RING finger, HC subclass, found in seven in absentia homolog 2 (SIAH2) and similar proteins
SIAH2 is an E3 ubiquitin-protein ligase that contributes to proteasome-mediated degradation of multiple targets in numerous cellular processes. It targets the ubiquitylation and degradation of tumor necrosis factor receptor-associated factor 2 (TRAF2) under stress conditions, which is required for the cell to commit to undergoing apoptosis. It is, therefore, a key regulator of TRAF2-dependent signaling in response to tumor necrosis factor-alpha (TNF-alpha) treatment and UV irradiation. SIAH2 modulates the polyubiquitination of G protein pathway suppressor 2 (GPS2), and targets it for proteasomal degradation. It is also a regulator of NF-E2-related factor 2 (Nrf2), a key regulator of cellular oxidative response, and contributes to the degradation of Nrf2 irrespective of its phosphorylation status. Moreover, SIAH2 contributes to castration-resistant prostate cancer (CRPC) by regulation of androgen receptor (AR) transcriptional activity. It enhances AR transcriptional activity and prostate cancer cell growth. Its stability can be regulated by AKR1C3. SIAH2 also inhibits tyrosine kinase-2 (TYK2)-STAT3 signaling in lung carcinoma cells. Furthermore, SIAH2 regulates obesity-induced adipose tissue inflammation by altering peroxisome proliferator-activated receptor gamma (PPAR gamma) protein levels and selectively regulating PPAR gamma activity. It also functions as a regulator of the nuclear hormone receptor RevErbalpha (Nr1d1) stability and rhythmicity, and overall circadian oscillator function. In addition, SIAH2 is an essential component of the hypoxia response Hippo signaling pathway and has been implicated in normal development and tumorigenesis. It modulates the hypoxia pathway upstream of hypoxia-induced transcription factor subunit HIF-1alpha, and therefore may play an important role in angiogenesis in response to hypoxic stress in endothelial cells. It also stimulates transcriptional coactivator YAP1 by destabilizing serine/threonine-protein kinase LATS2, a critical component of the Hippo pathway, in response to hypoxia. Meanwhile, SIAH2 is involved in regulation of tight junction integrity and cell polarity under hypoxia, through its regulation of apoptosis-stimulating proteins of p53 subunit 2 (ASPP2) stability. SIAH2 contains an N-terminal C3HC4-type RING-HC finger, two zinc-finger subdomains, and a C-terminal tumor necrosis factor (TNF) receptor associated factor (TRAF)-like substrate-binding domain (SBD) responsible for dimer formation.
Comment:C3HC4-type RING-HC finger consensus motif: C-X2-C-X(9-39)-C-X(1-3)-H-X(2-3)-C-X2-C-X(4-48)-C-X2-C, where X is any amino acid and the number of X residues varies in different fingers
Comment:A RING finger typically binds two zinc atoms, with its Cys and/or His side chains in a unique "cross-brace" arrangement.
Jiyao W et al.(2023). "The conserved domain database in 2023.",