Epigenetic inactivation of TMS1/ASC in ovarian cancer.
OBJECTIVE
The purpose of this work was to explore the role of epigenetic inactivation of apoptotic pathways in ovarian cancer by examining the DNA methylation and expression status of four proapoptotic genes in primary ovarian cancers and cancer cell lines and to correlate those findings with the clinicopathological features of ovarian cancer patients.


METHODS
Genomic DNA was isolated from 15 ovarian cancer cell lines, 80 primary ovarian cancer specimens, and 4 normal ovary specimens using phenol-chloroform extraction. The methylation status of the DNA was evaluated using combined bisulfite restriction analysis, gene expression was evaluated using reverse transcription-PCR, and histone acetylation was evaluated using chromatin immunoprecipitation.


RESULTS
Of the four proapoptotic genes studied, expression of TMS1/ASC was absent in six ovarian cancer cell lines. Dense methylation of the 5' region of TMS1/ASC was detected in cells not expressing TMS1/ASC. Treating methylated cells with 5-aza-deoxycytidine restored gene expression, confirming the role of methylation in silencing the gene. Chromatin immunoprecipitation revealed histone to be deacetylated in cells not expressing TMS1/ASC, indicating that histone deacetylation is also involved in silencing TMS1/ASC. Aberrant methylation of TMS1/ASC was detected in 15 of 80 ovarian cancer tissues (19%) but in none of the normal ovary specimens. Aberrant methylation of TMS1/ASC was observed significantly more often in clear cell-type ovarian cancers than in other tumor types (P < 0.0001).


CONCLUSIONS
Methylation-mediated silencing of TMS1/ASC confers a survival advantage to tumor cells by enabling them to escape apoptosis. The role for aberrant methylation in human ovarian tumorigenesis may be particularly important for ovarian cancers with the clear cell phenotype.
Terasawa
Katsuhiko
K
Departments of Obstetrics and Gynecology, Sapporo Medical University, Sapporo, Japan. kterasaw@sapmed.ac.jp
Sagae
Satoru
S
Toyota
Minoru
M
Tsukada
Kuniko
K
Ogi
Kazuhiro
K
Satoh
Ayumi
A
Mita
Hiroaki
H
Imai
Kohzoh
K
Tokino
Takashi
T
Kudo
Ryuichi
R
D017209:Apoptosis / Q000235:genetics; D001483:Base Sequence; D053468:CARD Signaling Adaptor Proteins; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D003598:Cytoskeletal Proteins / Q000235:genetics*; D019175:DNA Methylation; D017931:DNA Primers; D004273:DNA, Neoplasm / Q000235:genetics; D005260:Female; D020868:Gene Silencing; D006655:Histone Deacetylases / Q000235:genetics; D006801:Humans; D010051:Ovarian Neoplasms / Q000235:genetics* / Q000473:pathology; D011506:Proteins / Q000235:genetics*; D015183:Restriction Mapping
D053468:CARD Signaling Adaptor Proteins; D003598:Cytoskeletal Proteins; D017931:DNA Primers; D004273:DNA, Neoplasm; C402202:PYCARD protein, human; D011506:Proteins; D006655:Histone Deacetylases