg/L fermentation culture after purification with Ni-NTA Sepharose column. The hybrid C⁻L was cleaved from the fusion protein by SUMO-protease, and 17.54 mg/L pure active C⁻L was obtained. Furthermore, the purified C⁻L showed identical antibacterial and hemolytic activity to synthesized C⁻L. Stability analysis results exhibited that the activity of C⁻L changed little below 80 °C for 20 min, but when the temperature exceeded 80 °C, a significant decrease was observed. Varying the pH from 5.0 to 10.0 did not appear to influence the activity of C⁻L, however, pH below 4.0 decreased the antibacterial activity of C⁻L rapidly. Under the challenge of several proteases (pepsin, trypsin, and proteinase K), the functional activity of C⁻L was maintained over 50%. In summary, this study not only supplied an effective approach for high-level production of hybrid peptide C⁻L, but paved the way for its further exploration in controlling infectious diseases of farm animals or even humans.

Production of soluble bioactive mouse leukemia inhibitory factor from Escherichia coli using MBP tag

Embryonic stem cells and induced pluripotent stem cells depend on one of cytokines called leukemia inhibitory factor (LIF) to retain their undifferentiated state and pluripotency. Nevertheless, further progresses of stem cell scientific investigation and its possible application are limited owing to the expense of commercial LIF. Here we introduced a simple, practical and high level expression of MBP-mouse LIF through Escherichia coli system which was bioactive. The mLIF cDNA was inserted into vector of pMAL-C2X in order to generate N-terminal MBP-mLIF recombinant proteins in the cytoplasm of Escherichia coli. MBP-mLIF as a soluble form was expressed. One-step purification through gravitational affinity chromatography was accomplished to acquire high purity (>92%) MBP-mLIF. The MBP-mLIF products specifically suppressed the growth of M1cells in a dose-dependent pattern. MBP-mLIF also was proved the ability to maintain the pluripotency of iPSCs. These outcomes revealed that the N-end MBP tags of the MBP-mLIF did not obstruct mLIF bioactivity. This method to generate recombinant MBP-mLIF is a simple, practical, economical and user-friendly protocol.

Online analysis of protein inclusion bodies produced in E. coli by monitoring alterations in scattered and reflected light

The online monitoring of recombinant protein aggregate inclusion bodies during microbial cultivation is an immense challenge. Measurement of scattered and reflected light offers a versatile and non-invasive measurement technique. Therefore, we investigated two methods to detect the formation of inclusion bodies and monitor their production: (1) online 180° scattered light measurement (λ = 625 nm) using a sensor platform during cultivation in shake flask and (2) online measurement of the light reflective interference using a porous Si-based optical biosensor (SiPA). It could be shown that 180° scattered light measurement allows monitoring of alterations in the optical properties of Escherichia coli BL21 cells, associated with the formation of inclusion bodies during cultivation. A reproducible linear correlation between the inclusion body concentration of the non-fluorescent protein human leukemia inhibitory factor (hLIF) carrying a thioredoxin tag and the shift ("Δamp") in scattered light signal intensity was observed. This was also observed for the glutathione-S-transferase-tagged green fluorescent protein (GFP-GST). Continuous online monitoring of reflective interference spectra reveals a significant increase in the bacterium refractive index during hLIF production in comparison to a non-induced reference that coincide with the formation of inclusion bodies. These online monitoring techniques could be applied for fast and cost-effective screening of different protein expression systems.

Smart sustainable bottle (SSB) system for E. coli based recombinant protein production

Background

Recombinant proteins are usually required in laboratories interested in the protein but not in the production process itself. Thus, technical equipment which is easy to handle and straight forward protein production procedures are of great benefit to those laboratories. Companies selling single use cultivation bags and bioreactors are trying to satisfy at least part of these needs. However, single-use systems can contribute to major costs which might be acceptable when “good manufacturing practices” are required but not acceptable for most laboratories facing tight funding.

Results

The assembly and application of a simple self-made “smart sustainable bottle” (SSB) system for E. coli based protein production is presented. The core of the SSB system is a 2-L glass bottle which is operated at constant temperature, air flow, and stirrer speed without measurement and control of pH and dissolved oxygen. Oxygen transfer capacities are in the range as in conventional bioreactors operated at intermediate aeration rates and by far exceed those found in conventional shaking flasks and disposable bioreactors. The SSB system was applied for the production of various recombinant proteins using T7-based expression systems and a defined autoinduction medium. The production performance regarding amount and solubility of proteins with robust and delicate properties was as good as in state-of-the-art stirred tank commercial bioreactors.

Conclusions

The SSB system represents a low cost protein production device applicable for easy, effective, and reproducible recombinant protein production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-014-0153-9) contains supplementary material, which is available to authorized users.

Modified lentiviral LTRs allow Flp recombinase-mediated cassette exchange and in vivo tracing of "factor-free" induced pluripotent stem cells

Methods for generating induced pluripotent stem cells (iPSCs) for disease modeling and cell therapies have progressed from integrating vectors to transient delivery of reprogramming factors, avoiding permanent genomic modification. A major limitation of unmodified iPSCs is the assessment of their distribution and contribution to adverse reactions in autologous cell therapy. Here, we report that polycistronic lentiviral vectors with single Flp recombinase (Flp) recognition target (FRT) sites can be used to generate murine iPSCs that are devoid of the reprogramming cassette but carry an intergenic 300-bp long terminal repeat sequence. Performing quantitative polymerase chain reaction on this marker, we could determine genetic identity and tissue contribution of iPSC-derived teratomas in mice. Moreover, we generated iPSCs carrying heterospecific FRT twin sites, enabling excision and recombinase-mediated cassette exchange (RMCE) of the reprogramming cassette for another expression unit of choice. Following screening of iPSCs for "safe harbor" integration sites, expression cassettes were introduced by RMCE into various previously silenced loci of selected single-copy iPSCs. Analysis of DNA methylation showed that RMCE reverted the local epigenetic signature, which allowed transgene expression in undifferentiated iPSCs and in differentiated progeny. These findings support the concept of creating clonotypically defined exchangeable and traceable pluripotent stem cells for disease research and cell therapy.

Soluble expression of human leukemia inhibitory factor with protein disulfide isomerase in Escherichia coli and its simple purification

Human leukemia inhibitory factor (hLIF) is a multifunctional cytokine that is essential for maintaining the pluripotency of embryonic stem cells. hLIF may be also be useful in aiding fertility through its effects on increasing the implantation rate of fertilized eggs. Thus these applications in biomedical research and clinical medicine create a high demand for bioactive hLIF. However, production of active hLIF is problematic since eukaryotic cells demonstrate limited expression and prokaryotic cells produce insoluble protein. Here, we have adopted a hybrid protein disulfide isomerase design to increase the solubility of hLIF in Escherichia coli. Low temperature expression of hLIF fused to the b'a' domain of protein disulfide isomerase (PDIb'a') increased the soluble expression in comparison to controls. A simple purification protocol for bioactive hLIF was established that includes removal of the PDIb'a' domain by cleavage by TEV protease. The resulting hLIF, which contains one extra glycine residue at the N-terminus, was highly pure and demonstrated endotoxin levels below 0.05 EU/μg. The presence of an intramolecular disulfide bond was identified using mass spectroscopy. This purified hLIF effectively maintained the pluripotency of a murine embryonic stem cell line. Thus we have developed an effective method to produce a pure bioactive version of hLIF in E. coli for use in biomedical research.