title: Caspase-3 activation is an early event and initiates apoptotic damage in a human leukemia cell line.
abstract: Many apoptotic pathways culminate in the activation of caspase cascades usually triggered by the apical caspases-8 or -9. We describe a paradigm where apoptosis is initiated by the effector caspase-3. Diethylmaleate (DEM)-induced apoptotic damage in Jurkat cells was blocked by the anti-apoptotic protein Bcl-2, whereas, a peptide inhibitor of caspase-3 but not caspase-9 blocked DEM-induced mitochondrial damage. Isogenic Jurkat cell lines deficient for caspase-8 or the adaptor FADD (Fas associated death domain) were not protected from DEM-induced apoptosis. Caspase-3 activation preceded that of caspase-9 and initial processing of caspase-3 was regulated independent of caspase-9 and Bcl-2. However, inhibitors of caspase-9 or caspase-6 regulated caspase-3 later in the pathway. We explored the mechanism by which caspase-3 processing is regulated in this system. DEM triggered a loss of Erk-1/2 phosphorylation and XIAP (X-linked inhibitor of apoptosis protein) expression. The phorbol ester PMA activated a MEK-dependent pathway to block caspase-3 processing and cell death. Constitutively active MEK-1 (CA-MEK) upregulated XIAP expression and exogenous XIAP inhibited DEM-induced apoptotic damage. Thus, we describe a pathway where caspase-3 functions to initiate apoptotic damage and caspase-9 and caspase-6 amplify the apoptotic cascade. Further, we show that MEK may regulate caspase-3 activation via the regulation of XIAP expression in these cells.
authors.affiliation: National Centre for Biological Sciences, New Bellary Road, UAS-GKVK Campus, Bangalore 560065, Karnataka, India.
authors.forename: J
authors.initials: J
authors.lastname: Varghese
authors.forename: N S
authors.initials: NS
authors.lastname: Khandre
authors.forename: A
authors.initials: A
authors.lastname: Sarin
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3; D053178:Caspase 6; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D019169:Jurkat Cells; D020935:MAP Kinase Signaling System / Q000502:physiology; D008298:Maleates / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D015853:Cysteine Proteinase Inhibitors; D008298:Maleates; D011506:Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D020928:Mitogen-Activated Protein Kinases; C505407:CASP3 protein, human; C505514:CASP6 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053178:Caspase 6; D053453:Caspase 9; D020169:Caspases; C014476:diethyl maleate