Isoform- and cell cycle-dependent substrate degradation by the Fbw7 ubiquitin ligase.
The SCF(FBW7) ubiquitin ligase degrades proteins involved in cell division, growth, and differentiation and is commonly mutated in cancers. The Fbw7 locus encodes three protein isoforms that occupy distinct subcellular localizations, suggesting that each has unique functions. We used gene targeting to create isoform-specific Fbw7-null mutations in human cells and found that the nucleoplasmic Fbw7alpha isoform accounts for almost all Fbw7 activity toward cyclin E, c-Myc, and sterol regulatory element binding protein 1. Cyclin E sensitivity to Fbw7 varies during the cell cycle, and this correlates with changes in cyclin E-cyclin-dependent kinase 2 (CDK2)-specific activity, cyclin E autophosphorylation, and CDK2 inhibitory phosphorylation. These data suggest that oscillations in cyclin E-CDK2-specific activity during the cell cycle regulate the timing of cyclin E degradation. Moreover, they highlight the utility of adeno-associated virus-mediated gene targeting in functional analyses of complex loci.
Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
Jonathan E
JE
Grim
Michael P
MP
Gustafson
Roli K
RK
Hirata
Amanda C
AC
Hagar
Jherek
J
Swanger
Markus
M
Welcker
Harry C
HC
Hwang
Johan
J
Ericsson
David W
DW
Russell
Bruce E
BE
Clurman
D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D004795:Enzyme Stability; D044783:F-Box Proteins / Q000378:metabolism*; D000073979:F-Box-WD Repeat-Containing Protein 7; D018390:Gene Targeting; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D051780:Sterol Regulatory Element Binding Protein 1 / Q000378:metabolism; D013379:Substrate Specificity; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
D018797:Cell Cycle Proteins; D019927:Cyclin E; D044783:F-Box Proteins; D000073979:F-Box-WD Repeat-Containing Protein 7; C513273:FBXW7 protein, human; D007527:Isoenzymes; D016271:Proto-Oncogene Proteins c-myc; C497387:SREBF1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; D044767:Ubiquitin-Protein Ligases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2