Expression of The Human Acidic Fibroblast Growth Factor in Transgenic Tomato and Safety Assessment of Transgenic Lines

Efficient Soluble Expression and Purification of Recombinant Human Acidic Fibroblast Growth Factor from Escherichia coli via Fusion with a Novel Collagen-like Protein Scl2

Human acidic fibroblast growth factor (haFGF) is a multifunctional protein involved in regulating a wide range of cellular processes. As a potent therapeutic agent, it is highly desirable to produce recombinant haFGF (r-haFGF) at low cost. However, the complex structure and formation of aggregation confines its high-level soluble expression and functional form. Herein, to produce r-haFGF efficiently in E. coli, we devised a novel soluble expression and cost-effective purification approach based on fusion with Scl2-M (a novel modified collagen-like protein) for the first time. By using this strategy, more than 95% of the Scl2-M-haFGF fusion protein was highly expressed in soluble form and the expression level of targeted fusion protein in shake flasks and 5-L fermenter was 0.42 g/L and 2.28 g/L, respectively. Subsequently, the recombinant Scl2-M-haFGF was readily purified through a facile process of acid precipitation and subjected to enterokinase (EK) cleavage. After Scl2-M cleavage, tag-free r-haFGF was further purified using ion-exchange chromatography. The recovery rate of the whole purification process attained 34.2%. Furthermore, the resulting high-purity (96.0%) r-haFGF was prepared by freeze-drying as a final product, and its bioactivity was confirmed to potentiate the proliferation of L929 and BALB-3T3 fibroblasts. Overall, our developed method has the potential for the massive production of the r-haFGF in the future.

Identification of sugar response complex in the metallothionein OsMT2b gene promoter for enhancement of foreign protein production in transgenic rice

A 146-bp sugar response complex MTSRC is identified in the promoter of rice metallothionein OsMT2b gene conferring high-level expression of luciferase reporter gene and bioactive recombinant haFGF in transgenic rice. A rice subfamily type 2 plant metallothionein (pMT) gene, OsMT2b, encoding a reactive oxygen species (ROS) scavenger protein, has been previously shown to exhibit the most abundant gene expression in young rice seedling. Expression of OsMT2b was found to be regulated negatively by ethylene and hydrogen peroxide in rice stem node under flooding stress, but little is known about its response to sugar depletion. In this study, transient expression assay and transgenic approach were employed to characterize the regulation of the OsMT2b gene expression in rice. We found that the expression of OsMT2b gene is induced by sugar starvation in both rice suspension cells and germinated embryos. Deletion analysis and functional assay of the OsMT2b promoter revealed that the 5'-flanking region of the OsMT2b between nucleotides - 351 and - 121, which contains the sugar response complex (- 266 to - 121, designated MTSRC) is responsible for high-level promoter activity under sugar starvation. It was also found that MTSRC significantly enhances the Act1 promoter activity in transgenic rice cells and seedlings. The modified Act1 promoter, Act1-MTSRC, was used to produce the recombinant human acidic fibroblast growth factor (haFGF) in rice cells. Our result shows that the bioactive recombinant haFGF is stably produced in transformed rice cell culture and yields are up to 2% of total medium proteins. Our studies reveal that MTSRC serves as a strong transcriptional activator and the Act1-MTSRC promoter can be applicable in establishing an efficient expression system for the high-level production of foreign proteins in transgenic rice cells and seedlings.