ER stress response induced by the production of human IL-7 in rice endosperm cells.
Rice seed has been used as a production platform for high value recombinant proteins. When mature human interleukin 7 (hIL-7) was expressed as a secretory protein in rice endosperm by ligating the N terminal glutelin signal peptide and the C terminal KDEL endoplasmic reticulum (ER) retention signal to the hIL-7 cytokine to improve production yield, this protein accumulated at levels visible by Coomassie Brilliant Blue staining. However, the production of this protein led not only to a severe reduction of endogenous seed storage proteins but also to a deterioration in grain quality. The appearance of aberrant grain phenotypes (such as floury and shrunken) was attributed to ER stress induced by the retention of highly aggregated unfolded hIL-7 in the ER lumen, and the expression levels of chaperones such as BiPs and PDIs were enhanced in parallel with the increase in hIL-7 levels. The activation of this ER stress response was shown to be mainly mediated by the OsIRE1-OsbZIP50 signal cascade, based on the appearance of unconventional splicing of OsbZIP50 mRNA and the induction of OsBiP4&5. Interestingly, the ER stress response could be induced by lower concentrations of hIL-7 versus other types of cytokines such as IL-1b, IL-4, IL-10, and IL-18. Furthermore, several ubiquitin 26S proteasome-related genes implicated in ER-associated degradation were upregulated by hIL-7 production. These results suggest that severe detrimental effects on grain properties were caused by proteo-toxicity induced by unfolded hIL-7 aggregates in the ER, resulting in the triggering of ER stress.
Functional Transgenic Crops Research Unit, Genetically Modified Organism Research Center, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602, Japan.
Kyoko
K
Kudo
Masaru
M
Ohta
Lijun
L
Yang
Yuhya
Y
Wakasa
Sakiko
S
Takahashi
Fumio
F
Takaiwa
D000818:Animals; D059865:Endoplasmic Reticulum Stress / Q000235:genetics; D060746:Endoplasmic Reticulum-Associated Degradation / Q000235:genetics; D056625:Endosperm / Q000166:cytology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006031:Glycosylation; D006801:Humans; D015851:Interleukin-7 / Q000096:biosynthesis*; D042541:Intracellular Space / Q000378:metabolism; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism; D012275:Oryza / Q000166:cytology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D020836:Protein Structure, Quaternary; D021381:Protein Transport; D020133:Reverse Transcriptase Polymerase Chain Reaction
C508605:IL7 protein, human; D015851:Interleukin-7; D018832:Molecular Chaperones; D010940:Plant Proteins