A degradation signal located in the C-terminus of p21WAF1/CIP1 is a binding site for the C8 alpha-subunit of the 20S proteasome.
The cyclin-dependent kinase inhibitor p21WAF1/CIP1 is a key regulator of cell-cycle progression and its expression is tightly regulated at the level of transcription and by proteasome-dependent proteolysis. The turnover of p21WAF1/CIP1 by proteasomes does not always require the ubiquitylation of p21WAF1/CIP1 suggesting that there could be an alternative pathway into the proteasome. Here we show that the C8 alpha-subunit of the 20S proteasome interacts with the C-terminus of p21WAF1/CIP1 and mediates the degradation of p21WAF1/CIP1. A small deletion in this region that disrupts binding to C8 increased the half-life of p21WAF1/CIP1 expressed in vivo. In contrast a deletion that increased the affinity between C8 and p21WAF1/CIP1 significantly reduced the stability of the latter. These data suggest that interaction with a 20S proteasome alpha-subunit is a critical determinant of p21WAF1/CIP1 turn-over and show how non-ubiquitylated molecules might bypass the 19S regulator of the proteasome and become targeted directly to the 20S, core protease. Consistent with this, p21WAF1/CIP1 was degraded rapidly by purified 20S proteasomes in a manner that was dependent on the C8-interaction domain.
Touitou
R
R
Virology and Cell Biology and Ludwig Institute for Cancer Research, Imperial College of Science, Technology and Medicine, Norfolk Place, London W2 1PG, UK.
Richardson
J
J
Bose
S
S
Nakanishi
M
M
Rivett
J
J
Allday
M J
MJ
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D014407:Tumor Cells, Cultured
C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009097:Multienzyme Complexes; D018809:Proliferating Cell Nuclear Antigen; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex