Regulation and deregulation of E2F1 in postmitotic neurons differentiated from embryonal carcinoma P19 cells.
Neurons withdraw from the cell cycle immediately after differentiation from their proliferative precursors. E2F1, a principal transcription factor that promotes cell cycle progression, must be silenced in neurons. We investigated the E2F1 system in postmitotic neurons derived from murine embryonal carcinoma P19 cells. P19 cells highly expressed the E2F1 gene during neural differentiation, and enriched neurons contained a high abundance of E2F1 mRNA. In contrast, postmitotic neurons possessed extremely low levels of E2F1 protein as assessed by the electrophoretic mobility shift assay and Western blotting. A recombinant E2F1 fusion protein was ubiquitinated in vitro when incubated with neuronal lysates. In addition, treatment with the proteasome inhibitor MG132 increased the endogenous level of E2F1 protein in neurons. These results suggest that the ubiquitin-proteasome pathway contributes, at least in part, to the downregulation of E2F1 protein in postmitotic neurons. Adenovirus-mediated transfer of E2F1 cDNA into postmitotic neurons induced both bromodeoxyuridine incorporation and chromatin condensation, suggesting that deregulated E2F1 expression causes both aberrant S-phase entry and apoptosis of postmitotic neurons. Thus, downregulation of endogenous E2F1 protein in postmitotic neurons may be indispensable for the prevention of their reentry into the cell cycle.
Azuma-Hara
M
M
Division of Regulation of Macromolecular Functions, Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka, 565-0871, Japan.
Taniura
H
H
Uetsuki
T
T
Niinobe
M
M
Yoshikawa
K
K
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis; D018236:Carcinoma, Embryonal; D002352:Carrier Proteins; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D003546:Cysteine Endopeptidases / Q000187:drug effects; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005786:Gene Expression Regulation; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D008938:Mitosis / Q000502:physiology; D009097:Multienzyme Complexes / Q000187:drug effects; D009474:Neurons / Q000473:pathology*; D046988:Proteasome Endopeptidase Complex; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000032:analysis; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase / Q000502:physiology; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D014407:Tumor Cells, Cultured; D014452:Ubiquitins / Q000378:metabolism
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D007976:Leupeptins; D009097:Multienzyme Complexes; D012333:RNA, Messenger; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D014452:Ubiquitins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D007930:Leucine; C024974:E 64; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde