Epigenetic silencing of the candidate tumor suppressor gene PROX1 in sporadic breast cancer

Objective: Differential methylation of cancer associated genes plays a pivotal role in tumor development. Several studies using candidate gene analyses or genome wide approaches suggest that these alterations occur in a non-random fashion and affect genes with various function in all cancer entities. The purpose of this study was to identify novel genes affected by de novo methylation in breast carcinomas. Materials and Methods: Therefore, we compared the methylation status of 7680 CpG-rich fragments of the human genome in 10 primary breast carcinomas (BrCa) and corresponding normal tissues (NT) by CpG island microarray analysis. Differentially methylated sequences were confirmed by bisulfite (BS) genomic sequencing of 10 pairs of BrCa and corresponding NT. In addition quantitative RT-PCR analysis was performed in 32 pairs of BrCa and corresponding NT. Results: One of the sequences identified by CpG island microarray analysis was identical with the promotor region and exon 1 of the prospero-related homeobox 1 gene (PROX1). Confirmation of the methylation status by BS sequencing of the 5' CpG-rich region of PROX1 revealed hypermethylation in 7 out of 10 analyzed tumor samples. Moreover, hypermethylation corresponds to a decreased transcription, that was detected in 27 of 32 tested tumors. Discussion: In summary, we have identified PROX1 as a new target epigenetically silenced in sporadic breast cancer. Lack of PROX1 gene product has been associated with down regulation of the cell-cycle inhibitors CDKN1B and CDKN1C and abnormal cellular proliferation. Since this gene has already been shown to be affected by mutation and differential methylation in other cancer entities, we postulate PROX1 to exhibit a general tumor suppressor function.

Eingereicht von: Beatrix Versmold

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