Miz-1 and Max compete to engage c-Myc: implication for the mechanism of inhibition of c-Myc transcriptional activity by Miz-1

Proteins. 2017 Feb;85(2):199-206. doi: 10.1002/prot.25214. Epub 2016 Dec 23.

Abstract

c-Myc is a basic helix-loop-helix leucine zipper (b-HLH-LZ) transcription factor deregulated in the majority of human cancers. As a heterodimer with Max, another b-HLH-LZ transcription factor, deregulated and persistent c-Myc accumulates at transcriptionally active promoters and enhancers and amplifies transcription. This leads to the so-called transcriptional addiction of tumor cells. Recent studies have showed that c-Myc transcriptional activities can be reversed by its association with Miz-1, a POZ transcription factor containing 13 classical zinc fingers. Although evidences have led to suggest that c-Myc interacts with both Miz-1 and Max to form a ternary repressive complex, earlier evidences also suggest that Miz-1 and Max may compete to engage c-Myc. In such a scenario, the Miz-1/c-Myc complex would be the entity responsible for the inhibition of c-Myc transcriptional amplification. Considering the implications of the Miz-1/c-Myc interaction, it is highly important to solve this duality. While two potential c-Myc interacting domains (hereafter termed MID) have been identified in Miz-1 by yeast two-hybrid, with the b-HLH-LZ as a bait, the biophysical characterization of these interactions has not been reported so far. Here, we report that the MID located between the 12th and 13th zinc finger of Miz-1 and the b-HLH-LZ of Max compete to form a complex with the b-HLH-LZ of c-Myc. Our results support the notion that the repressive action of Miz-1 on c-Myc does not rely on the formation of a ternary complex. The implications of these observations for the mechanism of inhibition of c-Myc transcriptional activity by Miz-1 are discussed. Proteins 2017; 85:199-206. © 2016 Wiley Periodicals, Inc.

Keywords: Max; Miz-1; NMR; b-HLH-LZ; c-Myc; circular dichroism.

MeSH terms

  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / chemistry*
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / genetics
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / metabolism
  • Binding Sites
  • Circular Dichroism
  • Cloning, Molecular
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Gene Expression Regulation
  • Humans
  • Kruppel-Like Transcription Factors / chemistry*
  • Kruppel-Like Transcription Factors / genetics
  • Kruppel-Like Transcription Factors / metabolism
  • Models, Molecular
  • Protein Binding
  • Protein Domains
  • Protein Structure, Secondary
  • Proto-Oncogene Proteins c-myc / chemistry*
  • Proto-Oncogene Proteins c-myc / genetics
  • Proto-Oncogene Proteins c-myc / metabolism
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Signal Transduction
  • Transcription, Genetic

Substances

  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • Kruppel-Like Transcription Factors
  • MAX protein, human
  • Proto-Oncogene Proteins c-myc
  • Recombinant Proteins
  • ZBTB17 protein, human