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Activated Raf-1 causes growth arrest in human small cell lung cancer cells

R K Ravi1, E Weber, M McMahon

  • 1The Oncology Center, The Johns Hopkins University Medical Institutions, Baltimore, Maryland 21287, USA.

The Journal of Clinical Investigation
|February 14, 1998
PubMed

Insights

Activating the raf/MEK/mitogen-activated protein kinase (MAPK) pathway in small cell lung cancer (SCLC) cells suppressed growth and induced cell cycle arrest. This suggests targeting MAPK pathway activation could be a novel therapeutic strategy for SCLC.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cell Biology

Background:

  • Small cell lung cancer (SCLC) is an aggressive form of lung cancer with poor prognosis.
  • Unlike other lung cancers, SCLC lacks ras mutations, suggesting unique signaling pathway involvement.
  • The raf-MEK-MAPK pathway is a key signaling cascade implicated in cancer cell proliferation.

Purpose of the Study:

  • To investigate the biological effects of activating the raf-MEK-MAPK pathway in SCLC cells.
  • To determine if MAPK pathway activation influences SCLC cell growth, cell cycle, and key regulatory proteins.
  • To explore the therapeutic potential of targeting MAPK pathway activation in SCLC.

Main Methods:

  • Transfection of SCLC cell lines (NCI-H209, NCI-H510) with a fusion gene (DeltaRaf-1:ER) to enable inducible Raf-1 activation.
  • Assessment of MAPK phosphorylation levels following DeltaRaf-1:ER activation.
  • Evaluation of cellular proliferation, soft agar cloning ability, and cell cycle distribution.
  • Analysis of cyclin-dependent kinase (cdk) inhibitor p27(kip1) expression and cdk2 kinase activity.
  • Inhibition studies using the MEK inhibitor PD098059.

Main Results:

  • Activation of DeltaRaf-1:ER led to robust MAPK phosphorylation in SCLC cells.
  • MAPK pathway activation significantly suppressed growth capacity and soft agar cloning ability.
  • Cell cycle analysis revealed cell accumulation in G1 and G2 phases with S phase depletion.
  • Raf activation induced a marked increase in p27(kip1) levels and decreased cdk2 kinase activity.
  • The observed effects were reversible by pretreatment with the MEK inhibitor PD098059.

Conclusions:

  • MAPK pathway activation by DeltaRaf-1:ER induces potent growth inhibitory signals and cell cycle arrest in SCLC.
  • The raf/MEK/MAPK pathway, when activated, leads to cell cycle arrest through mechanisms involving p27(kip1) and cdk2.
  • Targeting MAPK pathway activation, rather than inhibition, may represent a novel therapeutic strategy for SCLC and other neuroendocrine tumors.

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