Human colon cancer cells lacking Bax resist curcumin-induced apoptosis and Bax requirement is dispensable with ectopic expression of Smac or downregulation of Bcl-XL.
Multiple apoptotic stimuli induce conformational changes in Bax, a proapoptotic protein from the Bcl-2 family and its deficiency is a frequent cause of chemoresistance in colon adenocarcinomas. Curcumin, a dietary compound from turmeric, is known to induce apoptosis in a variety of cancer cells. To understand the role of Bax in curcumin-induced apoptosis we used HCT116 human colon cancer cells with one allele of Bax gene (Bax+/-) and Bax knockout HCT116 (Bax-/-) cells in which Bax gene is inactivated by homologous recombination. Cell viability decreased in a concentration-dependent manner in Bax+/- cells treated with curcumin (0-50 microM) whereas only minimal changes in viability were observed in Bax-/- cells upon curcumin treatment. In Bax-/- cells curcumin-induced activation of caspases 9 and 3 was blocked and that of caspase 8 remained unaltered. Curcumin-induced release of cytochrome c, Second mitochondria derived activator of caspase (Smac) and apoptosis inducing factor (AIF) was also blocked in Bax-/- cells and reintroduction of Bax, downregulation of the antiapoptotic protein Bcl-XL by antisense DNA as well as the overexpression of Smac, highly sensitized the Bax-/- cells toward curcumin-induced apoptosis. There was no considerable difference in the percentage of apoptotic cells in Bak RNAi transfected Bax+/- or Bax-/- cells treated with curcumin when compared with their corresponding vector transfected cells treated with curcumin. The present study demonstrates the role of Bax but not Bak as a critical regulator of curcumin-induced apoptosis and implies the potential of targeting antiapoptotic proteins like Bcl-XL or overexpression of proapoptotic proteins like Smac as interventional approaches to deal with Bax-deficient chemo-resistant cancers for curcumin-based therapy.
Rashmi
Ramachandran
R
Cancer Biology Laboratory, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, Kerala 695 014, India.
Kumar
Santhosh
S
Karunagaran
Devarajan
D
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D051033:Apoptosis Inducing Factor; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins; D003474:Curcumin / Q000494:pharmacology*; D045304:Cytochromes c / Q000378:metabolism; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation / Q000187:drug effects; D005420:Flavoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006023:Glycoproteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
C494829:AIFM1 protein, human; D000970:Antineoplastic Agents; D051033:Apoptosis Inducing Factor; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D061945:Caspase Inhibitors; D015938:Complement Membrane Attack Complex; D005420:Flavoproteins; D006023:Glycoproteins; D008565:Membrane Proteins; D016376:Oligonucleotides, Antisense; D019253:Proto-Oncogene Proteins c-bcl-2; C047610:SC5b-9 protein complex; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D003165:Complement System Proteins; D045304:Cytochromes c; D020169:Caspases; D003474:Curcumin