Abstract
Purpose: Inactivation of PTEN has been reported in many human and mouse tumors. DNA methylation in non-small cell lung cancer and DNA mutations in endometrial carcinomas, glioblastomas and Cowden disease are frequently reported. Based on reduced expression and frequent loss of heterozygosity (LOH) at Pten locus, epigenetic inactivation of Pten has been suggested in radiation-induced mouse thymic lymphomas (TLs). In this study, we have examined the epigenetic and genetic alteration of Pten in TLs.
Materials and methods: The 4-week-old female B6C3F1 mice were exposed weekly to 2.0Gy whole-body X irradiation for 4 consecutive weeks and monitored daily until moribund, and then autopsied. First, DNA extracted from TLs was typed using microsatellite markers for the identification of LOH. Then, we examined expression of Pten by RT-PCR and pattern of DNA methylation by bisulfite sequencing.
Results/Conclusion: Pten is mapped on the 24.5cM region from centromere of mouse chromosome 19. LOH was frequently found (6/23, 26%) at this region. TLs showed reduced expression (12/23, 52%) or transcriptionally silencing of Pten (1/23, 4%). However, no aberrant DNA methylation was detected in a CpG island of untranslated Exon 1 and its 5' upstream region. The present results suggest that DNA methylation did not contribute to transcriptional silencing of Pten in TLs. One TL showed aberrant splicing of Pten, which has not been reported so far. In a search for point mutations in the Pten coding region, the RT-PCR products from the others are currently being sequenced.
