Transfer of E2F-1 to human glioma cells results in transcriptional up-regulation of Bcl-2.
Strong evidence exists to support the tenet that activation of E2F transcription factors, via alterations in the p16-cyclin D-Rb pathway, is a key event in the malignant progression of most human malignant gliomas. The oncogenic ability of E2F has been related to the E2F-mediated up-regulation of several proteins that positively regulate cell proliferation. However, E2F may indirectly enhance proliferation by activating antiapoptotic molecules. In this work, we sought to ascertain whether E2F-1-mediated events involve the up-regulation of the antiapoptotic molecule Bcl-2. Western blot analyses showed up-regulation of Bcl-2 but not of Bcl-x(L) by 24 h after the transfer of E2F-1. Northern blot studies showed that transfer of E2F-1 also up-regulated Bcl-2 RNA. In support of these findings and the concept that E2F-1 has a direct effect in the induction of Bcl-2, we found a putative E2F binding site within the Bcl-2 sequence. Subsequent gel-mobility shift and supershift experiments involving the CTCCGCGC site in the bcl-2 promoter showed that E2F-1 bound Bcl-2. Transactivation experiments consistently showed that ectopic E2F-1 activated responsive elements located in the -1448/-1441 region in the P1 promoter region of the bcl-2 gene. As expected, other members of the E2F family of transcription factors such as E2F-2 and E2F-4 also transactivated the bcl-2 promoter. Our results demonstrate that E2F-1 modulates the expression of the antiapoptotic molecule Bcl-2 and suggest that up-regulation of Bcl-2 may favor the oncogenic role of E2F-1 and other members of the E2F family of transcription factors.
Gomez-Manzano
C
C
Department of Neuro-Oncology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030, USA.
Mitlianga
P
P
Fueyo
J
J
Lee
H Y
HY
Hu
M
M
Spurgers
K B
KB
Glass
T L
TL
Koul
D
D
Liu
T J
TJ
McDonnell
T J
TJ
Yung
W K
WK
D001665:Binding Sites; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D050704:E2F4 Transcription Factor; D015972:Gene Expression Regulation, Neoplastic; D018014:Gene Transfer Techniques; D019254:Genes, bcl-2 / Q000235:genetics; D005910:Glioma / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D011401:Promoter Regions, Genetic; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics*; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D015533:Transcriptional Activation; D015854:Up-Regulation
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050703:E2F2 Transcription Factor; C493761:E2F2 protein, human; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D014157:Transcription Factors