title: Ectopic expression of Bcl-XL or Ku70 protects human colon cancer cells (SW480) against curcumin-induced apoptosis while their down-regulation potentiates it.
abstract: Curcumin, the yellow pigment derived from Curcuma longa, is known to induce apoptosis of several cancer cells. However, many cancer cells protect themselves by over-expressing antiapoptotic proteins such as Bcl-XL or Ku70. To study their role in curcumin-induced apoptosis, human colon cancer cells (SW480) were made to over-express or under-express Bcl-XL (by stable transfection) and Ku70 (by transient transfection) using plasmid constructs that express their genes in sense or antisense orientation, respectively. Stable cells that express Bax [Bax-GFP (green fluorescent protein)], a proapoptotic member of the Bcl-2 family, were also established. Curcumin-induced cell death and nuclear condensation was more in AsBcl-XL and AsKu70 cells that under-express Bcl-XL and Ku70, respectively, compared with the vector-transfected cells. Bcl-XL and Ku70 protected the cells by inhibiting the release of cytochrome c, Smac (second mitochondria derived activator of caspase) and apoptosis inducing factor (AIF), and the activation of caspases 9, 8 and 3 triggered by curcumin. AsBcl-XL and AsKu70 cells were more sensitive to curcumin through enhanced activation of caspases 9 and 3 and release of cytochrome c, Smac and AIF. Curcumin-induced activation of caspase 8 was blocked by Ku70 but not by Bcl-XL. However, caspase 8 activation by curcumin was accelerated in both AsBcl-XL and AsKu70 cells suggesting a possible feedback activation of caspase 8 by caspase 3. Bax-GFP cells were highly sensitized when Ku70 was down-regulated supporting the reported role of Ku70 in the retention of Bax within the cytosol. The study reveals the potential of antisense inhibition of antiapoptotic proteins as an effective strategy to tackle chemoresistant cancers with curcumin.
authors.affiliation: Division of Cancer Biology, Rajiv Gandhi Center for Biotechnology, Thiruvananthapuram, Kerala 695014, India.
authors.forename: Ramachandran
authors.initials: R
authors.lastname: Rashmi
authors.forename: Santhosh
authors.initials: S
authors.lastname: Kumar
authors.forename: Devarajan
authors.initials: D
authors.lastname: Karunagaran
mesh_terms: D034961:Antigens, Nuclear / Q000378:metabolism*; 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; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015536:Down-Regulation; D004789:Enzyme Activation / Q000187:drug effects; D005420:Flavoproteins / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006023:Glycoproteins / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D000072200:Ku Autoantigen; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: C494829:AIFM1 protein, human; D034961:Antigens, Nuclear; D000970:Antineoplastic Agents; D051033:Apoptosis Inducing Factor; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D061945:Caspase Inhibitors; D015938:Complement Membrane Attack Complex; D004268:DNA-Binding Proteins; D005420:Flavoproteins; D006023:Glycoproteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C047610:SC5b-9 protein complex; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D049452:Green Fluorescent Proteins; D003165:Complement System Proteins; D045304:Cytochromes c; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D003474:Curcumin