title: Inhibition of SREBP1 sensitizes cells to death ligands.
abstract: Evasion of death receptor ligand-induced apoptosis contributs to cancer development and progression. To better understand mechanisms conferring resistance to death ligands, we screened an siRNA library to identify sequences that sensitize resistant cells to fas activating antibody (CH-11). From this screen, we identified the Sterol-Regulatory Element-Binding Protein 1 (SREBP1), a transcription factor, which regulates genes involved in cholesterol and fatty acid synthesis including fatty acid synthase. Inhibition of SREBP1 sensitized PPC-1 and HeLa to the death receptor ligands CH-11 and TRAIL. In contrast, DU145 prostate cancer cells that are resistant to death ligands despite expressing the receptors on their cell surface remained resistant to CH-11 and TRAIL after knockdown of SREBP1. Consistent with the effects on cell viability, the addition of CH-11 activated caspases 3 and 8 in HeLa but not DU145 cells with silenced SREBP1. We demonstrated that knockdown of SREBP1 produced a marked decrease in fatty acid synthase expression. Furthermore, genetic or chemical inhibition of fatty acid synthase with shRNA or orlistat, respectively, recapitulated the effects of SREBP1 inhibition and sensitized HeLa but not DU145 cells to CH-11 and TRAIL. Sensitization to death receptor ligands by inhibition of fatty acid synthase was associated with activation of caspase 8 prior to caspase 9. Neither silencing of SREBP1 or fatty acid synthase changed basal expression of the core death receptor components Fas, caspase 8, FADD, caspase 3 or FLIP. Thus, inhibition of SREBP1 or its downstream target fatty acid synthase sensitizes resistant cells to death ligands.
authors.affiliation: Princess Margaret Hospital, Ontario Cancer Institute, Toronto, ON, Canada.
authors.forename: Yanina
authors.initials: Y
authors.lastname: Eberhard
authors.forename: Marcela
authors.initials: M
authors.lastname: Gronda
authors.forename: Rose
authors.initials: R
authors.lastname: Hurren
authors.forename: Alessandro
authors.initials: A
authors.lastname: Datti
authors.forename: Neil
authors.initials: N
authors.lastname: MacLean
authors.forename: Troy
authors.initials: T
authors.lastname: Ketela
authors.forename: Jason
authors.initials: J
authors.lastname: Moffat
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Wrana
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Schimmer
mesh_terms: D000906:Antibodies / Q000494:pharmacology*; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D016923:Cell Death; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D064429:Fatty Acid Synthases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D007783:Lactones / Q000494:pharmacology; D008024:Ligands; D000077403:Orlistat; D034741:RNA, Small Interfering / Q000008:administration & dosage / Q000235:genetics; D053218:Receptors, Death Domain / Q000378:metabolism; D051780:Sterol Regulatory Element Binding Protein 1 / Q000037:antagonists & inhibitors* / Q000235:genetics; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D014162:Transfection; D019014:fas Receptor / Q000096:biosynthesis
chemical_list: D000906:Antibodies; C481004:CH-11 anti-fas antibody, human; D004791:Enzyme Inhibitors; D007783:Lactones; D008024:Ligands; D034741:RNA, Small Interfering; D053218:Receptors, Death Domain; C497387:SREBF1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; D053221:TNF-Related Apoptosis-Inducing Ligand; D019014:fas Receptor; D000077403:Orlistat; D064429:Fatty Acid Synthases; D053148:Caspase 3; D053181:Caspase 8