SP-RING finger found in protein inhibitor of activated STAT protein 4 (PIAS4) and similar proteins
PIAS4, also known as PIASy or protein inhibitor of activated STAT protein gamma (PIAS-gamma), is an E3 SUMO-protein ligase that interacts with the androgen receptor (AR) and is involved in ubiquitin signaling pathways. It is associated with macro/microcephaly in the novel interstitial 19p13.3 microdeletion/microduplication syndrome. It also regulates the hypoxia signalling pathway through interacting with the tumor suppressor von Hippel-Lindau (VHL) and leads to VHL sumoylation, oligomerization, and impaired function during growth of pancreatic cancer cells. Moreover, PIAS4 acts as a direct binding partner for vitamin D receptor (VDR) and facilitates its modification with SUMO2. The process of SUMOylation modulates VDR-mediated signaling. As components of the DNA-damage response (DDR), PIAS4 together with PIAS1 promote responses to DNA double-strand breaks (DSBs). They are required for effective ubiquitin-adduct formation mediated by RNF8, RNF168, and BRCA1 at sites of DNA damage. PIAS4 contains an N-terminal SAP (scaffold attachment factor A/B (SAF-A/B), acinus and PIAS) box with the LXXLL signature, a PINT motif, a specific RING finger known as Siz/PIAS (protein inhibitor of activated signal transducer and activator of transcription) RING (SP-RING) finger, and the acidic C-terminal domain.