Oxidative stress sensitizes bladder cancer cells to TRAIL mediated apoptosis by down-regulating anti-apoptotic proteins.
OBJECTIVE
TRAIL, an endogenous protein involved in immunosurveillance and a novel drug in clinical trials, is of particular interest as cancer therapy because it can induce apoptosis in cancer cells but not in normal cells. Since some cancers develop resistance to TRAIL, safe and effective methods of TRAIL sensitization are of clinical interest. We explored how chemotherapy and oxidative stress affect TRAIL sensitivity and expression of proteins in the apoptotic pathway.


METHODS
Sensitivity to TRAIL was assessed in viability assays. Apoptosis was measured by caspase-3/7 activity and/or nuclear condensation using Hoechst staining. Western blotting was used to determine cleavage, phosphorylation or alterations in protein expression.


RESULTS
TRAIL decreased the viability of 5637 but not of J82 or T24 bladder carcinoma cells (ATCC(R)). Chemotherapy with doxorubicin or cisplatin (Ben Venue Laboratories, Bedford, Ohio) decreased the expression of the anti-apoptotic protein cFLIP(S) and increased caspase-8 cleavage, reversing TRAIL resistance in T24 cells. Specific targeting of cFLIP(S) by siRNA was insufficient for sensitization to TRAIL in T24 cells. However, chemotherapy mediated TRAIL sensitization was mimicked by low concentrations of H(2)O(2), which resulted in the phosphorylation of translation EF2 and decreased the expression of several short half-life, anti-apoptotic proteins, including FLIP(S), XIAP and survivin.


CONCLUSIONS
Inducing oxidative stress by low H(2)O(2) concentrations may reverse TRAIL resistance. This warrants the further exploration of H(2)O(2) as an adjuvant intravesical treatment to lower the apoptotic threshold of bladder cancer cells.
White-Gilbertson
Shai J
SJ
Department of Microbiology and Immunology, Medical University of South Carolina, Charleston, South Carolina 29403, USA.
Kasman
Laura
L
McKillop
John
J
Tirodkar
Tejas
T
Lu
Ping
P
Voelkel-Johnson
Christina
C
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000502:physiology; D045744:Cell Line, Tumor; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D006801:Humans; D018384:Oxidative Stress / Q000502:physiology*; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000502:physiology*; D001749:Urinary Bladder Neoplasms / Q000503:physiopathology*
D000970:Antineoplastic Agents; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053221:TNF-Related Apoptosis-Inducing Ligand