Novel Function of E3 Ubiquitin Ligase Siah2 to Regulate ROS Metabolism

Abstract

The seven in absentia homolog (Siah) family proteins are components of E3 ubiquitin ligase complexes that catalyze the ubiquitination of proteins. Siah proteins target their substrates for proteasomal degradation. Several studies have reported that Siah proteins are involved in tumorigenesis and angiogenesis, particularly through the Ras and HIF-1a signaling pathways in hypoxic response. Recent studies also have reported that Siah2 stabilization impairs the NF-E2-related factor 2 (Nrf2) signaling pathway, which is a master regulator of reactive oxygen species (ROS) metabolism. Hypoxia induces the phosphorylation of Nrf2 and then decreases the Keap1-mediated degradation of Nrf2 compared with that under normoxia. In addition, hypoxia-induced Siah2 provides a dominating Nrf2 degradation pathway over that of Keap1 under hypoxia. Given their critical roles in ROS metabolism, Siah proteins are attractive targets for effective therapy under particular conditions such as hypoxia and hypoglycemia.