Temporal and spatial distribution of erythropoietin in transgenic tobacco plants

High yield secretion of human erythropoietin from tobacco cells for ex vivo differentiation of hematopoietic stem cells towards red blood cells

Human erythropoietin (EPO) is a key cytokine in erythropoiesis by regulating differentiation of erythroid progenitor cells into red blood cells (RBCs). Plant cell cultures are considered as promising alternative bioproduction platforms for EPO. To overcome the bottlenecks of low protein productivity and secretion, EPO was expressed in tobacco BY-2 cells with a designer peptide tag, termed (SP)20 that consists of 20 tandem repeats of a "Ser-Pro" motif. This de novo designed tag directed extensive O-glycosylation on each Pro residue in plant cells and acted as a molecular carrier to promote the extracellular secretion of EPO. To facilitate the establishment of stable and high-expression BY-2 cell lines, EPO molecules were co-expressed with a reporter protein GFP, which could be used as a visual marker to monitor the protein expression during the subculture. The engineered (SP)20 glycomodule substantially increased the secreted yields of EPO up to 4.31 μg/mL. The (SP)20-tagged EPOs exhibited the expected activity in promoting the proliferation of TF-1 cells, though their EC50 was 12-fold higher than that of EPO standard. The (SP)20-tagged EPOs could also stimulate the ex vivo expansion and differentiation of hematopoietic stem cell (CD34+ cells) towards RBCs.

Biologically active recombinant human erythropoietin expressed in hairy root cultures and regenerated plantlets of Nicotiana tabacum L

Hairy root culture is a potential alternative to conventional mammalian cell culture to produce recombinant proteins due to its ease in protein recovery, low costs and absence of potentially human pathogenic contaminants. The current study focussed to develop a new platform of a hairy root culture system from Nicotiana tabacum for the production of recombinant human EPO (rhEPO), which is regularly produced in mammalian cells. The human EPO construct was amplified with C-terminal hexahistidine tag from a cDNA of Caco-2 cells. Two versions of rhEPO clones, with or without the N-terminal calreticulin (cal) fusion sequence, were produced by cloning the amplified construct into gateway binary vector pK7WG2D. Following Agrobacterium rhizogenes mediated transformation of tobacco explants; integration and expression of constructs in hairy roots were confirmed by several tests at DNA, RNA and protein levels. The amount of intracellular rhEPO from hairy root cultures with cal signal peptide was measured up to 66.75 ng g-1 of total soluble protein. The presence of the ER signal peptide (cal) was essential for the secretion of rhEPO into the spent medium; no protein was detected from hairy root cultures without ER signal peptide. The addition of polyvinylpyrrolidone enhanced the stabilization of secreted rhEPO leading to a 5.6 fold increase to a maximum concentration of 185.48 pg rhEPOHR g-1 FW hairy root cultures. The rhizo-secreted rhEPO was separated by HPLC and its biological activity was confirmed by testing distinct parameters for proliferation and survival in retinal pigment epithelial cells (ARPE). In addition, the rhEPO was detected to an amount 14.8 ng g-1 of total soluble leaf protein in transgenic T0 generation plantlets regenerated from hairy root cultures with cal signal peptide.

Expression and large-scale production of human tissue plasminogen activator (t-PA) in transgenic tobacco plants using different signal peptides

An attempt was made to assess the expression level and targeting of a human protein entitled recombinant tissue plasminogen activator (rt-PA) through accumulation in three cellular compartments including the endoplasmic reticulum and cytosolic and apoplastic spaces in transgenic tobacco plants. In this context, three chimeric constructs pBI-SP-tPA, pBI-tPA-KDEL, and pBI-Ext-tPA were employed and transferred into the tobacco plants through a popular transformation-based system called Agrobacterium tumefaciens. As an initial screening system, the incorporation of the rt-PA gene in the genomic DNA of tobacco transgenic plants and the possible existence of the rt-PA-specific transcript in the total RNAs of transgenic plant leaves were confirmed via PCR and reverse transcription (RT)-PCR, respectively. Southern blot analysis, in addition, was used to determine the copy number of the corresponding gene (i.e., t-PA) transformed into the each transgenic plant; one or more copies were detected regarding transformants derived from all three abovementioned constructs. According to the enzyme-linked immunosorbent assay, the mean values of t-PA expression were calculated as 0.50, 0.68, and 0.69 μg/mg of the total soluble protein when a collection containing 30 transgenic plants transformed with pBI-SP-tPA, pBI-tPA-KDEL, and pBI-Ext-tPA was taken into account, respectively. The zymography assay was lastly performed and concluded the expression of the properly folded rt-PA in this expression system. Our results, altogether, revealed that tobacco plants could be utilized as a bioreactor system for the large-scale production of enzymatically active t-PA and presumably other therapeutic recombinant proteins in large quantities.

Tobacco as biofactory for biologically active hPL production: a human hormone with potential applications in type-1 diabetes

Human placental lactogen (hPL) is a peptidic hormone that belongs to the short list of growth factors that could treat type-1 diabetes through pancreatic islet transplantation. Placental lactogen has the capacity to improve islet survival and function before or after transplantation. In this study, transgenic tobacco plants were used as a novel expression system for the production of recombinant hPL protein (rhPL). The expression vector pNEKhPL2 containing hPL cDNA was introduced into tobacco plants; the transcriptional activity was confirmed by real-time PCR, and the rhPL levels reached 1% of the total soluble protein (TSP) content in plants cultivated in the greenhouse. In vitro bioassays using the rat insulinoma (INS-1) cell line showed that recombinant protein was able to induce cell proliferation and activate the JAK-2/STAT-5 signal transduction pathway, demonstrating that plant cells can produce the biologically active hPL protein. To further characterize the plant expression system for hPL production, we analyzed the stability of the protein during the life cycle of tobacco plants as well as the transmission of the transgenic trait to the progeny. The recombinant protein was stably accumulated in young leaves, reaching the maximum level in the first month (6.51 μg/g of fresh weight), but showing a decreasing trend of 26% from the initial sampling time until the end of plant's life cycle. The progeny of the selected pNEKhPL2 plant showed in vitro expression levels of up to 1.1% of TSP. Our results therefore indicate that transgenic plants are a suitable expression system for hPL production.

Recombinant protein production in a variety of Nicotiana hosts: a comparative analysis

Although many different crop species have been used to produce a wide range of vaccines, antibodies, biopharmaceuticals and industrial enzymes, tobacco has the most established history for the production of recombinant proteins. To further improve the heterologous protein yield of tobacco platforms, transient and stable expression of four recombinant proteins (i.e. human erythropoietin and interleukin-10, an antibody against Pseudomonas aeruginosa, and a hyperthermostable α-amylase) was evaluated in numerous species and cultivars of Nicotiana. Whereas the transient level of recombinant protein accumulation varied significantly amongst the different Nicotiana plant hosts, the variety of Nicotiana had little practical impact on the recombinant protein concentration in stable transgenic plants. In addition, this study examined the growth rate, amount of leaf biomass, total soluble protein levels and the alkaloid content of the various Nicotiana varieties to establish the best plant platform for commercial production of recombinant proteins. Of the 52 Nicotiana varieties evaluated, Nicotiana tabacum (cv. I 64) produced the highest transient concentrations of recombinant proteins, in addition to producing a large amount of biomass and a relatively low quantity of alkaloids, probably making it the most effective plant host for recombinant protein production.