Expression, Purification, and Polyethylene Glycol Site-Specific Modification of Recombinant Human Interleukin 24 in Escherichia coli

Adaptation process of engineered cell line FCHO/IL-24 stably secreted rhIL-24 in serum-free suspension culture

Interleukin-24 (IL-24) displays tumor cell-specific proliferation inhibition in vitro and in vivo. Recombinant human IL-24 (rhIL-24) has significantly higher activity, yet significantly lower expression level in mammalian cells than in bacteria. To further realize therapeutic potential of IL-24, we enhanced rhIL-24 expression in mammalian cell systems by adapting engineered Flp-In^TMCHO/IL-24 (FCHO/IL-24) cells (adherent cultured in Ham's F12 medium with 10% serum) to serum-free suspension culture. First, MTT assay showed that among four different media (F12, DMEM/F12, 1640 and DMEM), DMEM/F12 medium was the most suitable media for lower-serum adherent culture. Then, cells were adherently cultured in DMEM/F12 with serum concentration reduced from 10% to 0.5% in a gradient manner. Compared to cells in 10% serum, cells in 0.5% serum displayed significantly lower relative cell viability by 40%, increased G0/G1 phase arrest (8.5 ± 2.4%, p < 0.05), decreased supernatant rhIL-24 concentration by 73%, and altered metabolite profiles, such as glucose, lactate and ammonia concentration. Next, the cells were directly adapted to 0.5% serum suspension culture in 125 mL shake flask at 119 rpm with the optimal cell seeding density of 5 × 10⁵ cells/mL (3.3 times higher than that of adherent culture), under which the concentration of rhIL-24 in culture medium was stable at 3.5 ng/mL. Finally, cells adapted to 0.5% serum proliferated better in serum-free medium Eden™-B300S with higher rhIL-24 expression level compared to CDM4CHO. The successful adaptation of engineered cells FCHO/IL-24 laid foundation for adapting cells from adherent culture to suspension serum-free culture to mass produce rhIL-24 protein for therapeutic purposes.

Enhancement of recombinant human IL-24 (rhIL-24) protein production from site-specific integrated engineered CHO cells by sodium butyrate treatment

Interleukin-24 (IL-24) has specific inhibitory effects on the proliferation of various tumor cells with almost no toxicity to normal cells. The antitumor activity of recombinant human IL-24 protein produced in mammalian cells is much higher than that of bacteria, but its expression level is extremely low. Sodium butyrate (NaBu) was utilized as a media additive to increase protein expression in Chinese hamster ovary cells. The site-specific integrated engineered cells FCHO/IL-24 were treated with NaBu under different culture conditions (10% and 0.5% serum adherent culture, 0.5% serum suspension culture). First, 3 days of 1 mmol/L NaBu treatment significantly increased rhIL-24 expression level in FCHO/IL-24 cells by 119.94 ± 1.5% (**p < 0.01), 57.49 ± 2.4% (**p < 0.01), and 20.17 ± 3.03% (*p < 0.05) under the above culture conditions. Second, NaBu has a time- and dose-dependent inhibitory effect on FCHO/IL-24 proliferation and induces G0/G1 phase arrest. Under 10% and 0.5% serum adherent culture, G0/G1 phase cells were increased by 11.3 ± 0.5% (**p < 0.01) and 15.0 ± 2.6% (**p < 0.01), respectively. No induction of apoptosis was observed under a high dosage of NaBu treatment. These results suggest that NaBu increases rhIL-24 secretion via inhibiting cell cycle progression, thereby trapping cells in the highly productive G0/G1 phase. Finally, with increasing NaBu dose, glucose concentration increased (**p < 0.01) while lactic acid and ammonia concentrations reduced significantly (**p < 0.01) in 10% and 0.5% serum adherent culture supernatant. RNA-seq showed that NaBu treatment affected multiple tumor and immune-related pathways. In conclusion, NaBu treatment dramatically promoted rhIL-24 production in engineered FCHO/IL-24 cells by altering downstream pathways and inducing G0/G1 cell arrest with little effect on apoptosis.

Protein Production and Purification of a Codon-Optimized Human NGN3 Transcription Factor from E. coli

Neurogenin 3 (NGN3) transcription factor is vital for the development of endocrine cells of the intestine and pancreas. NGN3 is also critical for the neural precursor cell determination in the neuroectoderm. Additionally, it is one of the vital transcription factors for deriving human β-cells from specialized somatic cells. In the current study, the production and purification of the human NGN3 protein from Escherichia coli (E. coli) is reported. First, the 642 bp protein-coding nucleotide sequence of the NGN3 gene was codon-optimized to enable enhanced protein expression in E. coli strain BL21(DE3). The codon-optimized NGN3 sequence was fused in-frame to three different fusion tags to enable cell penetration, nuclear translocation, and affinity purification. The gene insert with the fusion tags was subsequently cloned into an expression vector (pET28a( +)) for heterologous expression in BL21(DE3) cells. A suitable genetic construct and the ideal expression conditions were subsequently identified that produced a soluble form of the recombinant NGN3 fusion protein. This NGN3 fusion protein was purified to homogeneity (purity > 90%) under native conditions, and its secondary structure was retained post-purification. This purified protein, when applied to human cells, did not induce cytotoxicity. Further, the cellular uptake and nuclear translocation of the NGN3 fusion protein was demonstrated followed by its biological activity in PANC-1 cells. Prospectively, this recombinant protein can be utilized for various biological applications to investigate its functionality in cell reprogramming, biological processes, and diseases.