High-level direct expression of semi-synthetic human interleukin-6 in Escherichia coli and production of N-terminus met-free product

Comparative evaluation of recombinant protein production in different biofactories: the green perspective

In recent years, the production of recombinant pharmaceutical proteins in heterologous systems has increased significantly. Most applications involve complex proteins and glycoproteins that are difficult to produce, thus promoting the development and improvement of a wide range of production platforms. No individual system is optimal for the production of all recombinant proteins, so the diversity of platforms based on plants offers a significant advantage. Here, we discuss the production of four recombinant pharmaceutical proteins using different platforms, highlighting from these examples the unique advantages of plant-based systems over traditional fermenter-based expression platforms.

Treatment with recombinant placental growth factor (PlGF) enhances both angiogenesis and arteriogenesis and improves survival after myocardial infarction

BACKGROUND

Placental growth factor (PlGF), a homolog of vascular endothelial growth factor, is reported to stimulate angiogenesis and arteriogenesis in pathological conditions. It was recently demonstrated that PlGF is rapidly produced in myocardial tissue during acute myocardial infarction (MI). However, the effects of exogenous PlGF administration on the healing process after MI are not fully understood. The purpose of the present study was to examine whether PlGF treatment has therapeutic potential in MI.

METHODS AND RESULTS

Recombinant human PlGF (rhPlGF: 10 microg) was administered continuously for 3 days in a mouse model of acute MI. rhPlGF treatment significantly improved survival rate after MI and preserved cardiac function relative to control mice. The numbers of CD31-positive cells and alpha-smooth muscle actin-positive vessels in the infarct area were significantly increased in the rhPlGF group. Endothelial progenitor cells (Flk-1(+)Sca-1(+) cells) were mobilized by rhPlGF into the peripheral circulation. Furthermore, rhPlGF promoted the recruitment of GFP-labeled bone marrow cells to the infarct area, but only a few of those migrating cells differentiated into endothelial cells.

CONCLUSIONS

Exogenous PlGF plays an important role in healing processes by improving cardiac function and stimulating angiogenesis following MI. It can be considered as a new therapeutic molecule.

Defective immune response and severe skin damage following UVB irradiation in interleukin-6-deficient mice

Interleukin-6 (IL-6), a multifunctional cytokine, is induced in the acute-phase reaction following ultraviolet (UV) irradiation of humans and mice. Using IL-6-deficient (IL-6-/-) mice, we investigated the role of IL-6 in immunosuppression and inflammatory responses caused by UVB (280-320 nm) radiation. The IL-6-/- mice had a defective contact hypersensitivity (CHS) in response to the sensitizers 2,4-dinitrofluorobenzene and oxazolone. The injection of recombinant IL-6 (rIL-6) into these mice resulted in a marked recovery of the CHS. Serum IL-6 was significantly elevated by UV irradiation of wild-type B6 J/129Sv (IL-6+/+) mice but was not detectable in IL-6-/- mice. Interestingly, there was no induction of serum interleukin-10 (IL-10) by UV irradiation of IL-6-/- mice, whereas UV exposure caused a significant increase in serum IL-10 levels in IL-6+/+ mice. Injection of rIL-6 into IL-6-/- mice increased IL-10 to levels similar to those of IL-6+/+ mice. Being different from IL-6+/+ mice, no epidermal proliferation was found at 48 hr in the IL-6-/- mice, but delayed cell proliferation was observed at 72 hr after UV exposure. Immunohistochemical analysis demonstrated that the epidermis was capable of synthesizing IL-6 at 72 hr after UV irradiation of IL-6+/+ mice. In addition, the IL-6-positive cells appeared to be Langerhans' cells, which were detected with dendritic cell-reactive S-100 antibody. The present study strongly suggests that IL-6 may play a crucial role in the alteration of cutaneous immune responses following UV exposure, and provides evidence that IL-6 is a potent inducer of IL-10. Furthermore, IL-6 production induced by UV radiation appears to be an important early signal for repair of UV-caused skin damage.

Genetic characterization of pepP, which encodes an aminopeptidase P whose deficiency does not affect Lactococcus lactis growth in milk, unlike deficiency of the X-prolyl dipeptidyl aminopeptidase

We sequenced the pepP gene of Lactococcus lactis, which encodes an aminopeptidase P (PepP), and demonstrated that the X-prolyl dipeptidyl aminopeptidase PepX plays a more important role than PepP in nitrogen nutrition. PepP shares homology with methionine aminopeptidases and could play a role in the maturation of nascent proteins.

