Premium
Proteasome inhibition blocks caspase‐8 degradation and sensitizes prostate cancer cells to death receptor‐mediated apoptosis
Author(s) -
Thorpe Jeffery A.,
Christian Perry A.,
Schwarze Steven R.
Publication year - 2007
Publication title -
the prostate
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.295
H-Index - 123
eISSN - 1097-0045
pISSN - 0270-4137
DOI - 10.1002/pros.20706
Subject(s) - fas ligand , apoptosis , caspase 8 , proteasome , programmed cell death , cancer research , proteasome inhibitor , prostate cancer , caspase , annexin , cancer cell , cancer , medicine , caspase 3 , biology , microbiology and biotechnology , biochemistry
BACKGROUND Proteasome inhibition through the administration of Velcade is a viable chemotherapeutic strategy that is approved to treat multiple myeloma and is being evaluated for efficacy against prostate cancer. Currently, the apoptotic pathways that contribute to this anticancer response are poorly understood. Our goal is to test the extent to which proteasome inhibition modulates apoptosis through death receptor pathways. METHODS Several prostate cancer cell lines and primary prostate epithelial cells (PrECs) were used as models. The death receptor pathway was activated by the expression of Fas ligand (FasL) or addition of TNF‐related apoptosis‐inducing ligand (TRAIL) in the presence or absence of proteasome inhibitors. The apoptotic response was quantified by annexin V, TUNEL and nuclear condensation assays. Western blot analysis was conducted to quantify protein levels and enzyme assays were used to measure caspase activity. RESULTS Proteasome inhibition markedly sensitized prostate cancer cells to apoptosis initiated by Fas ligand (FasL) or TRAIL. In the presence of either death ligand, procaspase‐8 processing occurred, but led to minimal amounts of active caspase‐8. The addition of Velcade, however, led to robust active caspase‐8 protein abundance and activity. In the presence of Velcade the caspase‐8 p18 subunit half‐life increased from 22 min to over 2 hr. CONCLUSIONS These findings demonstrate that proteasome inhibition can sensitize cells to apoptosis elicited by tumor necrosis factor ligands and retarding caspase‐8 degradation provides one explanation for this activity. This study suggests that the clinical efficacy of Velcade may result, at least in part, from the activity of death ligands. Prostate 68: 200–209, 2008. © 2007 Wiley‐Liss, Inc.