Abstract 406: A potential new mechanism for PTEN to maintain genome stability

Abstract Purpose: PTEN (phosphatase and tensin homolog) is among the most mutated or lost tumor suppressors. Recent studies revealed that nuclear PTEN represses tumorigenesis by stabilizing the centromere, a highly condensed heterochromatin domain featured with long array of DNA repeats (namely, satellite DNA), repressive histones, such as trimethylated Histone H3 at Lys9 residue (H3K9me3), and heterochromatin proteins. Our studies are aimed to explore the molecular mechanism that PTEN regulates this heterochromatin structure and thus maintaining genome stability. Methods and Results: Co-immunoprecipitation (Co-IP) assay showed that PTEN and the heterochromatin proteins directly interact. Chromatin immunoprecipitation (ChIP) assay showed that PTEN is enriched in satellite locus. Depletion of PTEN leads to abnormal heterochromatin structure, indicated by reduced H3K9m3 foci (detected by immunofluorescent staining) and occupancy to satellite locus (ChIP assay), decreased heterochromatin protein levels (Westernblot analysis), and overexpression of satellite transcripts (quantitative RT-PCR). Through a knockdown-and-mutant rescue strategy, we found that the C-terminal of PTEN is essential for its repressive function on satellite transcription. Furthermore, overexpression of the C-terminal truncated PTEN into PTEN-null BT549 cells, as compared to wild-type PTEN overexpression, lost its function to suppress cell growth (MTT assay), cell cycle progression (flow cytometry analysis) and protection from DNA damage (MTT and colony formation assays). Conclusions: Our finding showed that PTEN guards the genome stability through maintaining the normal structure of heterochromatin domain. Citation Format: Lili Gong, Shiaw-Yih Lin. A potential new mechanism for PTEN to maintain genome stability. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 406. doi:10.1158/1538-7445.AM2014-406