Inhibition of proteasomal degradation of Mcl-1 by cobalt chloride suppresses cobalt chloride-induced apoptosis in HCT116 colorectal cancer cells.
Cobalt promotes apoptosis in multiple cell systems, however, the molecular mechanisms that influence cobalt-induced apoptosis are not fully understood. We investigated mechanisms of cobalt chloride induced apoptosis in HCT116 colorectal cancer cells. Cobalt chloride induced dose dependent apoptosis in HCT116 cells (250-750 muM) which, at higher concentrations (500-750 muM), was associated with an increase in the expression of the Bcl-2-related Mcl-1 survival protein. Cobalt chloride caused the accumulation of higher molecular weight ubiquitin-conjugates of Mcl-1 in intact HCT116 cells and inhibited the activity of the trypsin-like site of the 20S proteasome in an in vitro assay. Although siRNA-mediated knockdown of Mcl-1 increased apoptosis in HCT116 cells, the combination of Mcl-1 siRNA and cobalt chloride induced very high levels of cell killing. Therefore, inhibition of the proteasome by cobalt chloride leads to the accumulation of Mcl-1 which acts to limit cobalt chloride induced apoptosis.
Lee
Melanie
M
Cancer Research UK Clinical Centre, Cancer Sciences Division, University of Southampton School of Medicine, Southampton General Hospital, Southampton, SO16 6YD, UK.
Lapham
Abigail
A
Brimmell
Matthew
M
Wilkinson
Helen
H
Packham
Graham
G
D016587:Antimutagenic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000187:drug effects / Q000378:metabolism; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D002277:Carcinoma / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D003035:Cobalt / Q000494:pharmacology*; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D025461:Feedback, Physiological / Q000187:drug effects / Q000235:genetics; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference / Q000502:physiology; D034741:RNA, Small Interfering; D054875:Ubiquitination / Q000187:drug effects / Q000502:physiology
D016587:Antimutagenic Agents; D051017:Apoptosis Regulatory Proteins; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D003035:Cobalt; D046988:Proteasome Endopeptidase Complex; C018021:cobaltous chloride