title: A genome scale RNAi screen identifies GLI1 as a novel gene regulating vorinostat sensitivity.
abstract: Vorinostat is an FDA-approved histone deacetylase inhibitor (HDACi) that has proven clinical success in some patients; however, it remains unclear why certain patients remain unresponsive to this agent and other HDACis. Constitutive STAT (signal transducer and activator of transcription) activation, overexpression of prosurvival Bcl-2 proteins and loss of HR23B have been identified as potential biomarkers of HDACi resistance; however, none have yet been used to aid the clinical utility of HDACi. Herein, we aimed to further elucidate vorinostat-resistance mechanisms through a functional genomics screen to identify novel genes that when knocked down by RNA interference (RNAi) sensitized cells to vorinostat-induced apoptosis. A synthetic lethal functional screen using a whole-genome protein-coding RNAi library was used to identify genes that when knocked down cooperated with vorinostat to induce tumor cell apoptosis in otherwise resistant cells. Through iterative screening, we identified 10 vorinostat-resistance candidate genes that sensitized specifically to vorinostat. One of these vorinostat-resistance genes was GLI1, an oncogene not previously known to regulate the activity of HDACi. Treatment of vorinostat-resistant cells with the GLI1 small-molecule inhibitor, GANT61, phenocopied the effect of GLI1 knockdown. The mechanism by which GLI1 loss of function sensitized tumor cells to vorinostat-induced apoptosis is at least in part through interactions with vorinostat to alter gene expression in a manner that favored apoptosis. Upon GLI1 knockdown and vorinostat treatment, BCL2L1 expression was repressed and overexpression of BCL2L1 inhibited GLI1-knockdown-mediated vorinostat sensitization. Taken together, we present the identification and characterization of GLI1 as a new HDACi resistance gene, providing a strong rationale for development of GLI1 inhibitors for clinical use in combination with HDACi therapy.
authors: Cancer Therapeutics Program, The Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, VIC 3002, Australia.
authors: K J
authors: KJ
authors: Falkenberg
authors: Cancer Therapeutics Program, The Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, VIC 3002, Australia.
authors: A
authors: A
authors: Newbold
authors: Victorian Centre for Functional Genomics, The Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, VIC 3002, Australia.
authors: C M
authors: CM
authors: Gould
authors: Victorian Centre for Functional Genomics, The Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, VIC 3002, Australia.
authors: J
authors: J
authors: Luu
authors: Cancer Immunology Program, The Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, VIC 3002, Australia.|Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC 3052, Australia.
authors: J A
authors: JA
authors: Trapani
authors: Cancer Therapeutics Program, The Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, VIC 3002, Australia.|Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC 3052, Australia.
authors: G M
authors: GM
authors: Matthews
authors: Victorian Centre for Functional Genomics, The Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, VIC 3002, Australia.|Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC 3052, Australia.
authors: K J
authors: KJ
authors: Simpson
authors: Cancer Therapeutics Program, The Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, VIC 3002, Australia.|Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC 3052, Australia.
authors: R W
authors: RW
authors: Johnstone
mesh_terms: D000107:Acetylation / Q000187:drug effects; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D015894:Genome, Human; D045325:HCT116 Cells; D056572:Histone Deacetylase Inhibitors / Q000633:toxicity*; D006657:Histones / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D034622:RNA Interference; D015854:Up-Regulation / Q000187:drug effects; D000077337:Vorinostat; D000071676:Zinc Finger Protein GLI1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; C494811:BCL2L1 protein, human; C551027:GANT 61; C400551:GLI1 protein, human; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D019253:Proto-Oncogene Proteins c-bcl-2; D011725:Pyridines; D011743:Pyrimidines; D000071676:Zinc Finger Protein GLI1; D051020:bcl-X Protein; D000077337:Vorinostat; D053148:Caspase 3; D053179:Caspase 7