RNF4 is a poly-SUMO-specific E3 ubiquitin ligase required for arsenic-induced PML degradation

Abstract

In acute promyelocytic leukaemia (APL), the promyelocytic leukaemia (PML) protein is fused to the retinoic acid receptor alpha (RAR). This disease can be treated effectively with arsenic, which induces PML modification by small ubiquitin-like modifiers (SUMO) and proteasomal degradation. Here we demonstrate that the RING-domain-containing ubiquitin E3 ligase, RNF4 (also known as SNURF), targets poly-SUMO-modified proteins for degradation mediated by ubiquitin. RNF4 depletion or proteasome inhibition led to accumulation of mixed, polyubiquitinated, poly-SUMO chains. PML protein accumulated in RNF4-depleted cells and was ubiquitinated by RNF4 in a SUMO-dependent fashion in vitro. In the absence of RNF4, arsenic failed to induce degradation of PML and SUMO-modified PML accumulated in the nucleus. These results demonstrate that poly-SUMO chains can act as discrete signals from mono-SUMOylation, in this case targeting a poly-SUMOylated substrate for ubiquitin-mediated proteolysis.

SUMOylation Affects the Interferon Blocking Activity of the Influenza A Nonstructural Protein NS1 without Affecting Its Stability or Cellular Localization

“…As SUMO chains are associated exclusively with SUMO2/3 conjugation, this observation indicates that NS1 is likely preferentially SUMOylated by SUMO2/3. SUMO2/3 chains are known to stimulate the polyubiquitination of some SUMOylated proteins, therefore triggering their proteasomal degradation (71)(72)(73)(74). However, our data indicate that SUMOylation does not affect the stability of NS1 (see below).…”

“…Importantly, for certain substrates, SUMOylation with SUMO2/3 is known to trigger the formation of long poly-SUMO chains that are recognized by ubiquitin ligases and lead to the polyubiquitinylation of the SUMOylated substrate, which in turns leads to their proteasomal degradation (71)(72)(73)(74). Data obtained during the execution of these studies revealed the formation of polySUMOylated NS1 in the presence of wt-ASL and mut-ASL (see, for example, Fig.…”

Nuclear organization in genome stability: SUMO connections

“…Although different types of stress trigger increases in global SUMO conjugation levels, arsenic very specifically triggers sumoylation of PML (or the PML-RARα fusion). Recent work confirmed that the modified PML then becomes an in vivo target of the STUbL RNF4 [96][97][98][99]. Specifically, ATO-induced PML sumoylation correlates with its subsequent K48-linked polyubiquitination and degradation by the proteasome [100].…”

Identification of a molecular recognition feature in the E1A oncoprotein that binds the SUMO conjugase UBC9 and likely interferes with polySUMOylation

“…In addition, SUMO-targeted ubiquitin ligases recognize SUMOylated proteins and polyubiquitylate them, targeting them for degradation (Prudden et al, 2007;Sun et al, 2007;Xie et al, 2007;Mullen and Brill, 2008;Weisshaar et al, 2008). Interestingly, PML is the only protein in mammalian cells identified so far that is targeted by the RNF4 SUMOtargeted ubiquitin ligases (Lallemand-Breitenbach et al, 2008;Tatham et al, 2008), and E1A had an observable effect on PML localization that was specifically dependent on binding UBC9 (Figure 6). …”