SP-RING finger found in protein inhibitor of activated STAT protein 3 (PIAS3) and similar proteins
PIAS3 is an E3 SUMO-protein ligase that was initially identified as an interleukin-6 (IL-6)-dependent repressor of signal transducer and activator of transcription 3 (STAT3) and has anti-proliferative properties. It binds specifically to phosphorylated STAT3 and inhibits its transcriptional activity by blocking its binding to DNA. It regulates STAT3-mediated induction of Snail expression, as well as suppresses acute graft-versus-host disease (GVHD) by modulating effector T and B cell subsets through inhibition of STAT3 activation. It activates the intrinsic apoptotic pathway in non-small cell lung cancer cells independent of p53 status. When overexpressed, it can interact with STAT5 to regulate prolactin-induced STAT5-mediated gene expression. Moreover, PIAS3 binds to and activates Smad3 transcriptional activity, resulting in the enhancement of transforming growth factor-beta (TGF-beta) signaling. It functions as a transcriptional corepressor of Erythroid Kruppel-like factor (EKLF or KLF1) and thus plays an important role in erythropoiesis. It also plays a significant role in DNA damage response (DDR) pathway through promoting homologous recombination (HR)- and non-homologous end joining (NHEJ)-mediated DNA double-strand break (DSB) repair. Furthermore, PIAS3 preferentially interacts with and enhances the SUMOylation of TAK1-binding protein 2 (TAB2), an upstream adaptor protein in the IL-1 signaling pathway. It also promotes SUMOylation and nuclear sequestration of ErbB4 receptor tyrosine kinase. In addition, PIAS3 may form a complex with microphthalmia-associated transcription factor, nuclear factor-kappaB, Smad, and estrogen receptor. Its other transcription factor binding partners include: ETS, EGR1, NR1I2, and GATA1. PIAS3 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.