Aberrant promoter methylation and silencing of the POU2F3 gene in cervical cancer

Abstract

POU2F3 (OCT11, Skn-1a) is a keratinocyte-specific POU transcription factor whose expression is tied to squamous epithelial stratification. It is also a candidate tumor suppressor gene in cervical cancer (CC) because it lies in a critical loss of heterozygosity region on11q23.3 in that cancer, and its expression is lost in more than 50% of CC tumors and cell lines. We now report that the loss of POU2F3 expression is tied to the hypermethylation of CpG islands in the POU2F3 promoter. Bisulfite sequencing analysis revealed that methylation of specific CpG sites (À287 to À70 bp) correlated with POU2F3 expression, which could be reactivated with a demethylating agent. Combined bisulfite restriction analysis revealed aberrant methylation of the POU2F3 promoter in 18 of 46 (39%) cervical tumors but never in normal epithelium. POU2F3 expression was downregulated and inversely correlated with promoter hypermethylation in 10 out of 11 CC cell lines. Immunohistochemical analysis on a cervical tissue microarray detected POU2F3 protein in the epithelium above the basal layer. As the disease progressed, expression also decreased, especially in invasive squamous cell cancer (70% loss). Thus, aberrant DNA methylation of the CpG island in POU2F3 promoter appears to play a key role in silencing this gene expression in human CC. The results suggested that POU2F3 might be one of the CC-related tumor suppressor genes, which are disrupted by both epigenetic and genetic mechanisms.

Retinoic Acid Receptor β Silences Human Papillomavirus-18 Oncogene Expression by Induction of de Novo Methylation and Heterochromatinization of the Viral Control Region

“…This indicates that there were apparently no differences in methylation in general between parental HeLa cells or RAR␤ expressing clones. Notably, treatment of cells with decitabine did not induce demethylation of the Ha-Ras 3Ј-VTR, which is consistent with previous reports showing that certain genes were refractory to demethylation (46,47). In contrast, when RAR␤ expressing clones were treated under the same experimental conditions, the 254-bp fragment could no longer be amplified, indicating that demethylation of the HPV-18 enhancer was successful (Fig.…”

Genetic redundancy in human cervical carcinoma cells: Identification of cells with “normal” properties

“…However, even though epigenetic states are potentially reversible, treatment with agents generally affecting DNA methylation have their natural limitation due to their non-selectivity and sometimes also because of their inefficiency to demethylate particular CpG sequences. 41,42 Moreover, simultaneous change of a whole network of epigenetically silenced genes by inhibitory drugs may negatively interfere with the final outcome of a proper immunological response. 43 In fact, preincubation with sodium butyrate did not unmask those cells selected by our method (Fig.…”

Octamer-binding transcription factors: genomics and functions

“…Oct11 expression is lost in more than 50% of cervical tumors and cell lines. Silencing of the Oct11 gene by aberrant DNA methylation of its promoter has been observed in 39% of cervical tumors but has not been noted in normal epithelium (195). …”