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Contact inhibition and high cell density deactivate the mammalian target of rapamycin pathway, thus suppressing the

Olga V Leontieva1, Zoya N Demidenko1, Mikhail V Blagosklonny2

  • 1Department of Cell Stress Biology, Roswell Park Cancer Institute, Buffalo, NY 14263.

Proceedings of the National Academy of Sciences of the United States of America
|June 4, 2014
PubMed

Insights

Contact inhibition (CI) prevents cells from entering senescence by inhibiting the mammalian target of rapamycin (mTOR) pathway. This explains why cells avoid senescence in vivo and why CI is reversible.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Contact inhibition (CI) causes cell cycle arrest but not senescence, allowing cells to proliferate upon replating.
  • The mechanism by which cells avoid senescence during CI is not fully understood.
  • Senescence entry (geroconversion) is known to be regulated by mammalian target of rapamycin (mTOR) and can be suppressed by inhibiting mTOR.

Purpose of the Study:

  • To investigate the mechanism of senescence avoidance during contact inhibition (CI).
  • To determine the role of the mammalian target of rapamycin (mTOR) pathway in CI-induced senescence evasion.
  • To identify factors contributing to mTOR inhibition in high cell density conditions.

Main Methods:

  • Assessed p27 induction as a marker for CI in normal cells.
  • Investigated the association between CI and mTOR pathway activity.
  • Examined the effect of mTOR stimulation on senescence in contact-inhibited cells.
  • Studied mTOR inhibition and senescence in cancer cells under confluent conditions.
  • Evaluated the impact of normal cells on cancer cell senescence.

Main Results:

  • Contact inhibition (CI) in normal cells, marked by p27 induction, correlated with mTOR pathway inhibition.
  • CI counteracted senescence induced by CDK inhibitors, and mTOR stimulation promoted senescence in CI cells.
  • In cancer cells, confluent culture led to mTOR inhibition via medium conditioning, suppressing p21-induced senescence.
  • Malignant cells co-cultured with contact-inhibited normal cells also showed suppressed p21-induced senescence.

Conclusions:

  • Two key mechanisms inhibit mTOR at high cell density: CI with p27 induction (normal cells) and medium conditioning (especially cancer cells).
  • These mechanisms explain the reversibility of CI and how cells evade senescence in vivo.
  • Understanding these pathways is crucial for cancer research and therapeutic development.

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