The natural product honokiol preferentially inhibits cellular FLICE-inhibitory protein and augments death receptor-induced apoptosis.
Targeting death receptor-mediated apoptosis has emerged as an effective strategy for cancer therapy. However, certain types of cancer cells are intrinsically resistant to death receptor-mediated apoptosis. In an effort to identify agents that can sensitize cancer cells to death receptor-induced apoptosis, we have identified honokiol, a natural product with anticancer activity, as shown in various preclinical studies, as an effective sensitizer of death receptor-mediated apoptosis. Honokiol alone moderately inhibited the growth of human lung cancer cells; however, when combined with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), greater effects on decreasing cell survival and inducing apoptosis than TRAIL alone were observed, indicating that honokiol cooperates with TRAIL to enhance apoptosis. This was also true to Fas-induced apoptosis when combined with Fas ligand or an agonistic anti-Fas antibody. Among several apoptosis-associated proteins tested, cellular FLICE-inhibitory protein (c-FLIP) was the only one that was rapidly down-regulated by honokiol in all of the tested cell lines. The down-regulation of c-FLIP by honokiol could be prevented by the proteasome inhibitor MG132. Moreover, honokiol increased c-FLIP ubiquitination. These results indicate that honokiol down-regulates c-FLIP by facilitating its degradation through a ubiquitin/proteasome-mediated mechanism. Enforced expression of ectopic c-FLIP abolished the ability of honokiol to enhance TRAIL-induced apoptosis. Several honokiol derivatives, which exhibited more potent effects on down-regulation of c-FLIP than honokiol, showed better efficacy than honokiol in inhibiting the growth and enhancing TRAIL-induced apoptosis as well. Collectively, we conclude that c-FLIP down-regulation is a key event for honokiol to modulate the death receptor-induced apoptosis.
Raja
Shruti M
SM
Department of Hematology and Medical Oncology, Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Chen
Shuzhen
S
Yue
Ping
P
Acker
Timothy M
TM
Lefkove
Benjamin
B
Arbiser
Jack L
JL
Khuri
Fadlo R
FR
Sun
Shi-Yong
SY
D017209:Apoptosis / Q000187:drug effects*; D001713:Biphenyl Compounds / Q000737:chemistry / Q000494:pharmacology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000037:antagonists & inhibitors*; D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D017705:Lignans / Q000737:chemistry / Q000494:pharmacology*; D008175:Lung Neoplasms / Q000201:enzymology / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D053218:Receptors, Death Domain / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology; D025801:Ubiquitin / Q000378:metabolism; D000498:Allyl Compounds; D010636:Phenols
D001713:Biphenyl Compounds; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D048031:JNK Mitogen-Activated Protein Kinases; D017705:Lignans; D046988:Proteasome Endopeptidase Complex; D053218:Receptors, Death Domain; D053221:TNF-Related Apoptosis-Inducing Ligand; D025801:Ubiquitin; C005499:honokiol; D000498:Allyl Compounds; D010636:Phenols