A transcriptionally inactive E2F-1 targets the MDM family of proteins for proteolytic degradation.
E2F-1-activated transcription promotes cell cycle progression and apoptosis. These functions are regulated by several factors including the E2F-1-binding protein MDM2 and the retinoblastoma protein pRb. Using a yeast two-hybrid screen we have identified the MDM2-related protein, MDMX, as an E2F-1-binding protein. In these studies we find that coexpression of MDMX with E2F-1 results in degradation of the MDMX protein. Although this proteolytic degradation can be blocked by the protease inhibitors bafilomycin A(1), N-acetyl-Leu-Leu-Norleu-AL, and N-acetyl-Leu-Leu-Met-AL, MDMX degradation is not inhibited by lactacystin, suggesting that degradation occurs by a proteasome-independent mechanism. Using an E2F-1 deletion mutant (E2F-1(180-437)) we show that E2F-1-targeted degradation of MDMX does not require the E2F-1 DNA binding domain and therefore is independent of E2F-1-driven transcription. We also find that this transcriptionally inactive E2F-1 mutant is capable of degrading the MDMX-related protein MDM2 and the MDMX isoform MDMX-S. Mapping of the E2F-1 C terminus reveals that neither a previously characterized C-terminal MDM2 binding domain nor the pRb binding domain on E2F-1 is required for MDMX and MDM2 degradation.
Strachan
G D
GD
Department of Orthopedic Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Rallapalli
R
R
Pucci
B
B
Lafond
T P
TP
Hall
D J
DJ
D001483:Base Sequence; D018797:Cell Cycle Proteins; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D017931:DNA Primers; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D006801:Humans; D006868:Hydrolysis; D009097:Multienzyme Complexes / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D046988:Proteasome Endopeptidase Complex; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques
D018797:Cell Cycle Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex