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Mnt loss triggers Myc transcription targets, proliferation, apoptosis, and transformation

Jonas A Nilsson1, Kirsteen H Maclean, Ulrich B Keller

  • 1Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.

Molecular and Cellular Biology
|January 30, 2004
PubMed

Insights

Myc antagonists like Mnt normally repress cancer-promoting genes. Mnt knockdown activates these genes, driving cell proliferation and apoptosis, even without Myc, revealing Mnt

Area of Science:

  • Oncogenic signaling pathways
  • Transcriptional regulation in cancer
  • Cell cycle control and apoptosis

Background:

  • Myc oncoproteins are frequently overexpressed in cancers, promoting cell proliferation and transformation.
  • Myc's oncogenic functions, including cell proliferation and apoptosis induction, depend on its role as a transcription factor dimerized with Max.
  • Myc-Max complexes bind to E-boxes in target genes, such as Ornithine decarboxylase (Odc), to regulate their expression.

Purpose of the Study:

  • To investigate the role of Mnt, a putative Myc antagonist, in regulating Myc target genes.
  • To determine if Mnt functions as a tumor suppressor by repressing genes involved in cell proliferation.
  • To elucidate the mechanism by which Myc and Mnt interact to control gene expression and cellular behavior.

Main Methods:

  • Stable retroviral RNA interference (RNAi) was used to knock down Mnt expression.
  • Analysis of gene expression changes in response to Mnt knockdown.
  • Assessment of cell proliferation and apoptosis rates following Mnt knockdown.
  • Fibroblast transformation assays in conjunction with Ras expression.

Main Results:

  • In quiescent cells, Mnt and Max bind to Odc E-boxes, and this complex is displaced by Myc-Max in proliferating cells.
  • Mnt knockdown mimics the "Myc" response, leading to accelerated proliferation and apoptosis.
  • These effects of Mnt knockdown are observed even in cells lacking c-myc.
  • Mnt knockdown, together with Ras, is sufficient to transform primary fibroblasts.

Conclusions:

  • Mnt acts as a tumor suppressor by repressing Myc target genes.
  • Myc functions as an oncogene by relieving Mnt-mediated repression of target genes.
  • Mnt plays a critical role in regulating cell proliferation and apoptosis, independent of c-myc.

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