Activation of p53 by Protein Inhibitor of Activated Stat1 (PIAS1)

Abstract

The tumor suppressor protein p53 functions as a transcriptional factor that activates genes controlling cell cycle arrest and apoptosis. Here, we report that protein inhibitor of activated Stat1 (PIAS1) interacts with the tetramerization and C-terminal regulatory domains of p53 in yeast two-hybrid analyses. Endogenous PIAS1 is also associated with endogenous p53 in mammalian cells. Ectopic expression of PIAS1 activates p53-mediated expression in mouse embryonic fibroblast cells (p53 ؊/؊ ) as well as a variety of other cell lines. Furthermore, ectopic expression of PIAS1 induces p53-mediated expression of cyclin-dependent kinase inhibitor p21 and G 1 arrest of the cell cycle in H1299 cells. In addition, a PIAS1 mutant without the RING-finger domain required for sumoylation could still activate p53-mediated gene expression, indicating that activation of p53 by PIAS1 does not require the RING-finger domain. Taken together, our results suggest that PIAS1 is a novel activator of p53.The tumor suppressor protein p53 is normally very short-lived and remains at very low levels through proteasomal degradation in unstressed mammalian cells. In response to damaged DNA, nucleotide depletion, hypoxia, oncogenes, and other genotoxic stresses, p53 accumulates dramatically in nucleus and functions as a transcriptional activator (1-4). Activation of p53 leads to cell cycle arrest or apoptosis by inducing a number of genes including cyclin-dependent kinase inhibitor p21 and apoptotic genes such as Bax. Although the exact mechanisms by which some of these stress signals are transduced to p53 are not known, signaling to p53 is thought to be mediated by upstream p53 regulators in at least three distinguishable pathways (5). The first pathway transduces signals of DNA damage induced by ionizing radiation, which activates ATM, Chk2, and subsequently p53. The second pathway is mediated by p14 ARF -MDM2 interaction (6), which is triggered by oncogenic signals such as Ras and Myc. The third pathway is turned on by a wide array of chemotherapeutic drugs, UV light, and protein kinase inhibitors, which requires kinases ATR and casein kinase II. There are additional proteins that can activate p53, but the significance of some of these interactions remains to be elucidated (1).The key negative regulator of the p53 network is MDM2. Transcription of MDM2 is itself activated by p53. However, MDM2 protein can both inhibit the transcriptional activity of p53 and target p53 for ubiquitin-mediated protein degradation (7-9), forming a negative regulatory loop for p53 function. Interference of the p53 and MDM2 interaction appears to be a main convergent point for many of the stress signals, resulting in stabilization and activation of p53 (10).The discovery of p63 and p73, the p53 family members, added a new level of complexity to understanding the p53 network (11). Both p63 and p73 produce multiple transcripts, which could either activate or inhibit p53-mediated gene expression. In contrast to p53, p63 and p73 do not interact with most viral proteins...

PIAS1 and PIASxα Function as SUMO-E3 Ligases toward Androgen Receptor and Repress Androgen Receptor-dependent Transcription

“…Similarly, RING finger-like domain mutant PIASx␤ slightly induced the transactivation of p53, although wild-type PIASx␤ repressed the transcriptional activity of p53 (30). In contrast, another group reported that PIAS1 stimulated p53-dependent transcriptional activation and that a PIAS1 mutant lacking the RING finger-like domain also activated p53-mediated gene expression as efficiently as did the wild-type (34). These findings suggest that the RING finger-like domain of PIAS proteins may not only play a role in the sumoylation of substrates but also in another function, such as protein-protein or protein-DNA interaction.…”

Sumoylation of the net inhibitory domain (NID) is stimulated by PIAS1 and has a negative effect on the transcriptional activity of Net

“…Furthermore, PIAS proteins interact with other factors associated with repression of transcription, including the nuclear matrix (Sachdev et al, 2001;Tan et al, 2002) and HDACs (Tussie-Luna et al, 2002;Long et al, 2003). Sumoylation alone is not sufficient to account for repression by PIAS proteins (Sachdev et al, 2001;Megidish et al, 2002;Schmidt and Muller, 2002). However, SUMO fused to a heterologous DNA-binding domain can repress transcription (Iniguez-Lluhi and Pearce, 2000; Kim et al, 2002;Ross et al, 2002;Yang et al, 2002), suggesting that SUMO itself mediates at least part of the transcriptional effect.…”

SUMO: a regulator of gene expression and genome integrity

“…Hence, replacement of lysine 386 to arginine correlates with an activation of p53-mediated transactivation in reporter gene assays. Moreover, expression of a SUMO-isopeptidase, which cleaves SUMO from p53, stimulates p53 transactivation (Chen and Chen, 2003), while overexpression of PIAS proteins, which induce p53 SUMOylation, is accompanied by either an up-or downregulation of p53 activity (Nelson et al, 2001;Megidish et al, 2002;Schmidt and Muller, 2002;Wible et al, 2002). These later effects, however, are only partially linked to altered SUMO-modification of p53, because they are at least independent of lysine 386 SUMOylation.…”