title: Resistance to Fas-mediated apoptosis is restored by cycloheximide through the downregulation of cellular FLIPL in NK/T-cell lymphoma.
abstract: Extranodal NK/T-cell lymphoma (NKTL), nasal type, is a highly aggressive neoplasm and is strongly associated with Epstein-Barr virus (EBV). In this study, we demonstrate that EBV-positive NKTL cell lines, namely, Hank-1, NK-YS, and NK-L, are resistant to Fas-mediated apoptosis induced by anti-Fas antibodies despite high levels of Fas surface expression and no mutation in the Fas gene. Fas stimulation of Hank-1 and NK-YS cells showed little processing of caspase 8, caspase 3, or bid, although the proximal signaling molecules of the death-inducing signaling complex, namely, Fas, Fas-associated protein with a death domain, caspase 8, and bid were present in these cells. Consistent with previous reports on the hypermethylation of death associated protein (DAP) kinase in NKTLs, the promoter of DAP kinase was methylated and its mRNA not detected in Hank-1 cells. However, the restoration of DAP kinase expression by 5-aza-2'-deoxycytidine did not sensitize Hank-1 to Fas-mediated apoptosis, indicating that DAP kinase deficiency does not contribute to resistance to Fas-mediated apoptosis. Since etoposide-induced apoptosis involved caspase 3 activation in Hank-1 and NK-YS cells, the caspase 3-dependent apoptotic machinery appears to be intact. Interestingly, cotreatment of Hank-1 with cycloheximide, a protein synthesis inhibitor, markedly sensitized cells to Fas-mediated apoptosis along with caspase 8 activation and c-FLIP(L) (cellular FLICE inhibitory protein long form) downregulation. Moreover, immunohistochemistry on paraffin-embedded tissue revealed c-FLIP expression in 39% (14 of 36) of NKTL patients. Taken together, these findings indicate that c-FLIP(L)-mediated resistance to Fas contributes to the development and progression of NKTLs. This study also suggests that agents capable of downregulating c-FLIP(L) could be used to treat NKTL.
authors.affiliation: Department of Pathology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Yoon Kyung
authors.initials: YK
authors.lastname: Jeon
authors.forename: Heejung
authors.initials: H
authors.lastname: Kim
authors.forename: Soo Oh
authors.initials: SO
authors.lastname: Park
authors.forename: Hye Young
authors.initials: HY
authors.lastname: Choi
authors.forename: Young A
authors.initials: YA
authors.lastname: Kim
authors.forename: Sung-Shin
authors.initials: SS
authors.lastname: Park
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Kim
authors.forename: Yong Nyun
authors.initials: YN
authors.lastname: Kim
authors.forename: Chul-Woo
authors.initials: CW
authors.lastname: Kim
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D020169:Caspases / Q000096:biosynthesis; D049109:Cell Proliferation; D002470:Cell Survival; D003513:Cycloheximide / Q000494:pharmacology*; D064550:Death-Associated Protein Kinases; D000077209:Decitabine; D015536:Down-Regulation; D004789:Enzyme Activation; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019169:Jurkat Cells / Q000187:drug effects / Q000473:pathology; D007694:Killer Cells, Natural; D016411:Lymphoma, T-Cell, Peripheral / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*; D019014:fas Receptor / Q000096:biosynthesis* / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D047908:Intracellular Signaling Peptides and Proteins; D011500:Protein Synthesis Inhibitors; D019014:fas Receptor; D005047:Etoposide; D000077209:Decitabine; D003513:Cycloheximide; D064550:Death-Associated Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020169:Caspases; D001374:Azacitidine