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Dominant negative c-jun inhibits activation of the cyclin D1 and cyclin E kinase complexes

R F Hennigan1, P J Stambrook

  • 1Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0521, USA. Robert.Hennigan@uc.edu

Molecular Biology of the Cell
|August 22, 2001
PubMed

Insights

Activating transcription factor 1 (AP-1) regulates cell growth. Inhibiting AP-1 with GFP-TAM67 arrests human fibrosarcoma cells in G1 by increasing p21 expression, impacting cyclin-dependent kinase activity.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cell Cycle Regulation

Background:

  • Activating transcription factor 1 (AP-1) is a crucial transcription factor involved in cell proliferation and cancer development.
  • Oncogenic signaling pathways frequently activate AP-1, highlighting its role in carcinogenesis.

Purpose of the Study:

  • To investigate the specific role of AP-1 in a human fibrosarcoma cell line (HT1080).
  • To elucidate the mechanism by which AP-1 influences cell cycle progression in tumor cells.

Main Methods:

  • Utilized an ecdysone-inducible system to express a dominant-negative c-jun mutant (GFP-TAM67) in HT1080 cells.
  • Assessed AP-1 activity, cell cycle phase distribution, and the expression/activity of key cell cycle regulators (cyclins, CDKs, pRB, p21).

Main Results:

  • High-level expression of GFP-TAM67 inhibited AP-1 activity and induced a reversible G1 cell cycle arrest.
  • Contrary to expectations, GFP-TAM67 did not affect cyclin D1 or cyclin E expression but impaired their kinase activity.
  • GFP-TAM67-induced G1 arrest was associated with hypophosphorylated pRB and increased association of cyclin:cdk complexes with p21(CIP1/WAF1).
  • GFP-TAM67 upregulated p21 mRNA expression, suggesting a role in its induction.

Conclusions:

  • AP-1 plays a novel role in activating G1 cyclin-dependent kinase complexes in human tumor cells.
  • This activation is mediated through the regulation of p21(CIP1/WAF1) gene expression.
  • Targeting AP-1 may offer a therapeutic strategy for fibrosarcoma by modulating cell cycle progression via p21.

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