Imprinted tumor suppressor genes ARHI and PEG3 are the most frequently down-regulated in human ovarian cancers by loss of heterozygosity and promoter methylation.
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.
Feng
Weiwei
W
Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030-4009, USA.
Marquez
Rebecca T
RT
Lu
Zhen
Z
Liu
Jinsong
J
Lu
Karen H
KH
Issa
Jean-Pierre J
JP
Fishman
David M
DM
Yu
Yinhua
Y
Bast
Robert C
RC
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*
C117386:DIRAS3 protein, human; D017931:DNA Primers; D051741:Kruppel-Like Transcription Factors; C490820:PEG3 protein, human; D012333:RNA, Messenger; D020741:rho GTP-Binding Proteins