Frequent inactivation of hSRBC in ovarian cancers by promoter CpG island hypermethylation

Abstract

Objective. To explore the implication of human SRBC gene [serum deprivation response factor-related gene product that binds to the c-kinase (hSRBC)] abnormality in ovarian tumorigenesis. Design. Retrospective study. Setting. Medical center. Sample. Twenty-two epithelial ovarian cancer and six normal ovary tissues. Measures. Mutation and altered expression of hSRBC gene. Methods. hSRBC expression was characterized by polymerase chain reaction (PCR) analysis. Promoter CG dinucleotide (CpG) site methylation was determined using methylation specific PCR and bisulfite sequencing. Results. Expression of hSRBC transcript was easily detectable in all normal tissues we examined, but 50% (two of four) of cancer cell lines and 41% (nine of 22) of primary carcinomas exhibited undetectable or substantially decreased expression. While genomic deletion or somatic mutations of the gene was not identified, its expression was reactivated in tumor cells by 5-aza-2'-deoxycytidine treatment, suggesting epigenetic inactivation of the gene in tumors. Promoter methylation was detected in all nine tumors with low expression but in only one of 13 (7.7%) tumors with normal expression. Bisulfite DNA sequencing analysis of 23 CpG sites within the promoter region revealed that the CpG sites are highly methylated in low-expressing tumors. In addition, promoter CpG sites methylation status showed a tight association with gene expression level. Conclusion. Our data demonstrate that epigenetic inactivation of hSRBC due to aberrant promoter hypermethylation is a common event and might be implicated in human ovarian tumorigenesis.