An apoptotic inducer, aralin, is a novel type II ribosome-inactivating protein from Aralia elata.
We recently found that aralin, a novel cytotoxic protein consisting of two subunits, from Aralia elata selectively induces apoptosis in transformed cells as compared to normal cells. Here we report that aralin is a lectin specific for galactose (Gal) and its derivatives, and possesses RNA N-glycosidase activity as a new type II ribosome-inactivating protein (RIP). The RNA N-glycosidase activity of aralin was detected in cell-free and whole cell systems by the generation of an R-fragment from 28S rRNA. Coinciding with appearance of the R-fragment in aralin-treated cells, significant inhibition of protein synthesis was observed prior to the onset of apoptosis. Aralin-evoked cell death was efficiently repressed by the addition of Gal and its derivatives. Interestingly, melibiose preferentially protected normal cells from apoptosis as compared with transformed cells. Using rhodamine-coupled aralin, the aralin receptor could be clearly detected around the cell surface of transformed cells, but to a lesser extent on normal cells. Receptor binding was suppressed by Gal. These results indicate that aralin is incorporated into cells via its Gal-containing cell surface receptor and induces apoptosis through its RIP activity. Moreover, the expression level and/or structural changes of the aralin receptor may affect the sensitivity toward aralin.
Tomatsu
Makoto
M
Akita Research Institute of Food and Brewing, Arayamachi, Akita 010-1623, Japan. tomatsu@arif.pref.akita.jp
Kondo
Toshiya
T
Yoshikawa
Takafumi
T
Komeno
Takashi
T
Adachi
Naomi
N
Kawasaki
Yasushi
Y
Ikuta
Akira
A
Tashiro
Fumio
F
D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D027983:Aralia; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D037102:Lectins / Q000302:isolation & purification / Q000494:pharmacology*; D010936:Plant Extracts / Q000302:isolation & purification / Q000494:pharmacology; D010940:Plant Proteins / Q000302:isolation & purification / Q000494:pharmacology; D018520:Plant Shoots; D011500:Protein Synthesis Inhibitors / Q000302:isolation & purification / Q000494:pharmacology*; D051381:Rats; D054790:Ribosome Inactivating Proteins, Type 2; D012270:Ribosomes / Q000187:drug effects* / Q000378:metabolism
D037102:Lectins; D010936:Plant Extracts; D010940:Plant Proteins; D011500:Protein Synthesis Inhibitors; D054790:Ribosome Inactivating Proteins, Type 2; C488031:aralin