Conformational change and mitochondrial translocation of Bax accompany proteasome inhibitor-induced apoptosis of chronic lymphocytic leukemic cells.
Chemotherapy resistance remains a major clinical problem in patients with B-cell chronic lymphocytic leukemia (B-CLL). Proteasome inhibitors are able to induce apoptosis in chemotherapy-resistant B-CLL cells in vitro. Exposure of B-CLL cells to the proteasome inhibitors, MG132 and lactacystin, resulted in inhibition of proteasomal activity within 30 min of treatment and was accompanied by an increase in the level of ubiquitinated proteins. Proteasome inhibitors did not alter the levels of expression of the proapoptotic Bcl-2 family proteins, Bax and Bid, prior to the onset of apoptosis. Instead, proteasome inhibitors induced a caspase-independent conformational change in Bax (as shown by a conformation-specific Bax antibody) and its translocation to mitochondria, resulting in mitochondrial perturbation, as evidenced by loss of the mitochondrial membrane potential and cytochrome c release. Similar conformational change and subcellular localization of Bax were observed during apoptosis induced with fludarabine, chlorambucil and prednisolone. These data suggest that alteration of Bax conformation and its redistribution to mitochondria are common and early features of B-CLL apoptosis in response to proteasome inhibitors and other chemotherapeutic agents.
MRC Toxicology Unit, Hodgkin Building, University of Leicester, PO Box 138, Lancaster Road, Leicester LE1 9HN, UK.
Grant
G
Dewson
Roger T
RT
Snowden
Jason B
JB
Almond
Martin J S
MJ
Dyer
Gerald M
GM
Cohen
D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism; D003546:Cysteine Endopeptidases; D003574:Cytochrome c Group / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D021381:Protein Transport / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D025801:Ubiquitin / Q000378:metabolism; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D003574:Cytochrome c Group; D009097:Multienzyme Complexes; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D025801:Ubiquitin; D051028:bcl-2-Associated X Protein; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex