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E3 Ubiquitin Ligase Mind Bomb 1 is a Novel Negative Regulator of Tumor-Suppressive BMP Signaling

Charisa L Cottonham1, Gloria E Hernandez1,2, Tommy K Cheung3

  • 1Department of Discovery Oncology, Genentech, South San Francisco, California.

Cancer Research Communications
|July 29, 2026
PubMed

Insights

Mindbomb1 (MIB1) regulates Bone Morphogenic Protein (BMP) signaling, acting as a tumor suppressor. MIB1 loss enhances BMP signaling and tumor suppression, revealing a new role for MIB1 in cancer biology.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cell Signaling

Background:

  • Mindbomb1 (MIB1) is an E3 ubiquitin ligase crucial for NOTCH activation.
  • Genome-wide screens identified MIB1 as a cancer dependency, unexpectedly linking it to Transforming Growth Factor-β (TGF-β) and Bone Morphogenic Protein (BMP) signaling, not NOTCH.
  • The precise role of MIB1 in TGF-β/BMP pathways remained unclear.

Purpose of the Study:

  • To investigate the unexpected link between MIB1 and BMP signaling identified in cancer cell line screens.
  • To elucidate the functional role of MIB1 in regulating BMP signaling pathways in cancer.
  • To determine the implications of MIB1's function in BMP signaling for cancer biology.

Main Methods:

  • Genetic manipulation (MIB1 depletion and re-expression) and pharmacologic inhibition of BMP signaling.
  • Assessment of BMP signaling activation through SMAD1/5/9 phosphorylation and transcriptional responses.
  • Co-immunoprecipitation to confirm physical interaction between MIB1 and BMP receptors.

Main Results:

  • MIB1 loss phenocopied BMP's tumor suppressive functions, leading to growth inhibition in MIB1-dependent cancer cells.
  • MIB1 depletion selectively enhanced BMP signaling, evidenced by increased SMAD1/5/9 phosphorylation and transcriptional activity, correlated with higher BMP receptor levels.
  • Re-expression of a catalytically inactive MIB1 mutant failed to rescue growth inhibition, indicating E3 ligase activity is essential for MIB1's negative regulatory function.
  • MIB1 physically associates with the BMP type II receptor (BMPR2) in cancer and endothelial cells.

Conclusions:

  • MIB1 functions as a novel, Notch-independent negative regulator of BMP signaling.
  • MIB1's E3 ligase activity is critical for its role in suppressing BMP signaling.
  • This discovery expands the known functions of MIB1 in cancer biology and suggests therapeutic potential in targeting BMP signaling.

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