title: Imprinted CDKN1C is a tumor suppressor in rhabdoid tumor and activated by restoration of SMARCB1 and histone deacetylase inhibitors.
abstract: SMARCB1 is deleted in rhabdoid tumor, an aggressive paediatric malignancy affecting the kidney and CNS. We hypothesized that the oncogenic pathway in rhabdoid tumors involved epigenetic silencing of key cell cycle regulators as a consequence of altered chromatin-remodelling, attributable to loss of SMARCB1, and that this hypothesis if proven could provide a biological rationale for testing epigenetic therapies in this disease. We used an inducible expression system to show that the imprinted cell cycle inhibitor CDKN1C is a downstream target for SMARCB1 and is transcriptionally activated by increased histone H3 and H4 acetylation at the promoter. We also show that CDKN1C expression induces cell cycle arrest, CDKN1C knockdown with siRNA is associated with increased proliferation, and is able to compete against the anti-proliferative effect of restored SMARCB1 expression. The histone deacetylase inhibitor (HDACi), Romidepsin, specifically restored CDKN1C expression in rhabdoid tumor cells through promoter histone H3 and H4 acetylation, recapitulating the effect of SMARCB1 on CDKNIC allelic expression, and induced cell cycle arrest in G401 and STM91-01 rhabdoid tumor cell lines. CDKN1C expression was also shown to be generally absent in clinical specimens of rhabdoid tumor, however CDKN1A and CDKN1B expression persisted. Our observations suggest that maintenance of CDKN1C expression plays a critical role in preventing rhabdoid tumor growth. Significantly, we report for the first time, parallels between the molecular pathways of SMARCB1 restoration and Romidepsin treatment, and demonstrate a biological basis for the further exploration of histone deacetylase inhibitors as relevant therapeutic reagents in the treatment of rhabdoid tumor.
authors.affiliation: Children's Cancer Centre research laboratory, Murdoch Children's Research Institute, Royal Children's Hospital, Parkville, Australia. elizabeth.algar@rch.org.au
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Algar
authors.forename: Andrea
authors.initials: A
authors.lastname: Muscat
authors.forename: Vinod
authors.initials: V
authors.lastname: Dagar
authors.forename: Christian
authors.initials: C
authors.lastname: Rickert
authors.forename: C W
authors.initials: CW
authors.lastname: Chow
authors.forename: Jaclyn A
authors.initials: JA
authors.lastname: Biegel
authors.forename: Paul G
authors.initials: PG
authors.lastname: Ekert
authors.forename: Richard
authors.initials: R
authors.lastname: Saffery
authors.forename: Jeff
authors.initials: J
authors.lastname: Craig
authors.forename: Ricky W
authors.initials: RW
authors.lastname: Johnstone
authors.forename: David M
authors.initials: DM
authors.lastname: Ashley
mesh_terms: D000107:Acetylation; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation; D002648:Child; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D047630:Depsipeptides / Q000378:metabolism; D018392:Genomic Imprinting; D056572:Histone Deacetylase Inhibitors; D006657:Histones / Q000378:metabolism; D006801:Humans; D007223:Infant; D051379:Mice; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D018335:Rhabdoid Tumor / Q000235:genetics / Q000378:metabolism*; D000071796:SMARCB1 Protein; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000903:Antibiotics, Antineoplastic; C493964:CDKN1C protein, human; D002868:Chromosomal Proteins, Non-Histone; D050761:Cyclin-Dependent Kinase Inhibitor p57; D004268:DNA-Binding Proteins; D047630:Depsipeptides; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D034741:RNA, Small Interfering; D000071796:SMARCB1 Protein; C513266:SMARCB1 protein, human; D014157:Transcription Factors; C087123:romidepsin