title: Imprinted tumor suppressor genes ARHI and PEG3 are the most frequently down-regulated in human ovarian cancers by loss of heterozygosity and promoter methylation.
abstract: BACKGROUND
  Imprinted tumor suppressor genes may be particularly important in the pathogenesis of ovarian cancer. Two imprinted genes, paternally expressed 3 (PEG3) and aplasia Ras homologue member I (ARHI), are the most frequently down-regulated in ovarian cancers on gene expression arrays.
  
  
  METHODS
  PEG3 and ARHI expression levels were evaluated with real-time reverse-transcriptase polymerase chain reaction (PCR) analysis. Promoter methylation was measured by pyrosequencing, and loss of heterozygosity (LOH) was detected by PCR-LOH assays.
  
  
  RESULTS
  PEG3 was down-regulated in 75% and ARHI was down-regulated in 88% of 40 ovarian cancers. ARHI CpG islands I and II were hypermethylated in 13 of 42 ovarian cancers (31%) and in 5 of 42 ovarian cancers (12%), respectively, and hypermethylation was associated with reduced ARHI expression in all 18 samples of ovarian cancer with CpG island hypermethylation. PEG3 was hypermethylated in 11 of 42 ovarian cancers (26%), and PEG3 expression was down-regulated in 10 of those 11 cancers. LOH was detected in 8 of 35 informative cases for ARHI (23%) and in 5 of 25 informative cases for PEG3 (20%). PEG3 and ARHI expression was highly correlated in human ovarian cancers (correlation coefficient [R]=0.69; P< .0001). PEG3 and ARHI also were methylated concordantly in ovarian cancers (R=0.36; P= .019). Re-expression of PEG3, similar to that of ARHI, markedly inhibited ovarian cancer growth. ARHI and PEG3 expression could be restored by treatment with 5-aza-2'-deoxycytidine and trichostatin A, consistent with the importance of promoter methylation and histone acetylation in regulating expression of both genes.
  
  
  CONCLUSIONS
  Loss of expression of the growth-inhibitory imprinted genes ARHI and PEG3 through promoter methylation, LOH, and other mechanisms may stimulate clonogenic growth and contribute to the pathogenesis of a majority of ovarian cancers.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030-4009, USA.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Feng
authors.forename: Rebecca T
authors.initials: RT
authors.lastname: Marquez
authors.forename: Zhen
authors.initials: Z
authors.lastname: Lu
authors.forename: Jinsong
authors.initials: J
authors.lastname: Liu
authors.forename: Karen H
authors.initials: KH
authors.lastname: Lu
authors.forename: Jean-Pierre J
authors.initials: JP
authors.lastname: Issa
authors.forename: David M
authors.initials: DM
authors.lastname: Fishman
authors.forename: Yinhua
authors.initials: Y
authors.lastname: Yu
authors.forename: Robert C
authors.initials: RC
authors.lastname: Bast
mesh_terms: D018262:Adenocarcinoma, Clear Cell / Q000235:genetics / Q000556:secondary; D002288:Adenocarcinoma, Mucinous / Q000235:genetics / Q000556:secondary; D018269:Carcinoma, Endometrioid / Q000235:genetics / Q000556:secondary; D016022:Case-Control Studies; D018899:CpG Islands; D018284:Cystadenocarcinoma, Serous / Q000235:genetics / Q000556:secondary; D019175:DNA Methylation; D017931:DNA Primers / Q000737:chemistry; D015536:Down-Regulation; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor / Q000502:physiology; D018392:Genomic Imprinting; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000235:genetics*; D019656:Loss of Heterozygosity; D020411:Oligonucleotide Array Sequence Analysis; D010051:Ovarian Neoplasms / Q000235:genetics* / Q000473:pathology; D010053:Ovary / Q000378:metabolism / Q000473:pathology; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D020741:rho GTP-Binding Proteins / Q000235:genetics*
chemical_list: C117386:DIRAS3 protein, human; D017931:DNA Primers; D051741:Kruppel-Like Transcription Factors; C490820:PEG3 protein, human; D012333:RNA, Messenger; D020741:rho GTP-Binding Proteins