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Interleukin-2-mediated elimination of the p27Kip1 cyclin-dependent kinase inhibitor prevented by rapamycin

J Nourse1, E Firpo, W M Flanagan

  • 1Program in Cancer Biology, Stanford University Medical School, California 94305.

Nature
|December 8, 1994
PubMed

Insights

Interleukin-2 (IL-2) signaling enables cyclin-dependent kinase (Cdk) activation by reducing p27Kip1 levels, a process blocked by rapamycin, revealing p27Kip1

Area of Science:

  • Cell Biology
  • Immunology
  • Molecular Biology

Background:

  • Cyclin-dependent kinases (Cdks) complexed with G1 cyclins (D and E) regulate the rate-limiting step for entry into S phase.
  • T-cell activation involves antigen-receptor signaling promoting cyclin E and Cdk2 synthesis, while interleukin-2 (IL-2) signaling activates these complexes.
  • Rapamycin is an immunosuppressant that inhibits G1-to-S phase progression and causes cell-cycle arrest.

Purpose of the Study:

  • To investigate the mechanism by which IL-2 signaling activates Cdk complexes in T lymphocytes.
  • To determine the role of rapamycin in modulating IL-2-mediated Cdk activation.
  • To elucidate the specific roles of Cdk inhibitor proteins p27Kip1 and p21 in T-cell cycle progression.

Main Methods:

  • Analysis of Cdk activation in T lymphocytes.
  • Investigation of cyclin E/Cdk2 complex formation and activity.
  • Assessment of Cdk inhibitor protein (p27Kip1 and p21) levels and their regulation by IL-2 and rapamycin.

Main Results:

  • IL-2 signaling promotes Cdk activation by inducing the degradation of the Cdk inhibitor p27Kip1.
  • Rapamycin inhibits IL-2-mediated Cdk activation by preventing the elimination of p27Kip1.
  • IL-2 induces the expression of the Cdk inhibitor p21, an effect that is blocked by rapamycin.

Conclusions:

  • p27Kip1 is a key regulator of Cdk activity during the G1-to-S phase transition in quiescent T lymphocytes.
  • IL-2 signaling overcomes p27Kip1-mediated inhibition, facilitating cell cycle entry.
  • The function of p21 may be confined to actively cycling cells, distinct from p27Kip1's role in quiescence exit.

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