Dissecting the roles of DR4, DR5 and c-FLIP in the regulation of geranylgeranyltransferase I inhibition-mediated augmentation of TRAIL-induced apoptosis.
BACKGROUND
Geranylgeranyltransferase I (GGTase I) has emerged as a cancer therapeutic target. Accordingly, small molecules that inhibit GGTase I have been developed and exhibit encouraging anticancer activity in preclinical studies. However, their underlying anticancer mechanisms remain unclear. Here we have demonstrated a novel mechanism by which GGTase I inhibition modulates apoptosis.


RESULTS
The GGTase I inhibitor GGTI-298 induced apoptosis and augmented tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human lung cancer cells. GGTI-298 induced DR4 and DR5 expression and reduced c-FLIP levels. Enforced c-FLIP expression or DR5 knockdown attenuated apoptosis induced by GGTI-298 and TRAIL combination. Surprisingly, DR4 knockdown sensitized cancer cells to GGTI298/TRAIL-induced apoptosis. The combination of GGTI-298 and TRAIL was more effective than each single agent in decreasing the levels of IkappaBalpha and p-Akt, implying that GGTI298/TRAIL activates NF-kappaB and inhibits Akt. Interestingly, knockdown of DR5, but not DR4, prevented GGTI298/TRAIL-induced IkappaBalpha and p-Akt reduction, suggesting that DR5 mediates reduction of IkappaBalpha and p-Akt induced by GGTI298/TRAIL. In contrast, DR4 knockdown further facilitated GGTI298/TRAIL-induced p-Akt reduction.


CONCLUSIONS
Both DR5 induction and c-FLIP downregulation contribute to GGTI-298-mediated augmentation of TRAIL-induced apoptosis. Moreover, DR4 appears to play an opposite role to DR5 in regulation of GGTI/TRAIL-induced apoptotic signaling.
Chen
Shuzhen
S
Department of Hematology and Medical Oncology, Emory University School of Medicine and Winship Cancer Institute, Atlanta, Georgia, USA.
Fu
Lei
L
Raja
Shruti M
SM
Yue
Ping
P
Khuri
Fadlo R
FR
Sun
Shi-Yong
SY
D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors*; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides / Q000494:pharmacology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism*; D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D008175:Lung Neoplasms / Q000201:enzymology / Q000473:pathology; D000072000:NF-KappaB Inhibitor alpha; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects; D020743:rhoB GTP-Binding Protein / Q000378:metabolism
D001549:Benzamides; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; C102521:GGTI 298; C530102:GGTI-DU40; D020672:I-kappa B Proteins; C000606204:NFKBIA protein, human; D011720:Pyrazoles; D011725:Pyridines; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; D000072000:NF-KappaB Inhibitor alpha; D019883:Alkyl and Aryl Transferases; C083291:geranylgeranyltransferase type-I; D051057:Proto-Oncogene Proteins c-akt; D020743:rhoB GTP-Binding Protein