Functional mimicry of the acetylated C‐terminal tail of p53 by a SUMO‐1 acetylated domain, SAD

Abstract

The ubiquitin-like molecule, SUMO-1, a small protein essential for a variety of biological processes, is covalently conjugated to many intracellular proteins, especially to regulatory components of the transcriptional machinery, such as histones and transcription factors. Sumoylation provides either a stimulatory or an inhibitory signal for proliferation and for transcription, but the molecular mechanisms by which SUMO-1 achieves such versatility of effects are incompletely defined. The tumor suppressor and transcription regulator p53 is a relevant SUMO-1 target. Particularly, the C-terminal tail of p53 undergoes both sumoylation and acetylation. While the effects of sumoylation are still controversial, acetylation modifies p53 interaction with chromatin embedded promoters, and enforces p53 apoptotic activity. In this study, we show that the N-terminal region of SUMO-1 might functionally mimic this activity of the p53 C-terminal tail. We found that this SUMO-1 domain possesses similarity with the C-terminal acetylable p53 tail as well as with acetylable domains of other transcription factors. SUMO-1 is, indeed, acetylated when conjugated to its substrates and to p53. In the acetylable form SUMO-1 tunes the p53 response by modifying p53 transcriptional program, by promoting binding onto selected promoters and by favoring apoptosis. By contrast, when non-acetylable, SUMO-1 enforces cell-cycle arrest and p53 binding to a different sets of genes. These data demonstrate for the first time that SUMO-1, a post-translational modification is, in turn, modified by acetylation. Further, they imply that the pleiotropy of effects by which SUMO-1 influences various cellular outcomes and the activity of p53 depends upon its acetylation state.

Molecular Basis for Phosphorylation-dependent SUMO Recognition by the DNA Repair Protein RAP80

“…Double phosphorylation of the canonical CK2 site in RAP80 substantially elevates the binding affinity for SUMO-2, and suggests a deeper role for CK2 in the repair of double-stranded DNA breaks, at least within the context of RAP80-mediated recruitment of BRCA1 to DNA damage sites. Interestingly, the phosphorylation of SIMs may be cross-regulated through acetylation of Lys 33 in SUMO-2 and Lys 37 in SUMO-1, although additional lysines near the SIM binding cleft may be involved (65)(66)(67). From a structural perspective, Lys 33 and Lys 35 are critical for electrostatic interactions with SIM or phosphorylated SIM; their acetylation abolishes SUMO-SIM binding, although not in all cases.…”

MDM2 promotes SUMO-2/3 modification of p53 to modulate transcriptional activity

“…This result is supported by a microarray performed with a p53-SUMO-1 fusion protein, which showed that only about a third of p53-repressed genes were still repressed by the p53-SUMO fusion. 42 It is possible that sumoylation can modulate the transcriptional activity of p53 by inhibiting p300-mediated acetylation of p53. 41 Although the effects of sumoylation on p53 activity are modest, there are numerous examples of how relatively small changes in p53 activity can have profound effects on physiological outcome.…”

“…41 Further studies suggest that acetylation of SUMO-1 that is conjugated to p53 can also modulate the transcriptional activity of p53. 42 In addition to MDM2, a number of SUMO-E3-ligases that mediate the SUMO-1 conjugation of p53 have been identified, including Topors, 43 the PIAS proteins, 44 TRIM proteins 45 an adenovirus E1B 55-Kilodalton protein. 46 By contrast, relatively few studies have addressed SUMO-2/3 modification of p53.…”

The RAX/PACT-PKR stress response pathway promotes p53 sumoylation and activation, leading to G1arrest

“…28,[32][33][34] Results may potentially be reconciled by the recent finding that phosphorylation or acetylation of SUMO-1 may occur to regulate whether sumoylation can be inhibitory or stimulatory. 36 Thus, sumoylation of p53 may have either an inhibitory or activator function, depending upon whether SUMO-1 has been acetylated and the promoter context or cell type studied. Significantly, our data supports the notion that sumoylation promotes p53 stability, activation and G 1 cell cycle arrest.…”

“…In addition, recent studies indicate that post-translational modification of SUMO-1 may regulate whether sumoylation will inhibit or stimulate p53, with SUMO-1 acetylation activating p53. 35,36 Functionally, it has been proposed that sumoylation of p53 may regulate protein-protein interactions, half-life and/or subcellular localization. 29,37 Now, we report that RAX/PACT, the only identified cellular activator of PKR, can form a complex with p53 and the sumo-conjugating enzyme Ubc9 to induce p53 sumoylation at lysine 386.…”