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Growth arrest by the LKB1 tumor suppressor: induction of p21(WAF1/CIP1)

Marianne Tiainen1, Kari Vaahtomeri, Antti Ylikorkala

  • 1Haartman Institute and Helsinki University Central Hospital, Biomedicum Helsinki, PO Box 63, 00014 University of Helsinki, Finland.

Human Molecular Genetics
|June 5, 2002
PubMed

Insights

Restoring the LKB1 tumor suppressor gene halts cancer cell growth by inducing a p53-dependent G(1) cell cycle arrest. This mechanism involves the cytoplasmic activity of LKB1, which upregulates the p21 protein.

Area of Science:

  • Molecular Biology
  • Cancer Genetics
  • Cell Cycle Regulation

Background:

  • Germline mutations in the LKB1 tumor suppressor gene cause Peutz-Jeghers syndrome (PJS), increasing cancer risk.
  • LKB1 is a serine/threonine kinase crucial for cellular regulation; its inactivation is linked to PJS.
  • Restoring LKB1 function in cancer cells triggers a G(1) cell cycle arrest.

Purpose of the Study:

  • To elucidate the molecular mechanisms underlying LKB1-mediated G(1) cell cycle arrest.
  • To investigate the role of LKB1 localization and kinase activity in growth suppression.
  • To identify downstream effectors and signaling pathways involved in LKB1's tumor suppressive function.

Main Methods:

  • Expression of wild-type and mutant LKB1 in cancer cell lines.
  • Analysis of LKB1 subcellular localization (cytoplasmic vs. nuclear).
  • Assessment of cell cycle progression, cyclin/CDK activity, and p21(WAF1/CIP1) expression.
  • Investigation of p53 dependency for growth arrest and p21 induction.

Main Results:

  • Active LKB1 localized to both cytoplasm and nucleus; kinase-defective mutants favored the nucleus.
  • Cytoplasmic retention of LKB1, independent of nuclear localization, maintained growth suppression activity kinase-dependently.
  • LKB1-induced G(1) arrest was dependent on p53 and involved upregulation of p21(WAF1/CIP1) via its promoter.
  • Co-expression of Cyclin D1/E bypassed the LKB1-mediated G(1) arrest.

Conclusions:

  • Cytoplasmic LKB1 signaling is critical for mediating growth suppression.
  • The tumor suppressor function of LKB1 involves a p53-dependent induction of p21, leading to G(1) cell cycle arrest.
  • Understanding this pathway offers potential therapeutic strategies targeting LKB1-deficient cancers.

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