BTB domain-containing speckle-type POZ protein (SPOP) serves as an adaptor of Daxx for ubiquitination by Cul3-based ubiquitin ligase.
Daxx is a multifunctional protein that regulates a variety of cellular processes, including transcription, cell cycle, and apoptosis. SPOP is a BTB (Bric-a-brac/Tramtrack/Broad complex) protein that constitutes Cul3-based ubiquitin ligases. Here we show that SPOP serves as an adaptor of Daxx for the ubiquitination by Cul3-based ubiquitin ligase and subsequent degradation by the proteasome. Expression of SPOP with Cul3 markedly reduced Daxx level, and this degradation was blocked by SPOP-specific short hairpin RNAs. Inhibition of the proteasome by MG132 caused the prevention of Daxx degradation in parallel with the accumulation of ubiquitinated Daxx. Expression of SPOP with Cul3 reversed Daxx-mediated repression of ETS1- and p53-dependent transcription, and short hairpin RNA-mediated knock down of SPOP blocked the recovery of their transcriptional activation. Furthermore, Daxx degradation led to the cleavage of poly(ADP-ribose) polymerase and the increase in the number of terminal deoxynucleotidyltransferase-mediated dUTP-fluorescein nick end-labeling-positive apoptotic cells. These results suggest that SPOP/Cul3-ubiquitin ligase plays an essential role in the control of Daxx level and, thus, in the regulation of Daxx-mediated cellular processes, including transcriptional regulation and apoptosis.
Kwon
Jeong Eun
JE
NRL of Protein Biochemistry, School of Biological Sciences, Seoul National University, Seoul 151-742, Korea.
La
Muhnho
M
Oh
Kyu Hee
KH
Oh
Young Mi
YM
Kim
Gi Ryang
GR
Seol
Jae Hong
JH
Baek
Sung Hee
SH
Chiba
Tomoki
T
Tanaka
Keiji
K
Bang
Ok Sun
OS
Joe
Cheol O
CO
Chung
Chin Ha
CH
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D019556:COS Cells; D018797:Cell Cycle Proteins / Q000737:chemistry*; D002522:Chlorocebus aethiops; D056970:Co-Repressor Proteins; D044842:Cullin Proteins / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D018832:Molecular Chaperones; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025801:Ubiquitin / Q000737:chemistry*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry*
D048868:Adaptor Proteins, Signal Transducing; C503645:CUL3 protein, human; D018797:Cell Cycle Proteins; D056970:Co-Repressor Proteins; D044842:Cullin Proteins; C106985:DAXX protein, human; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D012097:Repressor Proteins; C509761:SPOP protein, human; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex