Proteasome proteolytic profile is linked to Bcr-Abl expression.
OBJECTIVE
We have previously demonstrated that proteasome activity is higher in bone marrow from patients with chronic myeloid leukemia (CML) than normal controls. This study investigates whether there is any relationship between Bcr-Abl expression and proteasome activity.


METHODS
Fluorogenic substrate assays and an activity-based probe were used to profile proteasome activity in CML cell-line models and the effect of the proteasome inhibitor BzLLLCOCHO on these cell-line models and primary CML cells was investigated.


RESULTS
We have demonstrated that oncogenic transformation by BCR-ABL is associated with an increase in proteasome proteolytic activity. Furthermore, small interfering RNA targeted against BCR-ABL reduces proteasome activity. In addition, we have found that Bcr-Abl-positive cells are more sensitive than Bcr-Abl-negative cells to induction of apoptosis by the proteasome inhibitor BzLLLCOCHO, and that sequential addition of imatinib followed by BzLLLCOCHO has an additive effect on the induction of apoptosis in Bcr-Abl-positive cells. Finally, we demonstrate that cell lines that become resistant to imatinib remain sensitive to proteasome inhibition.


CONCLUSIONS
This is the first time that a direct relationship has been demonstrated between BCR-ABL transformation and the enzymatic activity of the proteasome. Our results suggest that the proteasome might provide a useful therapeutic target in CML, particularly in those patients who have developed resistance to conventional treatment.
Crawford
Lisa J
LJ
Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, UK.
Windrum
Phlip
P
Magill
Laura
L
Melo
Junia V
JV
McCallum
Lynn
L
McMullin
Mary F
MF
Ovaa
Huib
H
Walker
Brian
B
Irvine
Alexandra E
AE
D017209:Apoptosis; D001549:Benzamides; D002471:Cell Transformation, Neoplastic; D019008:Drug Resistance, Neoplasm; D016044:Fusion Proteins, bcr-abl / Q000032:analysis*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000068877:Imatinib Mesylate; D020014:K562 Cells; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000473:pathology*; D010879:Piperazines / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D001549:Benzamides; D010879:Piperazines; D011480:Protease Inhibitors; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl; D046988:Proteasome Endopeptidase Complex