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Repression of Myc-Ras cotransformation by Mad is mediated by multiple protein-protein interactions

P J Koskinen1, D E Ayer, R N Eisenman

  • 1Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98104, USA.

Cell Growth & Differentiation : the Molecular Biology Journal of the American Association for Cancer Research
|June 1, 1995
PubMed

Insights

Mad protein antagonizes Myc-induced cell transformation by blocking proliferation. This suggests Mad may function as a tumor suppressor gene by regulating cell growth rather than survival.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Oncology

Background:

  • Mad is a bHLH/Zip protein that heterodimerizes with Max.
  • Mad expression is induced during terminal differentiation.
  • Mad is thought to down-regulate Myc-induced genes driving cell proliferation.

Purpose of the Study:

  • To investigate Mad's role in blocking cellular transformation.
  • To determine the mechanisms by which Mad inhibits Myc-Ras cotransformation.
  • To explore Mad's potential as a tumor suppressor gene.

Main Methods:

  • Transfection of primary rat embryo fibroblasts with c-Myc and c-Ha-Ras oncoproteins.
  • Analysis of Mad mutants lacking specific functional domains.
  • Assessment of Mad's effect on Myc-Ras cotransformation and focus formation.
  • Investigation of the role of Max and mSin3 in Mad-mediated repression.
  • Evaluation of Bcl-2's influence on Mad's effects.

Main Results:

  • Mad blocks transformation of primary rat embryo fibroblasts by c-Myc and c-Ha-Ras.
  • Mad mutants lacking key domains fail to inhibit Myc-Ras cotransformation, indicating DNA-binding and protein interactions are crucial.
  • Repression of cotransformation requires DNA-binding and involves interactions with Max and mSin3.
  • Increasing Myc levels attenuate Mad's inhibitory effects.
  • Mad affects cellular growth properties rather than viability, as demonstrated by Bcl-2 experiments.

Conclusions:

  • Mad antagonizes the biological effects of Myc, inhibiting cell transformation.
  • Mad's repression of transformation is dependent on DNA-binding and interactions with Max and mSin3.
  • Mad's ability to inhibit Myc-Ras cotransformation suggests its potential role as a tumor suppressor gene.

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