FAT10, a ubiquitin-independent signal for proteasomal degradation.
FAT10 is a small ubiquitin-like modifier that is encoded in the major histocompatibility complex and is synergistically inducible by tumor necrosis factor alpha and gamma interferon. It is composed of two ubiquitin-like domains and possesses a free C-terminal diglycine motif that is required for the formation of FAT10 conjugates. Here we show that unconjugated FAT10 and a FAT10 conjugate were rapidly degraded by the proteasome at a similar rate. Fusion of FAT10 to the N terminus of very long-lived proteins enhanced their degradation rate as potently as fusion with ubiquitin did. FAT10-green fluorescent protein fusion proteins were not cleaved but entirely degraded, suggesting that FAT10-specific deconjugating enzymes were not present in the analyzed cell lines. Interestingly, the prevention of ubiquitylation of FAT10 by mutation of all lysines or by expression in ubiquitylation-deficient cells did not affect FAT10 degradation. Thus, conjugation with FAT10 is an alternative and ubiquitin-independent targeting mechanism for degradation by the proteasome, which, in contrast to polyubiquitylation, is cytokine inducible and irreversible.
Hipp
Mark Steffen
MS
Universität Konstanz, Fachbereich Biologie/Immunologie, P1101, Universitätsstrasse 10, D-78457 Konstanz, Germany.
Kalveram
Birte
B
Raasi
Shahri
S
Groettrup
Marcus
M
Schmidtke
Gunter
G
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002460:Cell Line; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006207:Half-Life; D006801:Humans; D051379:Mice; D009154:Mutation / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology; D014162:Transfection; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C430242:NUB1 protein, human; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C109184:UBD protein, human; D025801:Ubiquitin; D014452:Ubiquitins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex