The F-box protein Skp2 is a ubiquitylation target of a Cul1-based core ubiquitin ligase complex: evidence for a role of Cul1 in the suppression of Skp2 expression in quiescent fibroblasts.
The ubiquitin protein ligase SCF(Skp2) is composed of Skp1, Cul1, Roc1/Rbx1 and the F-box protein Skp2, the substrate-recognition subunit. Levels of Skp2 decrease as cells exit the cell cycle and increase as cells re-enter the cycle. Ectopic expression of Skp2 in quiescent fibroblasts causes mitogen-independent S-phase entry. Hence, mechanisms must exist for limiting Skp2 protein expression during the G(0)/G(1) phases. Here we show that Skp2 is degraded by the proteasome in G(0)/G(1) and is stabilized when cells re-enter the cell cycle. Rapid degradation of Skp2 in quiescent cells depends on Skp2 sequences that contribute to Cul1 binding and interference with endogenous Cul1 function in serum-deprived cells induces Skp2 expression. Furthermore, recombinant Cul1-Roc1/Rbx1-Skp1 complexes can catalyse Skp2 ubiquitylation in vitro. These results suggest that degradation of Skp2 in G(0)/G(1) is mediated, at least in part, by an autocatalytic mechanism involving a Skp2-bound Cul1-based core ubiquitin ligase and imply a role for this mechanism in the suppression of SCF(Skp2) ubiquitin protein ligase function during the G(0)/G(1) phases of the cell cycle.
Wirbelauer
C
C
Friedrich Miescher Institut, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.
Sutterlüty
H
H
Blondel
M
M
Gstaiger
M
M
Peter
M
M
Reymond
F
F
Krek
W
W
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D044842:Cullin Proteins; D016895:Culture Media, Serum-Free; D003546:Cysteine Endopeptidases / Q000378:metabolism; D005347:Fibroblasts; D005816:Genetic Complementation Test; D006801:Humans; D008025:Ligases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D021122:Protein Subunits; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D013489:Suppression, Genetic / Q000235:genetics; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*; D015003:Yeasts / Q000235:genetics / Q000254:growth & development
C100988:Cdc53 protein, S cerevisiae; D018797:Cell Cycle Proteins; C100318:Cullin 1; D044842:Cullin Proteins; D016895:Culture Media, Serum-Free; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D021122:Protein Subunits; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008025:Ligases