title: Histone deacetylase inhibitors sensitize glioblastoma cells to TRAIL-induced apoptosis by c-myc-mediated downregulation of cFLIP.
abstract: Glioblastoma is the most common primary brain tumor with a very poor prognosis, calling for novel treatment strategies. Here, we provide first evidence that histone deacetylase inhibitors (HDACI) prime glioblastoma cells for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) -induced apoptosis at least in part by c-myc-mediated downregulation of cellular FLICE-inhibitory protein (cFLIP). Pretreatment with distinct HDACI (MS275, suberoylanilide hydroxamic acid, valproic acid) significantly enhances TRAIL-induced apoptosis in several glioblastoma cell lines. Monitoring a panel of apoptosis-regulatory proteins revealed that MS275 reduces the expression of cFLIP(L) and cFLIP(S). This leads to decreased recruitment of cFLIP(L) and cFLIP(S) and increased activation of caspase-8 to the TRAIL death-inducing signaling complex, resulting in enhanced cleavage of caspase-8, -9 and -3 and caspase-dependent apoptosis. Also, MS275 promotes TRAIL-triggered processing of Bid, activation of Bax, loss of mitochondrial membrane potential and release of cytochrome c. MS275-mediated downregulation of cFLIP occurs at the mRNA level independent of proteasome- or caspase-mediated degradation, and is preceded by upregulation of nuclear levels of c-myc, a transcriptional repressor of cFLIP. Notably, MS275 causes increased binding of c-myc to the cFLIP promoter and reduces cFLIP promoter activity. Indeed, knockdown of c-myc partially rescues cFLIP(L) from MS275-inferred downregulation and significantly decreases TRAIL- and MS275-induced apoptosis. Also, overexpression of cFLIP(L) or cFLIP(S) significantly reduces MS275- and TRAIL-induced apoptosis. Importantly, MS275 sensitizes primary cultured glioblastoma cells towards TRAIL and cooperates with TRAIL to reduce long-term clonogenic survival of glioblastoma cells and to suppress glioblastoma growth in vivo underscoring the clinical relevance of this approach. Thus, these findings demonstrate that HDACI represent a promising strategy to prime glioblastoma for TRAIL-induced apoptosis by targeting cFLIP.
authors.affiliation: University Children's Hospital, Ulm, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Bangert
authors.forename: S
authors.initials: S
authors.lastname: Cristofanon
authors.forename: I
authors.initials: I
authors.lastname: Eckhardt
authors.forename: B A
authors.initials: BA
authors.lastname: Abhari
authors.forename: S
authors.initials: S
authors.lastname: Kolodziej
authors.forename: S
authors.initials: S
authors.lastname: Häcker
authors.forename: S H K
authors.initials: SH
authors.lastname: Vellanki
authors.forename: J
authors.initials: J
authors.lastname: Lausen
authors.forename: K-M
authors.initials: KM
authors.lastname: Debatin
authors.forename: S
authors.initials: S
authors.lastname: Fulda
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics* / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002463:Cell Membrane Permeability / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005909:Glioblastoma / Q000235:genetics* / Q000378:metabolism*; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D053218:Receptors, Death Domain / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D056572:Histone Deacetylase Inhibitors; D016271:Proto-Oncogene Proteins c-myc; D053218:Receptors, Death Domain; D053221:TNF-Related Apoptosis-Inducing Ligand; D020169:Caspases