A non-covalent interaction between small ubiquitin-like modifier-1 and Zac1 regulates Zac1 cellular functions

Int J Biochem Cell Biol. 2012 Mar;44(3):547-55. doi: 10.1016/j.biocel.2011.12.012. Epub 2011 Dec 27.

Abstract

Zac1, a zinc-finger protein that regulates apoptosis and cell cycle arrest 1, such as p53, can induce cell-cycle arrest and apoptosis. The transactivation and coactivation functions of Zac1 may occur at non-promyelocytic leukemia nuclear body (PML-NB) sites in the presence of other PML-NB components, including ubiquitin-conjugating 9 (Ubc9). It is unclear whether post-translational modification of Zac1 by the small ubiquitin-like modifier SUMO plays a role in the coactivation functions of Zac1 for the regulation of the p21 gene. Mutagenesis experiments revealed that the two SUMO-binding lysine residues of Zac1, K237 and K424, repress the transactivation activity of Zac1. Studies using a SUMO-1 C-terminal di-glycine motif mutant that is deficient in the ability to form covalent bonds with lysines, SUMO-1 (GA), and a dominant-negative Ubc9 construct (C93S) indicated that SUMO-1 might regulate Zac1 transactivation and coactivation via a non-covalent interaction. Unlike the wild-type Zac1, which induced apoptosis, the Zac1 (K237/424R) double mutant had the ability to induce autophagy. The functional role of p21 remains to be investigated. SUMO-1 selectively suppressed the induction of the p21 gene and protein by wild-type Zac1 but not by the Zac1 (K237/424R) double mutant. Moreover, wild-type Ubc9 but not Ubc9 (C93S) further potentiated the suppression of SUMO-1 in all Zac1-induced p21 promoter activities. Our data reveal that p21 may be an important factor for the prevention of Zac1-induced apoptosis without affecting autophagosome formation. This work indicates that Zac1 functions are regulated, at least in part, via non-covalent interactions with SUMO-1 for the induction of p21, which is important for the modulation of apoptosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / genetics*
  • Autophagy
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics*
  • Gene Expression Regulation*
  • HeLa Cells
  • Humans
  • Mutagenesis, Site-Directed
  • Mutation / genetics
  • Protein Binding / genetics
  • Protein Interaction Domains and Motifs / genetics
  • Protein Processing, Post-Translational
  • SUMO-1 Protein / genetics
  • SUMO-1 Protein / metabolism*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcriptional Activation / genetics
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism*
  • Ubiquitin-Conjugating Enzymes / genetics
  • Ubiquitin-Conjugating Enzymes / metabolism

Substances

  • CDKN1A protein, human
  • Cell Cycle Proteins
  • Cyclin-Dependent Kinase Inhibitor p21
  • PLAGL1 protein, human
  • SUMO-1 Protein
  • Transcription Factors
  • Tumor Suppressor Proteins
  • Ubiquitin-Conjugating Enzymes
  • ubiquitin-conjugating enzyme UBC9