Finally, preventing SUMOylation by overexpression of the SENtrin-specific Protease 1 (SENP1) deSUMOylase abolished the difference in transcriptional repression by fulvestrant and OHT in transfected ER-negative cells and in endogenously ER-expressing breast cancer cells (37, 44). The gene discussed is ESR1; the disease is breast carcinoma.