ABSTRACT
OBJECTIVE TNF- related apoptosis- inducing ligand(TRAIL)is a promising cancer therapeutic agent due to its minimal toxicity to normal tissues and remarkable apoptotic activity in tumors. However, most breast cancer cells are resistant to TRAIL- induced apoptosis. Our objectives are to investigate the underlying molecular mechanisms and to develop strategies to overcome such resistance. METHODS To identify modulators of TRAIL-induced apoptosis, we carried out a genome wide siRNA screen. To validate the screening result, we either silenced or overexpressed the identified genes in various breast cancer cells and changes in growth and TRAIL-induced cell apoptosis were determined in vitro and in an orthotopic xenograft mouse model. Finally, we investigated whether small molecules targeting the identified genes improve the effectiveness of TRAIL-therapy. RESULTS We unexpectedly identified androgen receptor (AR) to be responsible for TRAIL resistance. While AR is classically viewed as the key factor in prostate cancer progression, we found that AR expression levels were markedly elevated in human invasive breast cancer specimens including triple- negative breast cancers (TNBC) that are highly aggressive with poor prognosis. Importantly, breast cancer cell lines express different levels of AR that correlated with their TRAIL resistance. AR overexpression in MDA- MB- 231 and MDA- MB- 436 cells suppressed the TRAIL sensitivity whereas knockdown of AR rendered MCF-7 and MDA-MB-453 cells sensitive to TRAIL-induced apoptosis. AR overexpression also induced TRAIL resistance in breast tumors in vivo. Further, we observed an upregulation of the TRAIL receptor, death receptor 5 (DR5) in breast cancer cells, following the removal or inhibition of AR by its antagonists Casodex and MDV3100. Treatment with AR antagonists also enhanced TRAIL- induced breast cancer cell apoptosis. CONCLUSION AR signaling suppresses TRAIL-induced breast cancer cell apoptosis, in part, by suppressing DR5 expression, and a combination of AR antagonists together with TRAIL may be a novel and effective therapy for TNBC.
ABSTRACT
OBJECTIVE The objective of this study was to characterize the neurotransmitter systems that cause constriction of murine airways. METHODS Murine precision cut lung slices (PCLS) and trachea were prepared, placed into perfusion chambers equipped with platinum electrodes and stimulated transmurally (1.0 ms, 50 V, 0.1- 30 Hz). To measure PCLS constriction, changes in airway luminal area in response to electric field stimulation (EFS) were captured as video images quantified using Image J software. For trachea, changes in isometric tension were recorded using Grass force transducers. Frequency response curves were generated in the absence and the presence of the inhibitors magnesium, atropine and capsaicin and responses analyzed and compared using a student' s t- test (P<0.05). RESULTS EFS caused airway constriction in a frequency-dependent manner that was best fit by a biphasic curve. Neuron-specific stimulation was verified by Mg2+ blockade. Maximum airway constriction to 30 Hz EFS in PCLS was (51.8±3.0)% while tracheal constriction averaged (551±80)mg. Interestingly, in PCLS the muscarinic receptor antagonist atropine (10 μmol · L- 1) blocked (99.5 ± 7.2)% of EFS induced constriction at 1 Hz, but only blocked (23.3±3.8)% of EFS induced constriction at 30 Hz and eliminated the first phase but not the second phase of the biphasic EFS response. Treatment with capsaicin to deplete sensory neurotransmitters significantly increased EFS constriction supporting the presence of sensory neurotransmitter systems in airways. CONCLUSION These data are consistent with parasympathetic constriction of airways by acetylcholine at lower EFS frequencies while higher frequencies release sensory dilator neurotransmitters. These data provide evidence for multiple nerve types innervating airways which may provide novel targets for treatment of lung disease.