Deposition mode of transforming growth factor-β expressed in transgenic rice seed

Improvement of production yield and extraction efficacy of recombinant protein by high endosperm-specific expression along with simultaneous suppression of major seed storage proteins

Human transforming growth factor-β1 (hTGF-β1)　was produced in transgenic rice seeds. To boost its production yield and to extract it simply, it was expressed under the control of seed-specific promoters along with the simultaneous suppression of endogenous seed storage proteins　(SSPs)　through RNA interference (RNAi). When driven by the 26 kDa α-globulin endosperm-specific promoter, it accumulated up to the markedly high level of 452 μg/grain. However, exchange with other seed-specific promoters such as 18 kDa oleosin and AGPase promoters resulted in remarkable reduction to the levels of 62 and 48 μg/grain, respectively, even though endogenous SSPs were reduced to the similar level. These production levels were almost similar to those (42 and 108 μg/grain) produced by the glutelin GluB-1 endosperm-specific promoter and the maize ubiquitin constitutive promoter without reduction of SSPs, respectively. When extracted from these transgenic rice seeds with reduced SSPs with various buffers, it could be solubilized with denaturant solution, which was in remarkable contrast with those without depressed SSPs which required further supplementation of reducing agent for extraction. This difference was associated with the fact that it was mainly deposited to ER-derived structures though self-aggregation or interaction with remaining prolamin via intermolecular disulfide bonds.

Development of Rice-Seed-Based Oral Allergy Vaccines Containing Hypoallergenic Japanese Cedar Pollen Allergen Derivatives for Immunotherapy

Allergen-specific immunotherapy is the only available curative treatment for IgE-mediated allergen diseases. A safe hypoallergenic allergen derivative with high efficiency is required as a tolerogen to induce immune tolerance to the causitive allergens. In this study, to generate a rice-based oral allergy vaccine for Japanese cedar (JC) pollinosis, the tertiary structures of major JC pollen allergens, Cry j 1 and Cry j 2, were more completely destructed by shuffling than the previous ones without losing immunogenicity and then were specifically expressed in the endosperm of transgenic rice seed. They accumulated at high levels and were deposited in endoplasmic reticulum (ER) and ER-derived protein bodies. The low allergenicity of these deconstructed Cry j 1 and Cry j 2 allergens was evaluated by examining their binding activities to the specific IgE antibody and by the basophil degranulation test.

Specific region affects the difference in accumulation levels between apple food allergen Mal d 1 and birch pollen allergen Bet v 1 which are expressed in vegetative tissues of transgenic rice

Specific domain of the Mal d 1 was identified to be mainly involved in higher accumulation level in vegetative tissues of transgenic rice than the Bet v 1. Apple food allergen Mal d 1 and birch pollen allergen Bet v 1 belong to the same pathogen related protein 10 (PR10) family. When green fluorescent protein (GFP) fused to either of these allergens was expressed as a secretory protein in transgenic rice by ligating an N terminal signal peptide and a C terminal KDEL ER retention signal under the control of the maize ubiquitin constitutive promoter, the GFP:Mald1 highly accumulated in various tissues, whereas accumulation level of the GFP:Betv1 was remarkably reduced in vegetative tissues except for seed. Analysis by RT-PCR exhibited that there was little difference in their transcript levels, indicating the involvement of post-transcriptional regulation. To investigate the cause of such difference in accumulation levels, deletion analysis of the Mal d 1 and domain swapping between them were carried out in transgenic rice. The results showed that the region between positions 41-90 in the Mal d 1 is predominantly implicated in higher level accumulation in vegetative tissues as well as seed as compared with the Bet v 1. The GFP:Mald1 was localized in oligomeric form within ER lumen or ER-derived particles in vegetative tissues, whereas in seed mainly deposited into novel huge ER-derived protein bodies with the size of 5-10 µm in aleurone cells.

Compensatory rebalancing of rice prolamins by production of recombinant prolamin/bioactive peptide fusion proteins within ER-derived protein bodies

Bioactive peptide was produced by fusion to rice prolamins in transgenic rice seeds. Their accumulation levels were affected by their deposition sites and by compensatory rebalancing between prolamins within PB-Is. Peptide immunotherapy using analogue peptide ligands (APLs) is one of promising treatments against autoimmune diseases. Use of seed storage protein as a fusion carrier is reasonable strategy for production of such small size bioactive peptides. In this study, to examine the efficacy of various rice prolamins deposited in ER-derived protein bodies (PB-Is), the APL12 from the Glucose-6-phosphate isomerase (GPI325-339) was expressed by fusion to four types of representative prolamins under the control of the individual native promoters. When the 14 and 16 kDa Cys-rich prolamins, which were localized in middle layer of PB-Is, were used for production of the APL12, they highly accumulated in transgenic rice seeds (~ 200 µg/grain). By contrast, fusion to the 10 and 13 kDa prolamins, which were localized in the core and outermost layer of PB-Is, resulted in lower levels of accumulation (~ 40 µg/grain). These results suggest that accumulation levels were highly affected by their deposition sites. Next, when different prolamin/APL12 fusion proteins were co-expressed to increase accumulation levels, they could not be increased so much as their expected additive levels. High accumulation of one type prolamin/APL12 led to reduction of other type(s) prolamin/APL12 to maintain the limited amounts of prolamins that can be deposited in PB-Is. Moreover, suppression of endogenous seed proteins by RNA interference also did not significantly enhance the accumulation levels of prolamin/APL12. These findings suggest that there may be compensatory rebalancing mechanism that controls the accumulation levels of prolamins deposited within PB-Is.

Protection of Human Colon Cells from Shiga Toxin by Plant-based Recombinant Secretory IgA

Shiga toxin is a major virulence factor of food-poisoning caused by Escherichia coli such as O157:H7. Secretory immunoglobulin (Ig) A (SIgA) is supposed to prevent infection of the mucosal surface and is a candidate agent for oral immunotherapy. We previously established a recombinant monoclonal antibody (mAb) consisting of variable regions from a mouse IgG mAb specific for the binding subunit of Shiga toxin 1 (Stx1) and the Fc region of mouse IgA. Here we produced a secretory form of the recombinant IgA (S-hyIgA) with transgenic Arabidopsis thaliana plant. All the S-hyIgA cDNAs (heavy, light, J chain and secretory component) were expressed under the control of a bidirectional promoter of a chlorophyll a/b-binding protein of A. thaliana without using a viral promoter. The plant-based S-hyIgA exhibited antigen binding, and was modified with plant-specific N-linked sugar chains. The Ig heavy chain and secretory components were observed in an intracellular protein body-like structure of the transgenic leaves on immuno-electron microscopy. An extract of the transgenic leaves neutralized the cytotoxicity of Stx1 toward butyrate-treated Caco-2 cells, a human colon carcinoma cell line. These results will contribute to the development of edible therapeutic antibodies such as those for the treatment of mucosal infection.