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Cbl-b mediates TGFβ sensitivity by downregulating inhibitory SMAD7 in primary T cells

Thomas Gruber1, Reinhard Hinterleitner, Natascha Hermann-Kleiter

  • 1Department for Pharmacology and Genetics, Medical University of Innsbruck, Innsbruck, Austria.

Journal of Molecular Cell Biology
|May 28, 2013
PubMed

Insights

The E3 ligase Cbl-b controls T cell responses to transforming growth factor beta (TGFβ) by targeting SMAD7 for degradation. This mechanism is crucial for immune regulation and tumor rejection.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Signaling

Background:

  • T cell-intrinsic transforming growth factor beta (TGFβ) receptor signaling is vital for immune response regulation.
  • The E3 ligase Cbl-b influences T cell sensitivity to TGFβ, but the underlying mechanism remains unclear.

Purpose of the Study:

  • To elucidate the mechanism by which Cbl-b regulates TGFβ receptor (TGFβR) signaling in T cells.
  • To identify downstream targets of Cbl-b involved in TGFβ sensitivity.

Main Methods:

  • Investigated SMAD7 protein and mRNA levels in Cbl-b deficient (cblb(-/-)) T cells.
  • Assessed direct interaction and ubiquitination of SMAD7 by Cbl-b.
  • Utilized genetic knockout models (cblb(-/-) and SMAD7 loss) in mice to evaluate T cell responses and tumor rejection.

Main Results:

  • SMAD7 protein levels, not mRNA, were elevated in cblb(-/-) T cells, indicating posttranscriptional regulation.
  • Cbl-b directly ubiquitinates SMAD7, promoting its degradation.
  • Loss of SMAD7 in cblb(-/-) mice restored TGFβ sensitivity and abolished tumor rejection.

Conclusions:

  • Cbl-b directly targets SMAD7 for degradation, revealing a novel mechanism for controlling TGFβR signaling in T cells.
  • This Cbl-b-SMAD7 pathway plays a critical, non-redundant role in T cell immune responses and tumor immunity.
Keywords:
Cbl-bSMADTGFβ signaling

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