Methylation‐associated silencing of the Wnt antagonist SFRP1 gene in human ovarian cancers

Abstract

The SFRP1 gene on chromosome 8p11.2 encodes a Wnt signaling antagonist, and was recently demonstrated to be a new tumor suppressor that is inactivated by promoter methylation in human colon cancers. Here, we analyzed promoter methylation of the SFRP1 gene in human ovarian cancers, in which loss of heterozygosity in 8p is frequently observed and involvement of the Wnt signaling pathway has been suggested. Methylation-specific PCR (MSP) analysis showed that four of 13 ovarian cancer cell lines and two of 17 primary ovarian cancers had methylated SFRP1, while an immortalized ovarian epithelial cell line, HOSE, and seven ovarian endometrial cyst samples did not. In the four ovarian cancer cell lines with the methylation, SFRP1 was not expressed at all as determined by quantitative RT-PCR analysis. A cell line with SFRP1 methylation, MCAS, was treated with a demethylating agent, 5-aza-2'-deoxycytidine, and demethylation of the promoter and re-expression of SFRP1 were observed. These results show that SFRP1 is inactivated by promoter methylation in human ovarian cancers, as well as colon cancers. varian cancer is the most lethal gynecological malignancy, and is characterized by the diversity of its histology.1) The four major histological subtypes, serous, clear cell, mucinous, and endometrioid, constitute approximately 36, 19, 14, and 15% of the total, respectively, in Japan, 2) and all of these are considered to be derived from ovarian surface epithelium.3) As for genetic alterations, only limited information is available, such as mutations of β-catenin in 31% of endometrioid type 4,5) and c-erbB-2 amplification in serous type with poor prognosis.6) Due to promoter methylation, BRCA1, hMLH1, and RASSF1A are inactivated (silenced) in 10%, 7) 12.5%, 8) and 10-40% of ovarian cancers, 9, 10) respectively. Clarification of molecular alterations is important to identify novel diagnostic and therapeutic targets, and further investigations in ovarian cancers are necessary.Secreted frizzled-related proteins (SFRPs) are extracellular signaling molecules that antagonize the Wnt signaling pathway.11, 12) SFRP1 (8p11.2) is inactivated in colorectal cancers by promoter methylation [13][14][15] and also by infrequent mutations.15) Other members, SFRP2 (4q31.3) and SFRP5 (10q24.1), are also inactivated by promoter methylation in colorectal cancers.14) Strikingly, the inactivation of SFRP genes enhanced the constitutive Wnt signaling even in the presence of APC or β-catenin mutations.14, 15) In ovarian cancers, SFRP inactivation could also potentially be present for the following reasons. First, the Wnt signaling pathway can be affected in ovarian cancers, as indicated by the presence of β-catenin mutations in cancers of the endometrioid type. 4,5) Second, in the serous type, in spite of increased β-catenin accumulation, 16) β-catenin mutations are infrequent, 17) and abnormality in other genes in the Wnt signaling pathway is suggested.In this study, we analyzed methylation-associated silencing of the SFRP1 gene on chromosome 8p11.2...

Epigenetic inactivation of TCF2 in ovarian cancer and various cancer cell lines

“…We and others have reported that TMS1, 14-3-3sigma and WT1 genes are methylated more frequently in clear cell tumours than in other tumour types (Kaneuchi et al, 2004;Terasawa et al, 2004;Kaneuchi et al, 2005), whereas methylation of SFRP1, 18S and 28S ribosomal DNA genes is more frequently detected in nonclear cell tumours, such as the serous type (Takada et al, 2004;Chan et al, 2005). Although the molecular mechanisms responsible for the differing methylation profiles in different tumour types remains unclear, gene methylation may have relevance in the clinical situation.…”

Tissue microarray analysis of human FRAT1 expression and its correlation with the subcellular localisation of β-catenin in ovarian tumours

“…It has been suggested that downregulated expression of APC (Karbova et al, 2002) or secreted frizzled-related proteins (SFRPs) inactivation by methylation (Takada et al, 2004) could explain, at least partially, why ovarian serous adenocarcinomas show increased b-catenin protein expression in spite of the absence of gene mutation. However, none of these studies has shown any statistical correlation between these molecules and subcellular localisation of b-catenin in tissue samples (Karbova et al, 2002;Takada et al, 2004). Whether deregulation of these molecules contributes to the accumulation of b-catenin in ovarian serous adenocarcinomas is yet to be established.…”

HAND1 gene expression is negatively regulated by the High Mobility Group A1 proteins and is drastically reduced in human thyroid carcinomas

“…The mechanisms, however, which initiate and maintain HAND1 expression in extraembryonic cell types are not well known. A role of HAND1 in cell proliferation and neoplastic transformation has been recently envisaged because HAND1 gene has been found silenced and hypermethylated in human gastric (Kaneda et al, 2002), pancreatic (Hagihara et al, 2004) and ovarian carcinomas (Takada et al, 2004).…”