NUPR1 and breast cancer: Because NUPR1 positively regulates the expression of HDAC5, ERBB2, and BIRC5 in both the ER+ luminal A subtype-like and the ERBB2-enrich subtype-like breast cancer cells, targeting NUPR1 or their downstream regulating molecules like HDAC5 and BIRC5 may offer a potential strategy for overcoming resistance to endocrine therapy in patients with ER+ breast cancer (Fig. 6).