Involvement of an SCFSlmb complex in timely elimination of E2F upon initiation of DNA replication in Drosophila.
BACKGROUND
Cul1 is a core component of the evolutionarily conserved SCF-type ubiquitin ligases that target specific proteins for destruction. SCF action contributes to cell cycle progression but few of the key targets of its action have been identified.


RESULTS
We found that expression of the mouse Cul1 (mCul1) in the larval wing disc has a dominant negative effect. It reduces, but does not eliminate, the function of SCF complexes, promotes accumulation of Cubitus interruptus (a target of SCF action), triggers apoptosis, and causes a small wing phenotype. A screen for mutations that dominantly modify this phenotype showed effective suppression upon reduction of E2F function, suggesting that compromised downregulation of E2F contributes to the phenotype. Partial inactivation of Cul1 delayed the abrupt loss of E2F immunofluorescence beyond its normal point of downregulation at the onset of S phase. Additional screens showed that mild reduction in function of the F-box encoding gene slimb enhanced the mCul1 overexpression phenotype. Cell cycle modulation of E2F levels is virtually absent in slimb mutant cells in which slimb function is severely reduced. This implicates Slimb, a known targeting subunit of SCF, in E2F downregulation. In addition, Slimb and E2F interacted in vitro in a phosphorylation-dependent manner.


CONCLUSIONS
We have used genetic and physical interactions to identify the G1/S transcription factor E2F as an SCFSlmb target in Drosophila. These results argue that the SCFSlmb ubiquitin ligase directs E2F destruction in S phase.
Hériché
Jean-Karim
JK
Department of Biochemistry and Biophysics, University of California, San Francisco, 513 Parnassus Street, San Francisco, CA 94143-0448, USA. heriche@cgl.ucsf.edu
Ang
Dan
D
Bier
Ethan
E
O'Farrell
Patrick H
PH
D000818:Animals; D030801:Animals, Genetically Modified; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D044842:Cullin Proteins / Q000235:genetics / Q000502:physiology; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015536:Down-Regulation; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D050684:E2F Transcription Factors; D005260:Female; D018507:Gene Expression Regulation, Developmental; D008297:Male; D051379:Mice; D009154:Mutation; D011485:Protein Binding; D016196:S Phase / Q000235:genetics / Q000502:physiology; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D014921:Wings, Animal / Q000254:growth & development / Q000378:metabolism
D018797:Cell Cycle Proteins; C100318:Cullin 1; D044842:Cullin Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D050684:E2F Transcription Factors; D014157:Transcription Factors; C110233:slmb protein, Drosophila; D044843:SKP Cullin F-Box Protein Ligases; D044767:Ubiquitin-Protein Ligases