ASB2 is a novel E3 ligase of SMAD9 required for cardiogenesis

Sci Rep. 2021 Nov 29;11(1):23056. doi: 10.1038/s41598-021-02390-0.


Cardiogenesis requires the orchestrated spatiotemporal tuning of BMP signalling upon the balance between induction and counter-acting suppression of the differentiation of the cardiac tissue. SMADs are key intracellular transducers and the selective degradation of SMADs by the ubiquitin-proteasome system is pivotal in the spatiotemporal tuning of BMP signalling. However, among three SMADs for BMP signalling, SMAD1/5/9, only the specific E3 ligase of SMAD9 remains poorly investigated. Here, we report for the first time that SMAD9, but not the other SMADs, is ubiquitylated by the E3 ligase ASB2 and targeted for proteasomal degradation. ASB2, as well as Smad9, is conserved among vertebrates. ASB2 expression was specific to the cardiac region from the very early stage of cardiac differentiation in embryogenesis of mouse. Knockdown of Asb2 in zebrafish resulted in a thinned ventricular wall and dilated ventricle, which were rescued by simultaneous knockdown of Smad9. Abundant Smad9 protein leads to dysregulated cardiac differentiation through a mechanism involving Tbx2, and the BMP signal conducted by Smad9 was downregulated under quantitative suppression of Smad9 by Asb2. Our findings demonstrate that ASB2 is the E3 ligase of SMAD9 and plays a pivotal role in cardiogenesis through regulating BMP signalling.

MeSH terms

  • Animals
  • Bone Morphogenetic Proteins / metabolism
  • Cell Differentiation
  • Gene Expression Profiling
  • Gene Expression Regulation, Developmental
  • HEK293 Cells
  • Heart* / embryology
  • Humans
  • Mice
  • Oligonucleotide Array Sequence Analysis
  • Proteasome Endopeptidase Complex / metabolism
  • Signal Transduction
  • Smad8 Protein* / biosynthesis
  • Smad8 Protein* / physiology
  • Suppressor of Cytokine Signaling Proteins* / biosynthesis
  • Suppressor of Cytokine Signaling Proteins* / physiology
  • Ubiquitin / chemistry
  • Ubiquitin / physiology
  • Ubiquitin-Protein Ligases / metabolism
  • Zebrafish


  • Asb2 protein, mouse
  • ASB2 ubiqutin ligase, zebrafish
  • Bone Morphogenetic Proteins
  • Proteasome Endopeptidase Complex
  • Smad8 Protein
  • Smad9 protein, mouse
  • Suppressor of Cytokine Signaling Proteins
  • Ubiquitin
  • Ubiquitin-Protein Ligases
  • SMAD9 protein, zebrafish