Epigenetic regulation of the KAI1 metastasis suppressor gene in human prostate cancer cell lines

Expression of the KAI1 gene, a metastasis-suppressor for prostate cancer, i s reduced in all foci of prostatic metastasis. The altered regulatory mecha nism is not strongly related to mutations or allelic losses of the KAI1 gen e in prostate tumors. Since transcriptional silencing of genes has been fou nd to be caused by epigenetic mechanisms, we have investigated the involvem ent of this epigenetic regulation of KAI1 expression in prostate cancers. T he methylation status of the KAI1 promoter region was examined by restricti on-enzyme digestion and sequencing, after amplifying a 331-bp fragment in t he GC-rich promoter region from 4 human prostate cancer cell lines treated with bisulfite. The same 4 cell lines were also exposed to various concentr ations of the demethylating agent, 5-aza-2'-deoxycytidine (5-AzaC) and/or t he histone deacetylase inhibitor, trichostatin A (TSA). To clarify the infl uence of epigenetic modification on reduced KAI1 mRNA expression in the tum or cells, RT-PCR and northern-blot analyses were performed. Bisulfite-seque ncing data showed a few methylated CpG islands in the promoter. RT-PCR anal ysis of 5-AzaC and/or TSA-treated cells indicated reversal of suppression o f KAI1 transcription in two cell lines (PC-3 and DU-145), although the expr ession could not be detected by northern blots. From these results, it is s uggested that epigenetic change is not the main mechanism of KAI1 down-regu lation, though there remains a possibility that methylation in a more upstr eam region might be associated with this regulation.