title: Epigenetic differences between human papillomavirus-positive and -negative oropharyngeal squamous cell carcinomas.
abstract: BACKGROUND
  Epigenetic modifications are defined as heritable changes in gene expression that are not encoded in deoxyribonucleic acid (DNA). Despite the importance of epigenetics in tumorigenesis, there is a paucity of information regarding the epigenetic profiles of oropharyngeal squamous cell carcinoma (OPSCC).
  
  
  OBJECTIVE
  The objective of this study was to identify epigenetic signatures associated with human papillomavirus (HPV)-positive and -negative OPSCC.
  
  
  METHODS
  We collected demographic, pathologic, and survival data from 44 patients with advanced-stage OPSCC treated with surgery and chemoradiation at the University of Alberta between January 2006 and December 2008. Tumour specimen from these patients were retreived and sectioned for immunohistochemical analysis. Double immunofluorescence staining was performed with p16 (HPV surrogate) and a panel of epigenetic markers, namely, histone methyl-lysines 4, 9, and 27 and H4 methyl-lysine 20. Correlation between p16 and epigenetic markers was measured using Metamorph and Image J software.
  
  
  RESULTS
  Forty-one percent of patients were p16 positive. No statistically significant differences were found between p16-positive and -negative patients in terms of age at diagnosis, tumour subsite, or smoking history. We found significant differences in histone methylation between p16-positive and -negative tumours. OPSCC tumours positive for p16 had global elevations of histone H4 monomethylated lysine 20 (H4K20me1) and H3 trimethylated lysine 27 (H3K27me3) with depletions of H4 trimethylated lysine 20 (H4K20me3). In contrast, p16-negative tumours had depleted levels of H4K20me1 and H3K27me3 with high levels of H4K20me3.
  
  
  CONCLUSIONS
  HPV-positive and -negative OPSCCs have distinct epigenetic profiles representing broad gene expression differences between these tumours.
authors.affiliation: Division of Otolaryngology-Head and Neck Surgery, Department of Surgery, Michael J Hendzel and D Alan Underhill, Undergraduate Education, University of Alberta, Edmonton, AB.
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Biron
authors.forename: Adil
authors.initials: A
authors.lastname: Mohamed
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Hendzel
authors.forename: D
authors.initials: D
authors.lastname: Alan Underhill
authors.forename: Hadi
authors.initials: H
authors.lastname: Seikaly
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis / Q000235:genetics; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000473:pathology / Q000821:virology*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis / Q000235:genetics*; D004279:DNA, Viral / Q000032:analysis*; D057890:Epigenomics / Q000379:methods*; D005260:Female; D005819:Genetic Markers; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D009959:Oropharyngeal Neoplasms / Q000235:genetics / Q000473:pathology / Q000821:virology*; D027383:Papillomaviridae / Q000201:enzymology / Q000235:genetics*; D030361:Papillomavirus Infections / Q000235:genetics / Q000473:pathology / Q000821:virology*; D011379:Prognosis; D012189:Retrospective Studies
chemical_list: D014408:Biomarkers, Tumor; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004279:DNA, Viral; D005819:Genetic Markers