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The Mad and Myc basic domains are functionally equivalent

Mikhail A Nikiforov1, Nikita Popov, Iulia Kotenko

  • 1Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA.

The Journal of Biological Chemistry
|January 23, 2003
PubMed

Insights

Myc and Mad proteins, crucial for cell growth and cancer, target the same genes. Experiments show that substituting Myc

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • The Myc/Max/Mad family of transcription factors regulates key cellular processes including proliferation, differentiation, and oncogenic transformation.
  • Understanding the specific DNA-binding and functional differences between Myc/Max and Mad/Max heterodimers is crucial for deciphering their roles in normal and cancerous cells.

Purpose of the Study:

  • To investigate whether Myc/Max and Mad/Max heterodimers recognize the same or distinct target genes in vivo.
  • To determine the functional significance of the basic region in Myc/Max/Mad heterodimer specificity and biological activity.

Main Methods:

  • Chromatin immunoprecipitation (ChIP) was employed to identify in vivo DNA binding sites of Myc and Mad1.
  • Site-directed mutagenesis was used to create a chimeric c-Myc protein with the basic region of Mad (c-Myc(Mad-BR)).
  • Comparative analyses of wild-type c-Myc and c-Myc(Mad-BR) were performed for oncogenic transformation, cell proliferation, apoptosis induction, and gene expression activation.

Main Results:

  • Chromatin immunoprecipitation revealed that Myc target genes are also bound by Mad1 in differentiated HL60 cells.
  • The chimeric c-Myc(Mad-BR) protein exhibited indistinguishable biological activity from wild-type c-Myc.
  • Both wild-type c-Myc and the modified c-Myc(Mad-BR) protein demonstrated identical target gene recognition in vivo.

Conclusions:

  • Myc and Mad proteins likely regulate a common set of target genes, suggesting functional overlap.
  • The basic region substitution did not alter the biological activity or target gene recognition of c-Myc, implying this region may not be the sole determinant of heterodimer specificity.

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