IGSF4 promoter methylation and expression silencing in human cervical cancer.

OBJECTIVES

Functional assays of tumor suppression and loss of heterozygosity point to a tumor suppressor gene (TSG) for cervical cancer (CC) on chromosome 11q23. We evaluated IGSF4, a putative TSG located in the region, for promoter methylation and gene silencing in CC cell lines and cervical tissues.

METHODS

IGSF4 expression was detected by both RT-PCR and Northern blot analysis. Methylation maps of the IGSF4 promoter region were generated for 11 CC cell lines based upon bisulfite-genomic sequencing, using seven nested-PCR primer sets covering 97 CpG sites. Methylation fingerprints in primary cervical tissues were evaluated by denaturing high performance liquid chromatography.

RESULTS

A 4.4-kb mRNA was seen in cell lines, consistent with the RT-PCR results for both cell lines and primary cervical tissue. IGSF4 was expressed in 6/11 cell lines, 6/8 CC tissues and in all seven normal cervical epithelia. In the cell lines, IGSF4 silencing was associated with promoter hypermethylation. The methylation status in the region covering the -18 to -2 CpG sites correlated most strongly with expression, pointing to the existence of an unmethylated core in the IGSF4 promoter in cell lines expressing IGSF4. This unmethylated core spans approximately 180 bp and is immediately upstream of the ATG site. In primary tissues, methylation was detected in 15/23 (65%) CC specimens but in none of seven normal cervical epithelia.

CONCLUSIONS

Our data strongly suggest that IGSF4 is a TSG and that gene silencing by aberrant hypermethylation may contribute to the development of CC.