Promoter hypermethylation profile of ovarian epithelial neoplasms.
OBJECTIVE
Ovarian carcinomas are believed to arise de novo from surface epithelium, but the actual molecular pathogenesis is unknown. The aim of this study was to compare the promoter hypermethylation profiles of ovarian epithelial neoplasms to better understand the role of epigenetic silencing in carcinogenesis.


METHODS
We analyzed the DNA promoter methylation status of eight tumor suppressor and cancer-related genes (p16, RARbeta, E-cadherin,H-cadherin, APC, GSTP1, MGMT, RASSF1A) in 23 benign cystadenomas, 23 low malignant potential (LMP) tumors, and 23 invasive carcinomas by methylation-specific PCR.


RESULTS
Benign cystadenomas exhibited promoter hypermethylation in only two genes, p16 (13%) and E-cadherin (13%). LMP tumors also showed p16 (22%) and E-cadherin (17%) methylation, in addition to RARbeta (9%) and H-cadherin (4%). All eight genes were hypermethylated in invasive cancers at a frequency of 9% to 30%. The mean methylation index was highest in invasive tumors [0.20 versus 0.065 (LMP) and 0.033 (cystadenomas); P = 0.001]. Promoter methylation of at least one gene was most commonly observed among invasive cancers [78% versus 44% (LMP; P = 0.03) and 26% (cystadenomas; P = 0.0009)]. Three genes exhibited higher methylation frequencies in invasive tumors: RASSF1A (30% versus 0%; P = 0.0002), H-cadherin (22% versus 2%; P = 0.013), and APC (22% versus 0%; P = 0.003).


CONCLUSIONS
Promoter hypermethylation is a frequent epigenetic event that occurs most commonly in invasive epithelial ovarian carcinomas. The profile of aberrant methylation suggests that an accumulation of events at specific genes may trigger malignant transformation of some benign cystadenomas and LMP tumors.
Makarla
Prakash B
PB
Hamon Center for Therapeutic Oncology Research, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Saboorian
M Hossein
MH
Ashfaq
Raheela
R
Toyooka
Kiyomi O
KO
Toyooka
Shinichi
S
Minna
John D
JD
Gazdar
Adi F
AF
Schorge
John O
JO
D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015820:Cadherins / Q000235:genetics; D002277:Carcinoma / Q000235:genetics / Q000473:pathology; D002471:Cell Transformation, Neoplastic; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics; D003537:Cystadenoma / Q000235:genetics; D004247:DNA / Q000378:metabolism; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D020868:Gene Silencing; D051549:Glutathione S-Transferase pi / Q000235:genetics; D006801:Humans; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D009375:Neoplasms, Glandular and Epithelial / Q000235:genetics*; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics; D010051:Ovarian Neoplasms / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D018168:Receptors, Retinoic Acid / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics
D025601:Adenomatous Polyposis Coli Protein; D015820:Cadherins; D019941:Cyclin-Dependent Kinase Inhibitor p16; C099972:H-cadherin; C411762:RASSF1 protein, human; D018168:Receptors, Retinoic Acid; D025521:Tumor Suppressor Proteins; C082925:retinoic acid receptor beta; D004247:DNA; D019853:O(6)-Methylguanine-DNA Methyltransferase; C496556:GSTP1 protein, human; D051549:Glutathione S-Transferase pi