Abstract
Abstract Epigenetic reprogramming allows breast cancer (BCa) cells to bypass normal growth checkpoints and acquire an aggressive morphology. Function of critical epigenetic proteins is directed by small ubiquitin-like modifiers (SUMO) posttranslational modification (PTM). Components of the SUMO system are dysregulated in BCa. Our objective is to delineate how changes to SUMO-PTM affect epigenetic programs that coordinate BCa pathology. We report that chromatin-bound SUMO protease SENP7L is upregulated in metastatic tamoxifen-resistant (TamR) and triple-negative BCa. SENP7L facilitates chromatin remodeling that potentiates the growth and invasiveness of these BCa subtypes. SENP7L interacts with and deSUMOylates heterochromatin protein 1 alpha (HP1-alpha/CBX5) to mediates these responses. Canonical models suggest that HP1-alpha reads the histone mark to localize predominantly at constitutive heterochromatin. Our studies challenge the old paradigm as we show that SUMOylated HP1-alpha is enriched outside heterochromatin at euchromatin, including E2F-responsive and mesenchymal gene loci. Recruitment of SUMOylated HP1-alpha supports de novo heterochromatin formation at these loci. However, SUMOylated HP1-alpha is lost in aggressive BCa due to SENP7L induction. Consistently, SENP7L upregulation prompts chromatin de-condensation and gene transcription. Nuclei acid and chemical targeting of SENP7L reduces self-renewal/differentiation properties of TamR mammospheres as well as tumor volume and secondary tumor formation of TamR cells. Hence, SENP7L inhibitors can serve as promising tools to modulate epigenetic abnormalities in TamR BCa. Citation Format: Bawa-Khalfe T, Kumar S, Lin F-M. SUMO wrestles breast cancer: SUMO posttranslational modification directs breast cancer cell epigenome. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-04-03.
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