The mitochondrial ATP-dependent Lon protease: a novel target in lymphoma death mediated by the synthetic triterpenoid CDDO and its derivatives.
Synthetic triterpenoids are multitarget compounds exhibiting promise as preventative and therapeutic agents for cancer. Their proposed mechanism of action is by forming Michael adducts with reactive nucleophilic groups on target proteins. Our previous work demonstrates that the 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and its derivatives promote B-lymphoid cell apoptosis through a mitochondria-mediated pathway linked to mitochondrial protein aggregation. As one function of the Lon protease is to eliminate abnormal mitochondrial proteins, we hypothesized that CDDO-induced protein aggregation and lymphoma apoptosis occur by inactivating this enzyme. Here, we show that CDDO and its derivatives directly and selectively inhibit Lon. CDDO blocks Lon-mediated proteolysis in biochemical and cellular assays, but does not inhibit the 20S proteasome. Furthermore, a biotinylated-CDDO conjugate modifies mitochondrial Lon. A striking common phenotype of CDDO-treated lymphoma cells and Lon-knockdown cells is the accumulation of electron-dense aggregates within mitochondria. We also show that Lon protein levels are substantially elevated in malignant lymphoma cells, compared with resting or activated B cells. Finally, we demonstrate that Lon knockdown leads to lymphoma cell death. Together, these findings suggest that Lon inhibition plays a contributory role in CDDO-induced lymphoma cell death, and support the concept that mitochondrial Lon is a novel anticancer drug target.
James P. Wilmot Cancer Center, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642, USA. steven_bernstein@urmc.rochester.edu
Steven H
SH
Bernstein
Sundararajan
S
Venkatesh
Min
M
Li
Jae
J
Lee
Bin
B
Lu
Shannon P
SP
Hilchey
Kimberly M
KM
Morse
Hollie M
HM
Metcalfe
Jolanta
J
Skalska
Michael
M
Andreeff
Paul S
PS
Brookes
Carolyn K
CK
Suzuki
D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D055785:Gene Knockdown Techniques; D006801:Humans; D002479:Inclusion Bodies / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008223:Lymphoma / Q000201:enzymology* / Q000235:genetics; D016393:Lymphoma, B-Cell / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D009828:Oleanolic Acid / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D049070:Protease La / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects; D011485:Protein Binding; D015854:Up-Regulation
C116817:2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid; D009828:Oleanolic Acid; D049070:Protease La; D046988:Proteasome Endopeptidase Complex