title: Glutathione peroxidase 7 has potential tumour suppressor functions that are silenced by location-specific methylation in oesophageal adenocarcinoma.
abstract: OBJECTIVE
  To investigate the potential tumour suppressor functions of glutathione peroxidase 7 (GPX7) and examine the interplay between epigenetic and genetic events in regulating its expression in oesophageal adenocarcinomas (OAC).
  
  
  METHODS
  In vitro and in vivo cell models were developed to investigate the biological and molecular functions of GPX7 in OAC.
  
  
  RESULTS
  Reconstitution of GPX7 in OAC cell lines, OE33 and FLO-1, significantly suppressed growth as shown by the growth curve, colony formation and EdU proliferation assays. Meanwhile, GPX7-expressing cells displayed significant impairment in G1/S progression and an increase in cell senescence. Concordant with the above functions, Western blot analysis displayed higher levels of p73, p27, p21 and p16 with a decrease in phosphorylated retinoblastoma protein (RB), indicating its increased tumour suppressor activities. On the contrary, knockdown of GPX7 in HET1A cells (an immortalised normal oesophageal cell line) rendered the cells growth advantage as indicated with a higher EdU rate, lower levels of p73, p27, p21 and p16 and an increase in phosphorylated RB. We confirmed the tumour suppressor function in vivo using GPX7-expressing OE33 cells in a mouse xenograft model. Pyrosequencing of the GPX7 promoter region (-162 to +138) demonstrated location-specific hypermethylation between +13 and +64 in OAC (69%, 54/78). This was significantly associated with the downregulation of GPX7 (p<0.01). Neither mutations in the coding exons of GPX7 nor DNA copy number losses were frequently present in the OAC examined (<5%).
  
  
  CONCLUSIONS
  Our data suggest that GPX7 possesses tumour suppressor functions in OAC and is silenced by location-specific promoter DNA methylation.
authors.affiliation: Department of Veterans Affairs, Tennessee Valley Healthcare System, , Nashville, Tennessee, USA.
authors.forename: DunFa
authors.initials: D
authors.lastname: Peng
authors.forename: TianLing
authors.initials: T
authors.lastname: Hu
authors.forename: Mohammed
authors.initials: M
authors.lastname: Soutto
authors.forename: Abbes
authors.initials: A
authors.lastname: Belkhiri
authors.forename: Alexander
authors.initials: A
authors.lastname: Zaika
authors.forename: Wael
authors.initials: W
authors.lastname: El-Rifai
mesh_terms: D000230:Adenocarcinoma / Q000201:enzymology* / Q000378:metabolism / Q000503:physiopathology; D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019175:DNA Methylation / Q000502:physiology*; D004273:DNA, Neoplasm / Q000502:physiology; D004938:Esophageal Neoplasms / Q000201:enzymology* / Q000378:metabolism / Q000503:physiopathology; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D020868:Gene Silencing; D005979:Glutathione Peroxidase; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010544:Peroxidases / Q000378:metabolism / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000378:metabolism / Q000502:physiology*
chemical_list: D004273:DNA, Neoplasm; D025521:Tumor Suppressor Proteins; D010544:Peroxidases; C558641:GPX7 protein, human; D005979:Glutathione Peroxidase
keywords: CANCER; CELL CYCLE; GASTROINTESTINAL CANCER; OESOPHAGEAL CANCER