Analysis of recombinant human ADP-ribosylation factors by reversed-phase high-performance liquid chromatography and electrospray mass spectrometry

Two complementary approaches utilizing reverse-phase high-performance liquid chromatography and liquid chromatography/mass spectrometry were developed to analyze recombinantly produced Group I and Group II human ADP-ribosylation factors (ARFs). We observe that the NH2 termini of Group II ARFs (ARF4 and ARF5) are efficiently processed by removal of the initiating methionine. In contrast, the NH2 termini of Group I ARFs (ARF1 and ARF3), although fully deformylated, undergo only partial methionine cleavage. This result is unexpected as ARFs are canonical substrates for methionine processing in both bacterial and eukaryotic systems, but it may explain the difficulties encountered by many researchers attempting to produce myristoylated ARFs in Escherichia coli. Additionally, we observe that a significant fraction of purified ARF4 contains a modification which we demonstrate to be consistent with mono-glutathionation. Both methionine retention and glutathione modification may impact ARF function and the methods presented here should be employed to determine the quality of recombinant ARFs.

Interleukin-6: structure-function relationships

Interleukin-6 (IL-6) is a multifunctional cytokine that plays a central role in host defense due to its wide range of immune and hematopoietic activities and its potent ability to induce the acute phase response. Overexpression of IL-6 has been implicated in the pathology of a number of diseases including multiple myeloma, rheumatoid arthritis, Castleman's disease, psoriasis, and post-menopausal osteoporosis. Hence, selective antagonists of IL-6 action may offer therapeutic benefits. IL-6 is a member of the family of cytokines that includes interleukin-11, leukemia inhibitory factor, oncostatin M, cardiotrophin-1, and ciliary neurotrophic factor. Like the other members of this family, IL-6 induces growth or differentiation via a receptor-system that involves a specific receptor and the use of a shared signaling subunit, gp130. Identification of the regions of IL-6 that are involved in the interactions with the IL-6 receptor, and gp130 is an important first step in the rational manipulation of the effects of this cytokine for therapeutic benefit. In this review, we focus on the sites on IL-6 which interact with its low-affinity specific receptor, the IL-6 receptor, and the high-affinity converter gp130. A tentative model for the IL-6 hexameric receptor ligand complex is presented and discussed with respect to the mechanism of action of the other members of the IL-6 family of cytokines.

Interleukin-6 and granulocyte colony-stimulating factor synergistically increase peripheral blood progenitor cells in myelosuppressive mice

We previously reported a successful peripheral blood stem cell harvest by co-administration of recombinant human (rh) interleukin-6 (IL-6) and rh granulocyte colony-stimulating factor (G-CSF) in normal mice. In the present study, to evaluate further the utility of this observation for autologous peripheral blood stem cell transplantation, we examined the effects of rhIL-6 and rhG-CSF on peripheral blood granulocyte-macrophage colony-forming units (CFU-GM) in carboplatin (CBDCA)-induced and irradiation-induced myelosuppressive mouse models. After CBDCA administration, blood cell counts decreased to the nadir, and then recovered to a normal level. In this recovery phase, the peripheral CFU-GM level increased to 3.8-fold higher than the pretreatment level. Administration of rhIL-6 (10 microgram/day) alone induced a 40-fold increase in peripheral CFU-GM from the normal level at day 14. In combination with rhG-CSF (0.35 microgram/day), which alone induced a 74-fold increase, rhIL-6 synergistically increased the CFU-GM level by 1200-fold. In irradiated mice, similar results were observed. Administration of rhIL-6 at 3 and 10 microgram/day significantly increased CFU-GM. Interestingly, in combination with rhG-CSF, a lower dose of rhIL-6 (1 microg/day) could induce CFU-GM increase. We also examined CFU-GM distribution in bone marrow, spleen and peripheral blood. Cytokine administration induced not only a change of CFU-GM distribution, but also an increase in total CFU-GM counts per mouse. These results suggest that co-administration of rhIL-6 and rhG-CSF may be useful for autologous peripheral blood stem cell transplantation.

High-level expression of a biologically active human interleukin-6 mutein

We have constructed two different muteins of interleukin-6 (IL-6) which were expressed in Escherichia coli. Both muteins lack the first 22 N-terminal amino acids of native IL-6 and lack one or the other of the two naturally occurring pairs of cysteines at either position 45 and 51 or position 74 and 84 of IL-6. We found that there was a dramatic increase in the level of IL-6 produced from each mutein clone, compared to the level produced by the wild-type IL-6 clone. We also observed that the yield of soluble and properly refolded mutein IL-6 was highest when the cysteines at position 74 and 84 were left intact. The mutein IL-6 with cysteines at position 74 and 84 was as active as wild-type IL-6 and a lower concentration of the mutein IL-6 was required to reach maximal activity, compared to wild-type IL-6. The mutein IL-6 with cysteines at position 45 and 51 had a much reduced biological activity.

