RNF115/BCA2 E3 Ubiquitin Ligase Promotes Breast Cancer Cell Proliferation through Targeting p21Waf1/Cip1 for Ubiquitin-Mediated Degradation

The E3 ubiquitin ligase RING finger protein 115 (RNF115), also known as breast cancer-associated gene 2 (BCA2), has previously been reported to be overexpressed in estrogen receptor alpha (ER alpha)-positive breast tumors and to promote breast cell proliferation; however, its mechanism is unknown. In this study, we demonstrated that silencing of BCA2 by small interfering RNAs (siRNAs) in two ER alpha-positive breast cancer cell lines, MCF-7 and T47D, decreases cell proliferation and increases the protein levels of the cyclin-dependent kinase inhibitor p21(Waf/Cip1). The protein stability of p21 was negatively regulated by BCA2. BCA2 directly interacts with p21 and promotes p21 ubiquitination and proteasomal degradation. Knockdown of p21 partially rescues the cell growth arrest induced by the BCA2 siRNA. These results suggest that BCA2 promotes ER alpha-positive breast cancer cell proliferation at least partially through downregulating the expression of p21.