Survivin Expression is Regulated by an Epigenetic Mechanism for DMBA-induced Hamster Buccal-pouch Squamous-cell Carcinomas

Apoptosis, also known as programmed cell death, is regulated by a number of inhibitory or stimulatory factors. In addition to the pro- and anti-apoptotic Bcl-2 family proteins, there is also a family of inhibitors of apoptosis protein (IAP). Survivin, a member of this IAP family, is selectively upregulated in most tumours. The objective of the present study was, therefore, to investigate the protein and mRNA expression of survivin, as well as the methylation status of the CpG sites in exon 1 of the survivin gene for 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch squamous-cell carcinomas. Immunohistochemical analysis for protein expression, RT-PCR for mRNA expression, and a PCR-based methylation assay were performed on 26 samples of hamster buccal pouches. The total study population was assigned into either one experimental group (15-week DMBA treatment; n=13) or two control groups (untreated: n=6; mineral-oil treated n=7). Cytoplasmic staining of survivin protein and mRNA were detected in all of the hamster buccal-pouch tissue specimens treated with DMBA, whereas neither survivin protein nor survivin mRNA were noted for all of the untreated and mineral oil-treated hamster buccal-pouch tissue specimens. Furthermore, all the untreated and mineral-oil treated samples had a survivin-methylated allele, whereas the DMBA-treated cancerous tissues showed no evidence of survivin methylation. The results suggest that survivin may play an important role in DMBA-induced hamster buccal-pouch carcinomas, and that the gene expression may be modulated by an epigenetic mechanism.