c-Myc and caspase-2 are involved in activating Bax during cytotoxic drug-induced apoptosis.
Activation of Bax following diverse cytotoxic stress has been shown to be an essential gateway to mitochondrial dysfunction and activation of the intrinsic apoptotic pathway characterized by cytochrome c release with caspase-9/-3 activation. Interestingly, c-Myc has been reported to promote apoptosis by destabilizing mitochondrial integrity in a Bax-dependent manner. Stress-induced activation of caspase-2 may also induce permeabilization of mitochondria with activation of the intrinsic death pathway. To test whether c-Myc and caspase-2 cooperate to activate Bax and thereby mediate intrinsic apoptosis, small interfering RNA was used to efficiently knock down the expression of c-Myc, caspase-2, and Apaf-1, an activating component in the apoptosome, in two human cancer cell lines, lung adenocarcinoma A-549 and osteosarcoma U2-OS cells. Under conditions when the expression of endogenous c-Myc, caspase-2, or Apaf-1 is reduced 80-90%, cisplatin (or etoposide)-induced apoptosis is significantly decreased. Biochemical studies reveal that the expression of c-Myc and caspase-2 is crucial for cytochrome c release from mitochondria during cytotoxic stress and that Apaf-1 is only required following cytochrome c release to activate caspases-9/-3. Although knockdown of c-Myc or caspase-2 does not affect Bax expression, caspase-2 is important for cytosolic Bax to integrate into the outer mitochondrial membrane, and c-Myc is critical for oligomerization of Bax once integrated into the membrane.
Cao
Xuefang
X
University of Florida Shands Cancer Center and Department of Medicine, University of Florida College of Medicine, Gainesville, FL 32610, USA.
Bennett
Richard L
RL
May
W Stratford
WS
D017209:Apoptosis / Q000187:drug effects*; D053477:Apoptotic Protease-Activating Factor 1 / Q000235:genetics / Q000378:metabolism; D053143:Caspase 2 / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D006801:Humans; D051336:Mitochondrial Membranes / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; C494826:BAX protein, human; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D034741:RNA, Small Interfering; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; C490360:CASP2 protein, human; D053143:Caspase 2; D003546:Cysteine Endopeptidases; D002945:Cisplatin