title: Dysregulation of the repressive H3K27 trimethylation mark in head and neck squamous cell carcinoma contributes to dysregulated squamous differentiation.
abstract: OBJECTIVE
  Head and neck squamous cell carcinoma (HNSCC) is one of the most prevalent cancers diagnosed worldwide and is associated with a 5-year survival rate of 55%. EZH2, a component of the polycomb repressor complex 2, trimethylates H3K27 (H3K27me3), which has been shown to drive squamous differentiation in normal keratinocytes. This study determined whether inhibition of EZH2-mediated epigenetic silencing could induce differentiation or provide therapeutic benefit in HNSCC.
  
  
  METHODS
  We determined the effects of inhibiting EZH2, by either RNA interference or pharmacologically, on HNSCC growth, viability, and differentiation in vitro. Xenografts of HNSCC cell lines were used to assess efficacy of 3-deazaneplanocin A (DZNep), an inhibitor of H3K27 trimethylation, in vivo.
  
  
  RESULTS
  EZH2 was highly expressed in HNSCC cell lines in vitro and tissue microarray analysis revealed high expression in (n = 59) in situ relative to normal oral epithelium (n = 12). Inhibition of EZH2 with siRNA could induce expression of differentiation genes in differentiation-refractory squamous cell carcinoma cell lines. Differentiation-refractory HNSCC cell lines displayed persistent H3K27me3 on the promoters of differentiation genes. DZNep caused cancer-cell-specific apoptosis in addition to a profound reduction in colony-forming efficiency and induction of some squamous differentiation genes. Furthermore, in vivo, DZNep attenuated tumor growth in two different xenograft models, caused intratumor inhibition of EZH2, and induction of differentiation genes in situ.
  
  
  CONCLUSIONS
  Collectively, these data suggest that aberrant differentiation in HNSCC may be attributed to epigenetic dysregulation and suggest that inhibition of PRC2-mediated gene repression may represent a potential therapeutic target.
authors.affiliation: University of Queensland Diamantina Institute, Princess Alexandra Hospital, Ipswich Road, Woolloongabba, Queensland, Australia.
authors.forename: Orla M
authors.initials: OM
authors.lastname: Gannon
authors.forename: Lilia
authors.initials: L
authors.lastname: Merida de Long
authors.forename: Liliana
authors.initials: L
authors.lastname: Endo-Munoz
authors.forename: Mehlika
authors.initials: M
authors.lastname: Hazar-Rethinam
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Saunders
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D000071221:Enhancer of Zeste Homolog 2 Protein; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006258:Head and Neck Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D006657:Histones / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008745:Methylation; D051379:Mice; D063151:Polycomb Repressive Complex 2 / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D000077195:Squamous Cell Carcinoma of Head and Neck; D014183:Transplantation, Heterologous
chemical_list: D006657:Histones; C048460:3-deazaneplanocin; C498409:EZH2 protein, human; D000071221:Enhancer of Zeste Homolog 2 Protein; D063151:Polycomb Repressive Complex 2; D000241:Adenosine