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A second protein kinase CK1-mediated step negatively regulates Wnt signalling by disrupting the lymphocyte enhancer

A Hämmerlein1, J Weiske, O Huber

  • 1ABDA - Federal Union of German Associations of Pharmacists, Jägerstr. 49/50, 10117, Berlin, Germany.

Cellular and Molecular Life Sciences : CMLS
|March 5, 2005
PubMed

Insights

Casein kinase 1 (CK1) and CK2 directly phosphorylate LEF-1, impacting Wnt signaling. CK1 inhibits LEF-1/beta-catenin transcription, acting as a tumor suppressor.

Area of Science:

  • Molecular Biology
  • Cellular Signaling
  • Cancer Research

Background:

  • The Wnt signaling pathway is crucial for development and is frequently dysregulated in cancer.
  • Aberrant activation of Wnt signaling leads to beta-catenin stabilization and uncontrolled transcription of target genes.
  • Phosphorylation of key pathway components by kinases like CK1 and CK2 regulates beta-catenin stability and activity.

Purpose of the Study:

  • To investigate the direct interaction and phosphorylation of Lymphocyte Enhancer Factor-1 (LEF-1) by CK1 and CK2.
  • To elucidate the functional consequences of CK1 and CK2 mediated phosphorylation on the LEF-1/DNA and LEF-1/beta-catenin complexes.
  • To determine the role of CK1 and CK2 in regulating Wnt target gene transcription and their implications in cancer.

Main Methods:

  • In vitro kinase assays to assess direct binding and phosphorylation of LEF-1 by CK1 and CK2.
  • Electrophoretic mobility shift assays (EMSAs) to analyze changes in LEF-1/DNA complex formation.
  • Co-immunoprecipitation assays to study the interaction between LEF-1 and beta-catenin.
  • Reporter gene assays to quantify LEF-1/beta-catenin transcriptional activity.

Main Results:

  • CK1 and CK2 directly bind and phosphorylate LEF-1, inducing distinct changes in LEF-1/DNA binding.
  • CK1 phosphorylation disrupts the LEF-1/beta-catenin complex without affecting LEF-1 DNA binding.
  • CK1-dependent phosphorylation inhibits LEF-1/beta-catenin transcriptional activity, while CK2 activates it.
  • Efficient disruption of the LEF-1/beta-catenin complex requires sequential phosphorylation of both LEF-1 and beta-catenin.

Conclusions:

  • CK1 acts as a negative regulator of Wnt signaling by inhibiting LEF-1/beta-catenin transcriptional activity.
  • CK1 functions at a second level, beyond the beta-catenin destruction complex, to control Wnt-mediated transcription.
  • These findings highlight CK1's role in suppressing Wnt-driven carcinogenesis by modulating the LEF-1/beta-catenin transcription complex.

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