By. Li et Qp. Dou, Bax degradation by the ubiquitin/proteasome-dependent pathway: involvementin tumor survival and progression, P NAS US, 97(8), 2000, pp. 3850-3855
Citations number
31
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Previously we reported that proteasome inhibitors were able to overcome Bcl
-2-mediated protection from apoptosis. Here we show that inhibition of the
proteasome activity in Bcl-2-overexpressing cells accumulates the proapopto
tic Bar protein to mitochondria/cytoplasm, where it interacts to Bcl-2 prot
ein. This event was followed by release of mitochondrial cytochrome c into
the cytosol and activation of caspase-mediated apoptosis. In contrast, prot
easome inhibition did not induce any apparent changes in Bcl-2 protein leve
ls. In addition, treatment with a proteasome inhibitor increased levels of
ubiquitinated forms of Bar protein, without any effects on Bar mRNA express
ion. We also established a cell-free Bar degradation assay in which an in v
itro-translated, S-35-labeled Bar protein can be degraded by a tumor cell p
rotein extract, inhibitable by addition of a proteasome inhibitor or deplet
ion of the proteasome or ATP, The Bar degradation activity can be reconstit
uted in the proteasome-depleted supernatant by addition of a purified 20S p
roteasome or proteasome-enriched fraction. Finally, by using tissue samples
of human prostate adenocarcinoma, we demonstrated that increased levels of
Bar degradation correlated well with decreased levels of Bar protein and i
ncreased Gleason scores of prostate cancer. Our studies strongly suggest th
at ubiquitin/proteasome-mediated Bar degradation is a novel survival mechan
ism in human cancer cells and that selective targeting of this pathway shou
ld provide a unique approach for treatment of human cancers, especially tho
se overexpressing Bcl-2.