Strategies to Identify and Overcome the Deregulated SUMO-Modification in Endocrine Resistant Breast Cancer
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Resistance to canonical endocrine therapy (ET) remains a major therapeutic challenge for patients of the frequently diagnosed hormone receptor positive (HR+) breast cancer (BCa) subtype. Previous studies show that deregulated Small Ubiquitin Like Modifier (SUMO)-post-translational modification (PTM) of proteins drive breast tumorigenesis. However, if and how the SUMO-proteome changes with chronic treatments of ET is unknown. A collective series of studies demonstrate that androgen receptor (AR) supports resistance to ET and correlates with BCa metastasis. The AR is also a well-known target for SUMO-PTM. Yet, whether AR SUMOylation contributes to the metastatic phenotype of recurrent ET-R BCa remains undefined. Here, we report concurrent accumulation of global SUMOylome and SUMOylated AR in acquired and intrinsic ET-R hormone receptor-positive (HR+) BCa lines. We identified heat shock protein (Hsp27) as a novel SUMO-E3 ligase for AR. Ligand-independent SUMO-AR is chromatin-bound, transcriptionally active, and favors the expression of epithelial-mesenchymal transition genes. Our results show that concurrent targeting of unmodified and SUMO-modified AR is required to attenuate the migration and metastatic phenotype of ET-R BCa. Collectively, we propose increased global SUMOylation and SUMO-modified AR to stratify BCa patients that would benefit from combinatorial treatments of AR antagonists and SUMO inhibitor therapy. High-throughput approaches for rapid screening of SUMO-PTMs are lacking. Also, non-canonical SUMO-acceptor sites and SUMO-interacting motifs (SIM) are a particular hurdle for conventional, laborious biochemical approaches. Here, we apply a microfluidic, peptide-microarray biochip technology (μPepArray™) to rapidly screen for non-covalent and covalent SUMO sites for two challenging protein substrates Hsp27 and core histones, respectively. Using an unbiased screening approach, we identified and confirmed multiple functional SIMs on an established SUMO-E3 ligase Hsp27. Additionally, we designed a unique peptide array to identify several new SUMOylation sites on each of the four core histones. Collectively, we propose μPepArray™ as a rapid screening tool for identifying various forms of SUMO-PTM, applicable for studying SUMO-regulated cellular processes in health and disease.