Cyclin D-cdk6 complex is targeted by p21(WAF) in growth-arrested lymphoma cells

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Updated: Sep 28, 2026

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
12:26

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay

Published on: May 3, 2018

D Tvrdík1, R Djaborkhel, A Nagy

  • 1Laboratory of Gene Expression, 1st Faculty of Medicine, Charles University, Albertov 4, Prague, Czech Republic.

Journal of Structural Biology
|December 20, 2002
PubMed

Insights

Transforming growth factor beta1 (TGFbeta1) inhibits malignant B cell growth by reducing cyclin-dependent kinase (cdk) activity. This involves p21(WAF1) binding to cdk4/cdk6, leading to cell cycle arrest in follicular lymphoma.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Normal B lymphocytes are sensitive to TGFbeta1 growth inhibition.
  • Malignant B lymphoma cells often exhibit resistance to TGFbeta1.
  • Understanding TGFbeta1's mechanism in sensitive lymphoma cells is crucial.

Purpose of the Study:

  • To investigate the molecular mechanisms of TGFbeta1-induced growth arrest in malignant B cells.
  • To examine the role of cyclin-dependent kinases (cdks) and retinoblastoma protein (pRb) phosphorylation.
  • To identify the specific cdk inhibitors involved in TGFbeta1's action.

Main Methods:

  • Treatment of TGFbeta1-sensitive malignant follicular lymphoma cells (DoHH2) with TGFbeta1.
  • Analysis of retinoblastoma protein (pRb) phosphorylation status.
  • Assay of G(1) cyclin-dependent kinase (cdk) activity and complex composition.
  • Western blot analysis for cdk inhibitors.

Main Results:

  • TGFbeta1 significantly reduced the activity of cdk2, cdk4, and cdk6.
  • Hypophosphorylation of pRb at S795 and T373 was observed.
  • cdk4 and cdk6 dissociated from cyclin D, while cyclin E-cdk2 complexes remained intact.
  • TGFbeta1 treatment increased p21(WAF1) binding to cdk4 and cdk6, activating CIP/KIP family inhibitors.

Conclusions:

  • TGFbeta1 induces growth arrest in malignant B cells via inhibition of cdk activity.
  • The mechanism involves pRb hypophosphorylation and increased binding of p21(WAF1) to cdk4/cdk6.
  • Activation of CIP/KIP cdk inhibitors mediates TGFbeta1's anti-proliferative effects in follicular lymphoma.

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