Structurally diverse peroxisome proliferator-activated receptor agonists induce apoptosis in human uro-epithelial cells by a receptor-independent mechanism involving store-operated calcium channels.
OBJECTIVE
Peroxisome proliferator-activated receptors (PPARs) are implicated in epithelial cell proliferation and differentiation, but investigation has been confounded by potential off-target effects of some synthetic PPAR ligands. Our aim was to determine mechanisms underlying the pro-apoptotic effect of synthetic PPAR agonists in normal human bladder uro-epithelial (urothelial) cells and to reconcile this with the role of PPARs in urothelial cytodifferentiation.


METHODS
Normal human urothelial (NHU) cells were grown as non-immortal lines in vitro and exposed to structurally diverse agonists ciglitazone, troglitazone, rosiglitazone (PPARgamma), ragaglitazar (PPARalpha/gamma), fenofibrate (PPARalpha) and L165041 (PPARbeta/delta).


RESULTS
NHU cells underwent apoptosis following acute exposure to ciglitazone, troglitazone or ragaglitazar, but not fenofibrate, L165041 or rosiglitazone, and this was independent of ERK or p38 MAP-kinase activation. Pro-apoptotic agonists induced sustained increases in intracellular calcium, whereas removal of extracellular calcium altered the kinetics of ciglitazone-mediated calcium release from sustained to transient. Cell death was accompanied by plasma-membrane disruption, loss of mitochondrial membrane-potential and caspase-9/caspase-3 activation. PPARgamma-mediated apoptosis was unaffected following pre-treatment with PPARgamma antagonist T0070907 and was strongly attenuated by store-operated calcium channel (SOC) inhibitors 2-APB and SKF-96365.


CONCLUSIONS
Our results provide a mechanistic basis for the ability of some PPAR agonists to induce death in NHU cells and demonstrate that apoptosis is mediated via PPAR-independent mechanisms, involving intracellular calcium changes, activation of SOCs and induction of the mitochondrial apoptotic pathway.
Chopra
B
B
Department of Biology, Jack Birch Unit of Molecular Carcinogenesis, University of York, York, UK.
Georgopoulos
N T
NT
Nicholl
A
A
Hinley
J
J
Oleksiewicz
M B
MB
Southgate
J
J
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002839:Chromans / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D011345:Fenofibrate / Q000494:pharmacology; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D000960:Hypolipidemic Agents / Q000494:pharmacology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D010078:Oxazines / Q000494:pharmacology; D047492:Peroxisome Proliferator-Activated Receptors / Q000819:agonists* / Q000378:metabolism; D010642:Phenoxyacetates / Q000494:pharmacology; D010666:Phenylpropionates / Q000494:pharmacology; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000494:pharmacology; D000077288:Troglitazone; D019459:Urothelium / Q000166:cytology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C520164:4-(3-(2-propyl-3-hydroxy-4-acetyl)phenoxy)propyloxyphenoxy acetic acid; D015220:Calcium Channels; D002839:Chromans; D007004:Hypoglycemic Agents; D000960:Hypolipidemic Agents; D010078:Oxazines; D047492:Peroxisome Proliferator-Activated Receptors; D010642:Phenoxyacetates; D010666:Phenylpropionates; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D000077288:Troglitazone; C432703:ragaglitazar; D002118:Calcium; D011345:Fenofibrate; C039671:ciglitazone