Overexpression of a gene that encodes the first enzyme in the biosynthesis of asparagine-linked glycans makes plants resistant to tunicamycin and obviates the tunicamycin-induced unfolded protein response.
The cytotoxic drug tunicamycin kills cells because it is a specific inhibitor of UDP-N-acetylglucosamine:dolichol phosphate N-acetylglucosamine-1-P transferase (GPT), an enzyme that catalyzes the initial step of the biosynthesis of dolichol-linked oligosaccharides. In the presence of tunicamycin, asparagine-linked glycoproteins made in the endoplasmic reticulum are not glycosylated with N-linked glycans, and therefore may not fold correctly. Such proteins may be targeted for breakdown. Cells that are treated with tunicamycin normally experience an unfolded protein response and induce genes that encode endoplasmic reticulum chaperones such as the binding protein (BiP). We isolated a cDNA clone for Arabidopsis GPT and overexpressed it in Arabidopsis. The transgenic plants have a 10-fold higher level of GPT activity and are resistant to 1 microg/mL tunicamycin, a concentration that kills control plants. Transgenic plants grown in the presence of tunicamycin have N-glycosylated proteins and the drug does not induce BiP mRNA levels as it does in control plants. BiP mRNA levels are highly induced in both control and GPT-expressing plants by azetidine-2-carboxylate. These observations suggest that excess GPT activity obviates the normal unfolded protein response that cells experience when exposed to tunicamycin.
Koizumi
N
N
Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan.
Ujino
T
T
Sano
H
H
Chrispeels
M J
MJ
D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D001216:Asparagine / Q000378:metabolism*; D001483:Base Sequence; D017124:Conserved Sequence; D004351:Drug Resistance / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D006023:Glycoproteins / Q000096:biosynthesis*; D006031:Glycosylation; D007891:Leishmania / Q000201:enzymology; D051379:Mice; D008969:Molecular Sequence Data; D030821:Plants, Genetically Modified; D011134:Polysaccharides / Q000096:biosynthesis*; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D017855:Transferases (Other Substituted Phosphate Groups) / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology*
D006023:Glycoproteins; D011134:Polysaccharides; D011994:Recombinant Proteins; D014415:Tunicamycin; D001216:Asparagine; D017855:Transferases (Other Substituted Phosphate Groups); C106504:UDP-GlcNAc-undecaprenyl phosphate N-acetylglucosaminyl 1-phosphate transferase