We confirmed that the slow migrating form of ERK5 detected in HER2+ breast cancer cell lines disappeared following the suppression of ERK5 activity using the ERK5 inhibitor JWG-045 that exhibits significantly less affinity for BRD4 compared with XMD8–92 (refs. 33, 34; Fig. 2C). The gene discussed is ERBB2; the disease is breast cancer.