Renaturation of recombinant proteins produced as inclusion bodies

Expression of recombinant proteins in Escherichia coli often results in the formation of insoluble inclusion bodies. Within the last few years specific methods and strategies have been developed to prepare active proteins from these inclusion bodies. These methods include (i) isolation of inclusion bodies after disintegration of cells by mechanical forces and purification by washing with detergent solutions or low concentrations of denaturant, (ii) solubilization of inclusion bodies with high concentrations of urea or guanidine-hydrochloride in combination with reducing reagents, and (iii) renaturation of the proteins including formation of native disulphide bonds. Renatured and native disulphide bond formation are accomplished by (a) either air oxidation, (b) glutathione reoxidation starting from reduced material, or (c) disulphide interchange starting from mixed disulphides containing peptides. The final yield of renatured proteins can be increased by adding low concentrations of denaturant during renaturation.

Production and secretion of human interleukin 6 into the periplasm of Escherichia coli: efficient processing of N-terminal variants of hIL6 by the E. coli signal peptidase

We have developed a system for expressing human interleukin 6 into the periplasmic space of Escherichia coli. The method is based on the expression of the hIL6 gene under the control of the regulatory signals of plasmid pINIII-OMPA3, i.e., lpp-lac promoter and the E. coli OMPA ribosome binding site and leader sequence. Since microheterogeneity is known to occur in the amino end of the cytokine, we tested different 'natural' versions of the protein, and we found that the secretion process was only efficient when the N-terminal amino acid was not proline. In flask experiments this procedure yields about 8-10 mg of biologically active hIL6 per liter.

Effect of semi-random mutagenesis at the C-terminal 4 amino acids of human interleukin-6 on its biological activity

The carboxyl(C)-terminus of human interleukin-6 (hIL-6) has a critical role in the expression of the biological activity of this cytokine. To define the structure-function relationships of this region, semi-random mutagenesis of the C-terminal Leu181-Arg182-Qln183-Met184 sequence of hIL-6 was performed. The mutants were produced in Escherichia coli, renatured, and purified. Alterations of the C-terminal 4 amino acids caused a significant reduction of the proliferative effect of the mutants on MH60.BSF2 and KT-3 cells, and also led to a drastic decrease in receptor binding affinity. These results suggest the importance of a positively charged residue at position 182 or 183 and an alpha-helix at position 181 for the biological activity of hIL-6.

High-level expression and production of recombinant human interleukin-6 analogs

We have constructed and analyzed different mutant forms of interleukin-6 (IL-6) expressed in Escherichia coli that can be divided into two groups. The first group contains four full-length IL-6 molecules that differ in the presence of cysteine residues involved in disulfide bridges. The second group contains 22 N-terminal amino acid deletions in addition to the differences in the cysteine residues. The different IL-6 muteins were extracted and their expression levels and solubility were compared. We found that the production levels of IL-6 can be dramatically improved by deleting the first 22 N-terminal amino acids of the molecule. We have also found that the production of IL-6 containing the four cysteine residues is lower than the production of the mutant molecules that lack one or both pairs of cysteines. The yield of soluble and properly refolded IL-6 was the highest when the disulfide bond between the cysteines at positions 74 and 84 was present in the mutein form, which also lacked the 22 N-terminal amino acids.

In-vivo processing of the initiator methionine from recombinant methionyl human interleukin-6 synthesized in Escherichia coli overproducing aminopeptidase-P

Human interleukin 6 (hIL-6) overproduced in Escherichia coli HB101 was found to partially retain the initiator methionine (Met) residue (Met-hIL-6). In order to remove the residual N-terminal Met in vivo, an attempt was made to express hIL-6 in aminopeptidase-P (Ap-P)-hyperproducing strains, since the N-terminus Met-Pro- structure of nascent recombinant hIL-6 has been shown to be a favoured substrate of the enzyme in vitro. Using a mutant with duplicated Ap-P genes (pepP) on a chromosome or some recombinant strains overproducing Ap-P, we have succeeded in removing the initiator Met from Met-hIL-6 in vivo. The content of the mature product without the initiator Met in the pepP recombinant strains could be increased to approximately 99% from 85%.

A CHO strain producing high-level human IL-6 with the 3' deletion construct

A Chinese Hamster Ovary (CHO) strain producing high-level human interleukin 6 (IL-6) was obtained, by introduction of the IL-6 cDNA from which the 3' AU-rich region was deleted. The IL-6 mRNA of this strain was stable. The productivity was more than 15 times higher than the previously obtained clone, which has intact IL-6 cDNA in the same expression vector. This strain produced IL-6 at a high level of 30 micrograms ml-1 in batch culture, or a continuous 20 micrograms per 10(6) cells per day in microcarrier cultivation.