Effects of thymoquinone on isolated and cellular proteasomes.
Thymoquinone, a naturally derived agent, has been shown to possess antioxidant, antiproliferative and proapoptotic activities. In the present study, we explored thymoquinone effects on the proteasomal complex, the major system involved in the removal of damaged, oxidized and misfolded proteins. In purified 20S complexes, subunit-dependent and composition-dependent inhibition was observed, and the chymotrypsin-like and trypsin-like activities were the most susceptible to thymoquinone treatment. U87 MG and T98G malignant glioma cells were treated with thymoquinone, and 20S and 26S proteasome activity was measured. Inhibition of the complex was evident in both cell lines, but predominantly in U87 MG cells, and was accompanied by accumulation of ubiquitin conjugates. Accumulation of p53 and Bax, two proteasome substrates with proapoptotic activity, was observed in both cell lines. Our results demonstrate that thymoquinone induces selective and time-dependent proteasome inhibition, both in isolated enzymes and in glioblastoma cells, and suggest that this mechanism could be implicated in the induction of apoptosis in cancer cells.
Cecarini
Valentina
V
University of Camerino, Italy. valentina.cecarini@unicam.it <valentina.cecarini@unicam.it>
Quassinti
Luana
L
Di Blasio
Alessia
A
Bonfili
Laura
L
Bramucci
Massimo
M
Lupidi
Giulio
G
Cuccioloni
Massimiliano
M
Mozzicafreddo
Matteo
M
Angeletti
Mauro
M
Eleuteri
Anna Maria
AM
D016227:Benzoquinones / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005909:Glioblastoma / Q000378:metabolism / Q000473:pathology; D006801:Humans; D015394:Molecular Structure; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000302:isolation & purification / Q000378:metabolism; D061988:Proteasome Inhibitors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
C494826:BAX protein, human; D016227:Benzoquinones; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D046988:Proteasome Endopeptidase Complex; C003466:thymoquinone