title: Mechanism of ricin-induced apoptosis in human cervical cancer cells.
abstract: The mechanism of ricin-induced apoptosis in human cervical cancer cell line HeLa was studied. The present study demonstrated that ricin induces apoptosis of human cervical cancer cells (HeLa) in a time dependent manner with an IC(50) for cell viability of 1 microg/ml. Ricin treatment resulted in a time dependent increase in LDH leakage, DNA fragmentation, percent apoptotic cells, generation of reactive oxygen species and depletion of intracellular glutathione levels. DNA agarose gel electrophoresis showed typical oligonucleosomal length DNA fragmentation. Additionally, DNA diffusion assay was performed to confirm DNA damage and apoptosis. Ricin activated caspase-3 as evidenced by both proteolytic cleavage of procaspase-3 into 20 and 18 kDa subunits, and increased protease activity. Caspase activity was maximum at 4h and led to the cleavage of 116 kDa poly(ADP-ribose) polymerase (PARP), resulting in the 85 kDa cleavage product. Ricin-induced caspase-3 activation also resulted in cleavage of DNA fragmentation factor-45 (DFF45/ICAD) and DFF40 or caspase-activated DNase in HeLa cells. Activation of caspase-3, cleavage of PARP and DNA fragmentation was blocked by pre-treatment with caspase-3 specific inhibitor Ac-DEVD-CHO (100 microM) and broad-spectrum caspase inhibitor Z-VAD-FMK (40 microM). Ricin-induced DNA fragmentation was inhibited by pre-treatment with PARP inhibitors 3-aminobenzamide (100 microM) and DPQ (10 microM). Our results indicate that ricin-induced cell death was mediated by generation of reactive oxygen species and subsequent activation of caspase-3 cascade followed by down stream events leading to apoptotic mode of cell death.
authors.affiliation: Division of Pharmacology and Toxicology, Defence Research and Development Establishment, Jhansi Road, Gwalior 474002, India. pvlrao@rediffmail.com
authors.forename: P V Lakshmana
authors.initials: PV
authors.lastname: Rao
authors.forename: R
authors.initials: R
authors.lastname: Jayaraj
authors.forename: A S B
authors.initials: AS
authors.lastname: Bhaskar
authors.forename: Om
authors.initials: O
authors.lastname: Kumar
authors.forename: R
authors.initials: R
authors.lastname: Bhattacharya
authors.forename: Parag
authors.initials: P
authors.lastname: Saxena
authors.forename: P K
authors.initials: PK
authors.lastname: Dash
authors.forename: R
authors.initials: R
authors.lastname: Vijayaraghavan
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D018384:Oxidative Stress; D011065:Poly(ADP-ribose) Polymerases / Q000502:physiology; D012276:Ricin / Q000494:pharmacology*
chemical_list: D012276:Ricin; D011065:Poly(ADP-ribose) Polymerases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D005978:Glutathione