Disruption of Multiple Overlapping Functions Following Stepwise Inactivation of the Extended Myc Network.

Area of Science:

• Molecular Biology
• Cellular Biology
• Genetics

Background:

• Myc and Mlx are transcription factors regulating cell proliferation, metabolism, and translation.
• They form interconnected networks (Myc Network and Mlx Network) that co-regulate gene expression.
• Understanding their combined roles is crucial for deciphering cellular control mechanisms.

Purpose of the Study:

• To investigate the effects of stepwise inactivation of Myc and Mlx on primary and immortalized murine embryonic fibroblasts (MEFs).
• To determine the role of the Mlx network in Myc-induced growth arrest and senescence.
• To explore the impact on aging, senescence, DNA damage pathways, and genomic stability.

Main Methods:

• Conditional knockout of Myc and Mlx genes in murine embryonic fibroblasts (MEFs).
• Comparison of primary MEFs with SV40 T-antigen immortalized MEFs.
• Analysis of gene expression, cell proliferation, senescence markers, and DNA damage response.

Main Results:

• Myc knockout (MycKO) and Myc × Mlx double knockout (DKO) primary MEFs exhibited rapid growth arrest, aging, and senescence.
• DKO MEFs eventually resumed proliferation, indicating Mlx network's necessity for sustained growth arrest.
• All knockout MEFs showed deregulation of aging, senescence, and DNA damage pathways.
• Immortalized knockout MEFs displayed genomic instability and genotoxic sensitivity.
• DKO MEFs showed selective downregulation of p53 and Rb pathways compared to MycKO MEFs.

Conclusions:

• Durable growth arrest in primary MEFs requires an intact Mlx network.
• Myc and Mlx inactivation broadly impacts aging, senescence, and DNA repair pathways.
• Reversal of Myc-induced growth arrest by Mlx loss or immortalization involves p53 and/or Rb pathway inactivation.