Transcriptional squelching by ectopic expression of E2F-1 and p53 is alleviated by proteasome inhibitors MG-132 and lactacystin.
The transcription factors p53 and E2F-1 play important roles in the control of cell cycle progression. In transient transfection experiments, expression of E2F-1, other E2F family members, or p53 squelched transcription from cotransfected plasmids in a dose-dependent manner. Although the proteasome inhibitors MG-132 and lactacystin markedly increased the level of expression of E2F-1 and p53, these inhibitors completely alleviated squelching by both proteins. Several observations indicate MG-132 alleviates squelching by influencing the conformation of newly synthesized p53 and E2F-1:MG-132 increased the fraction of wild type p53 bound by a monoclonal antibody which preferentially recognizes mutant conformers of p53, increased binding of hsp70 to p53 and inhibited nuclear accumulation of both p53 and E2F-1, but not the pocket protein p107. The protease inhibitors ALLN and ALLM did not influence expression of E2F-1 or p53, nor did they alleviate squelching by either transcription factor. Because MG-132 and lactacycstin are highly specific inhibitors of the proteasome protease, our results suggest that the proteasome influences post-translational processes involved in proper folding and cytoplasmic clearing of E2F-1 and p53.
Magae
J
J
Department of Pathology, University of Vermont, Burlington 05405, USA.
Illenye
S
S
Tejima
T
T
Chang
Y C
YC
Mitsui
Y
Y
Tanaka
K
K
Omura
S
S
Heintz
N H
NH
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D016466:CHO Cells; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D003513:Cycloheximide / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D007976:Leupeptins / Q000378:metabolism* / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects*; D015533:Transcriptional Activation; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D007976:Leupeptins; D009842:Oligopeptides; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D014452:Ubiquitins; C063261:acetylleucyl-leucyl-norleucinal; C069861:calpain inhibitor 2; C067713:lactacystin; D003513:Cycloheximide; D001616:beta-Galactosidase; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine