Estrogen receptor (ER)-negative breast cancer is thought to be more malignant and devastating than ER-positive breast cancer and exhibit elevated NF-κB activity. How abnormally high NF-κB activity is maintained in ER-negative breast cancer is poorly understood. The importance of linear ubiquitination, which is generated by the linear ubiquitin chain assembly complex (LUBAC), is increasingly appreciated in NF-κB signaling, which regulates cell activation and death. Here, we showed that epsin proteins, a family of ubiquitin-binding endocytic adaptors, interacted with LUBAC via its Ubiquitin-Interacting Motif (UIM) and bound LUBAC’s bona fide substrate NEMO via its N-terminal homolog (ENTH) domain. Furthermore, epsins promoted NF-κB essential modulator (NEMO) linear ubiquitination and served as scaffolds for recruiting other components of the IκB kinase (IKK) complex; thereby, resulting in the heightened IKK activation and sustained NF-κB signaling essential for the development of ER-negative breast cancer. Heightened epsin levels in ER-negative human breast cancer are associated with poor, relapse-free survival. We showed that transgenic and pharmacological approaches eliminating epsins potently impeded breast cancer development in both spontaneous and patient-derived xenograft breast cancer mouse models. Our findings established the pivotal role epsins played in promoting breast cancer. Thus, targeting epsins may represent a strategy to restrain NF-κB signaling, and provide an important perspective into ER-negative breast cancer treatment.
Kai Song, Xiaofeng Cai, Yunzhou Dong, Hao Wu, Yong Wei, Uma Shankavaram, Kui Cui, Yang Lee, Bo Zhu, Sudarshan Bhattacharjee, Beibei Wang, Kun Zhang, Aiyun Wen, Scott Wong, Lili Yu, Lijun Xia, Alana L Welm, Diane R. Bielenberg, Kevin Camphausen, Yibin Kang, Hong Chen