title: SAG/RBX2 is a novel substrate of NEDD4-1 E3 ubiquitin ligase and mediates NEDD4-1 induced chemosensitization.
abstract: Sensitive to apoptosis gene (SAG), also known as RBX2, ROC2, or RNF7, is a RING component of SCF E3 ubiquitin ligases, which regulates cellular functions through ubiquitylation and degradation of many protein substrates. Although our previous studies showed that SAG is transcriptionally induced by redox, mitogen and hypoxia via AP-1 and HIF-1, it is completely unknown whether and how SAG is ubiquitylated and degraded. Here we report that NEDD4-1, a HECT domain-containing E3 ubiquitin ligase, binds via its HECT domain directly with SAG's C-terminal RING domain and ubiquitylates SAG for proteasome-mediated degradation. Consistently, SAG protein half-life is shortened or extended by NEDD4-1 overexpression or silencing, respectively. We also found that SAG bridges NEDD4-1 via its C-terminus and CUL-5 via its N-terminus to form a NEDD4-1/SAG/CUL-5 tri-complex. Biologically, NEDD4-1 overexpression sensitizes cancer cells to etoposide-induced apoptosis by reducing SAG levels through targeted degradation. Thus, SAG is added to a growing list of NEDD4-1 substrates and mediates its biological function.
authors.affiliation: Division of Radiation and Cancer Biology, Department of Radiation Oncology, University of Michigan, Ann Arbor, MI.
authors.forename: Weihua
authors.initials: W
authors.lastname: Zhou
authors.affiliation: Division of Radiation and Cancer Biology, Department of Radiation Oncology, University of Michigan, Ann Arbor, MI.
authors.forename: Jie
authors.initials: J
authors.lastname: Xu
authors.affiliation: Division of Radiation and Cancer Biology, Department of Radiation Oncology, University of Michigan, Ann Arbor, MI.
authors.forename: Yongchao
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Division of Radiation and Cancer Biology, Department of Radiation Oncology, University of Michigan, Ann Arbor, MI. Institute of Translational Medicine, Zhejiang University School of Medicine, Hangzhou, Zhejiang, P.R. China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D044842:Cullin Proteins / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D005047:Etoposide / Q000494:pharmacology*; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D000075702:Nedd4 Ubiquitin Protein Ligases; D017434:Protein Structure, Tertiary; D014162:Transfection; D044767:Ubiquitin-Protein Ligases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D000972:Antineoplastic Agents, Phytogenic; C496871:CUL5 protein, human; D044842:Cullin Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D005047:Etoposide; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618483:Nedd4 protein, human; C118307:RNF7 protein, human; D044767:Ubiquitin-Protein Ligases