Apoptosis induction by activator protein 2alpha involves transcriptional repression of Bcl-2.
Activator protein 2alpha (AP-2alpha) induces cytotoxicity by inducing cell cycle arrest and apoptosis. In this study we investigated the mechanism of apoptosis induction by AP-2alpha. We found that AP-2alpha induced apoptosis efficiently in cells treated with benzyloxycar-bonyl-IETD-fluoromethyl ketone or FADD-silenced cells but failed to do so in benzyloxycarbonyl-LEHD-fluoromethyl ketone-treated or apoptosis protease activation factor-1 (Apaf1)-silenced cells, suggesting the central role of mitochondria in AP-2alpha-induced apoptosis. In good correlation, cells overexpressing AP-2alpha showed a reduction in mitochondrial membrane potential (Deltapsi(m)), cytochrome c and Smac/DIABLO release into cytosol, and Bax translocation into mitochondria. We found that the pro-apoptotic protein Bax is important for AP-2alpha-induced apoptosis as adenovirus AP2 failed to induce apoptosis in HCT116 Bax(-/-) cells. However, we found the IAP (inhibitor of apoptosis) inhibitor Smac/DIABLO may have a limited role in AP-2alpha-induced apoptosis as we found the IAP member Survivin down-regulated by AP-2alpha. Although the total Bax level remains unaltered, we found a time-dependent increase in the activated form of Bax in adenovirus AP2-infected cells. In addition, we show that AP-2alpha transcriptionally represses Bcl-2 by binding to its promoter both in vitro and in vivo and that this is essential for AP-2alpha-induced apoptosis as ectopic expression of Bcl-2 efficiently inhibited apoptosis induced by AP-2alpha. Furthermore, we show that chemotherapy-induced endogenous AP-2alpha down-regulates Bcl-2 and induces apoptosis in an AP-2alpha-dependent manner. Moreover, we demonstrate that inhibition of okadaic acid or staurosporine-sensitive pathways in AP-2alpha overexpressing breast cancer cells resulted in AP-2alpha-dependent apoptosis induction. These results suggest that AP-2alpha induces apoptosis by down-regulating Bcl-2 and utilizing a bax/cytochrome c/Apaf1/caspase 9-dependent mitochondrial pathway.
Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560 012, India.
Narendra
N
Wajapeyee
Ramona
R
Britto
Halasahalli M
HM
Ravishankar
Kumaravel
K
Somasundaram
D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000378:metabolism; D015536:Down-Regulation; D005786:Gene Expression Regulation; D020868:Gene Silencing; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008564:Membrane Potentials; D024101:Mitochondrial Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D015398:Signal Transduction; D050656:Transcription Factor AP-2 / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D050656:Transcription Factor AP-2; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c