Selective involvement of BH3-only proteins and differential targets of Noxa in diverse apoptotic pathways.
The BH3-only proteins of the Bcl-2 family are known to mediate mitochondrial dysfunction during apoptosis. However, the identity of the critical BH3-only proteins and the mechanism of their action following treatment by diverse apoptotic stimuli remain to be fully resolved. We therefore used RNAi to screen the entire Bcl-2 family for their involvement in three major apoptotic pathways in HeLa cells. We found that Bcl-xL and Mcl-1 are major inhibitors of apoptosis induced by TNF-related apoptosis-inducing ligand (TRAIL), endoplasmic reticulum (ER) stress, and proteasome inhibition. Among the 10 BH3-only proteins, Bid and Noxa were found to be critically involved in TRAIL-induced apoptosis, in which Noxa participates by constitutively binding to Mcl-1. Bim and Noxa were found to be necessary for ER stress-induced apoptosis, in which Noxa assisted Bim function by sequestering Mcl-1 and binding to Bcl-xL. As a critical BH3-only protein, Noxa was strongly upregulated and became associated with both Mcl-1 and Bcl-xL during apoptosis induced by proteasome inhibition. In addition, we found that Noxa became 'Mcl-1 free' following treatment by ER stress and proteasome inhibition, but not after TRAIL treatment. These results defined the critical Bcl-2 network during apoptosis and suggested that Noxa participated in triggering mitochondrial dysfunction in multiple apoptotic pathways through distinct mechanisms.
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA.
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George
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D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D051023:BH3 Interacting Domain Death Agonist Protein / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D004721:Endoplasmic Reticulum / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D061988:Proteasome Inhibitors; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D013312:Stress, Physiological; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C494819:BAD protein, human; C494772:BAK1 protein, human; C494826:BAX protein, human; C438378:BBC3 protein, human; C494811:BCL2L1 protein, human; C000606775:BCL2L11 protein, human; C491073:BCL2L2 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C090121:BNIP3 protein, human; D000072224:Bcl-2-Like Protein 11; D007976:Leupeptins; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C498702:PMAIP1 protein, human; D061988:Proteasome Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; D019284:Thapsigargin; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde