An L-tyrosine derivative and PPARgamma agonist, GW7845, activates a multifaceted caspase cascade in bone marrow B cells.
Apoptosis is a critical event in the deletion of B lymphocytes prior to their migration to the periphery. Synthetic peroxisome proliferator activated receptor gamma (PPARgamma) agonists, including the drug GW7845 and the environmental contaminant mono-(2-ethylhexyl) phthalate, as well as an endogenous ligand, 15-deoxy-Delta(12,14)-prostaglandin J(2), induce clonally unrestricted apoptosis in pro/pre-B cells. Considering that PPARgamma agonists are used clinically for the treatment of diabetes and postulated to be useful as chemotherapeutics, we used GW7845 as a model PPARgamma agonist to examine the mechanism of cell death that may contribute to tumor killing as well as normal bone marrow B lymphocyte toxicity. GW7845 induced rapid mitochondrial membrane depolarization and release of cytochrome c, along with nearly concurrent activation of capases-2, -3, -8, and -9 in primary pro-B cells and BU-11 cells, a nontransformed pro/pre-B cell line. GW7845-induced apoptosis was reduced significantly in Bax-deficient and Apaf-1 mutant primary pro-B cells, supporting the conclusion that GW7845-induced apoptosis is mitochondria- and apoptosome-dependent. Using benzyloxycarbonyl-VAD-fluoromethyl ketone (VAD-FMK) as a pan-caspase inhibitor, we demonstrated that an initial cytochrome c release occurred independently of caspase activation and that only caspase-9 activation was partially caspase independent. The attenuation of GW7845-induced apoptosis by multiple FMK-labeled peptide sequences suggests that multiple caspase pathways are responsible for initiating and executing apoptosis. The strong activation of Bid provides a mechanism by which caspases-2, -3, and -8 may amplify the apoptotic signal. These data support the hypothesis that pharmacologic concentrations of PPARgamma agonists induce an intrinsic apoptotic pathway that is driven in normal bone marrow B cells by multiple amplification loops.
Schlezinger
Jennifer J
JJ
Department of Environmental Health, Boston University School of Public Health, Boston, Massachusetts 02118, USA. jschlezi@bu.edu
Emberley
Jessica K
JK
Bissonnette
Stephanie L
SL
Sherr
David H
DH
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001854:Bone Marrow Cells / Q000187:drug effects / Q000201:enzymology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D015151:Immunoblotting; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D051336:Mitochondrial Membranes / Q000187:drug effects; D010080:Oxazoles / Q000494:pharmacology*; D047495:PPAR gamma / Q000819:agonists*; D015398:Signal Transduction / Q000187:drug effects; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000494:pharmacology*
D061945:Caspase Inhibitors; D010080:Oxazoles; D047495:PPAR gamma; C401311:GW 7845; D014443:Tyrosine; D045304:Cytochromes c; D020169:Caspases