The mitochondrial apoptosis-inducing factor plays a role in E2F-1-induced apoptosis in human colon cancer cells.
BACKGROUND
Overexpression of the transcription factor E2F-1 provokes apoptosis in cancer cells; the mechanism, however, is not completely understood. We sought to evaluate E2F-1 gene therapy in human colon cancer and to investigate the apoptotic pathway involved.


METHODS
Adenoviral vectors were used to transfect the E2F-1 gene (Ad5E2F-1) or the control gene luciferase (Ad5Luc) into four human colon carcinoma cell lines. Apoptosis was confirmed by flow cytometry and poly (ADP-ribose) polymerase cleavage. Expression of apoptotic factors was determined with Western blot analysis. Inhibitory assays were used to determine the involvement of caspases in the apoptotic pathway.


RESULTS
Overexpression of E2F-1 was evident in all cells treated with Ad5E2F-1; upregulation of Bcl-2, and activation of caspases were noted. The apoptosis-inducing factor in the cytosolic fraction was markedly upregulated after Ad5E2F-1 treatment. E2F-1 overexpression inhibited proliferation and induced significant apoptosis in all cell lines (P <.005). This apoptotic response could be only partially blocked by caspase inhibitors.


CONCLUSIONS
These findings demonstrate that E2F-1 induces apoptosis and inhibits proliferation in human colon cancer cell lines. The marked upregulation of apoptosis-inducing factor and the fact that E2F-1-induced apoptosis is incompletely blocked by caspase inhibitors suggest a caspase-independent pathway of E2F-1-mediated apoptosis, reported here for the first time.
Vorburger
Stephan A
SA
Department of Surgical Oncology, University of Texas, M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Pataer
Abujiang
A
Yoshida
Kazumi
K
Liu
Yanna
Y
Lu
Xiaolin
X
Swisher
Stephen G
SG
Hunt
Kelly K
KK
D000256:Adenoviridae; D017209:Apoptosis / Q000187:drug effects*; D051033:Apoptosis Inducing Factor; D002277:Carcinoma / Q000503:physiopathology*; D020169:Caspases / Q000494:pharmacology; D018797:Cell Cycle Proteins; D002455:Cell Division; D003110:Colonic Neoplasms / Q000503:physiopathology*; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005420:Flavoproteins / Q000494:pharmacology*; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D015316:Genetic Therapy; D006801:Humans; D008156:Luciferases / Q000235:genetics; D008565:Membrane Proteins / Q000494:pharmacology*; D014157:Transcription Factors / Q000494:pharmacology*; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
C494829:AIFM1 protein, human; D051033:Apoptosis Inducing Factor; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D005420:Flavoproteins; D008565:Membrane Proteins; D014157:Transcription Factors; D008156:Luciferases; D020169:Caspases