Research Focus >Protein Degradation

the projects -

protein degradation mechanisms

The regulated degradation of proteins is an important mechanism for the survival of cells. Accumulation of undegraded proteins in aggrosomes/inclusion bodies, or the premature degradation of (mutant) proteins is often associated with development of diseases, like cardiac and skeletal muscle myopathies.

protein degradation mechanisms - ubiquitin proteasome system UPS
Figure on the ubiquitin-proteasome system from the recently published book chapter in "Cardiac Cytoarchitecture: How to Maintain a Working Heart-Waste Disposal and Recycling in Cardiomyocytes".
Cardiac and skeletal muscle cells contain two major proteolytic systems for the degradation of proteins: the ubiquitin-proteasome system (UPS) and the autophagy/lysosome system. Degradation of most cellular proteins is achieved by way of the UPS and requires tagging of substrate proteins by ubiquitin (poly-ubiquitylation) through an enzymatic cascade.

protein degradation mechanisms - autophagy lysosome system
Figure on the autophagy-lysosome system from the recently published book chapter in "Cardiac Cytoarchitecture: How to Maintain a Working Heart-Waste Disposal and Recycling in Cardiomyocytes".

protein degradation in muscle

Considerable attention has been focused on muscle-specific UPS components. However, there is limited information on ubiquitously expressed E3-ligases for muscle protein turnover, and whether they may play a role for the development and progression of myopathies.

A role for cullin E3-ubiquitin ligases in muscle homeostasis is best characterized during muscle atrophy. In a research article, we investigated whether cullin activity was also crucial during terminal myoblast differentiation and aggregation of acetylcholine receptors for the establishment of neuromuscular junctions. We found that blockage of cullin activity using the small molecule inhibitor MLN4924 (Pevonedistat) completely abrogates terminal muscle formation.

cullin functions during muscle formation
This figure outlines cullin E3-ligase requirement in the terminal skeletal muscle differentiation process. The original article can be found at the Journal of Molecular Biology.

We recently summarized the surprisingly diverse roles that cullin-RING E3-ligases play for the development and function for cross-striated muscles as well as in disease. A special focus in this review article is put on the diversity in clinical myopathy phenotypes stemming from this E3-ligase family and its associated proteins, the use of inhibitors and model systems, as well as clinical perspectives.

cullin review
This composite figure outlines some of the highlights in the review article. We show the general layout of cullin-RING ligases, their regulation and modular make-up, highlight spatiotemporal expression patterns of cullin substrate adapter proteins, and showcase the surprising and enigmatic role that Obsl1 plays for cullin stability and localization. The original article can be found at the International Journal of Molecular Sciences.

the role of cullin-3 for skeletal muscles

In our new manuscript, we outlined the role that Cullin3 E3-ligase function plays for the development of nemaline myopathy in a murine model of the disease. Using mice that are deficient of Cullin-3, we define a novel molecular pathomechanism that may be at play in patients suffering from mutations in KBTBD13. The manuscript can be found at JCI Insight.

role of Cullin3 for NM

The original article can be found at JCI Insight.

Main objectives are to study:
  • further characterize muscle specific functions for E3-ligases of the cullin family
  • identify substrate-adaptor proteins for cullin-3
  • investigate the role for cullin-3 for myopathy development

Related Publications

  • The kinase domain of titin controls muscle gene expression and protein turnover. Lange S, Xiang F, Yakovenko A, Vihola A, Hackman P, Rostkova E, Kristensen J, Brandmeier B, Franzen G, Hedberg B, Gunnarsson LG, Hughes SM, Marchand S, Sejersen T, Richard I, Edstroem L, Ehler E, Udd B, Gautel M. Science. 2005 Jun 10;308(5728):1599-603. PMID: 15802564

  • Obscurin and KCTD6 regulate cullin-dependent small ankyrin-1 (sAnk1.5) protein turnover. Lange S, Perera S, Teh P, Chen J. Mol Biol Cell. 2012 Jul;23(13):2490-504. PMID: 22573887

  • Breaking down protein degradation mechanisms in cardiac muscle. Lyon RC, Lange S, Sheikh F. Trends Mol Med. 2013 Apr;19(4):239-49. PMID: 23453282

  • Cardiac Cytoarchitecture: How to Maintain a Working Heart-Waste Disposal and Recycling in Cardiomyocytes. Jordan Blondelle & Stephan Lange. Book Chapter in Cardiac Cytoarchitecture. Edited by Elisabeth Ehler. Springer International Publishing Switzerland. 2015. ISBN: 978-3-319-15262-2 (Print) 978-3-319-15263-9 (Online). Online Version

  • Cullin E3 ligase activity is required for myoblast differentiation. Jordan Blondelle, Paige Shapiro, Andrea A. Domenighetti, Stephan Lange. JMB. 2017.

  • Cullin-3 dependent deregulation of ACTN1 represents a new pathogenic mechanism in nemaline myopathy. Blondelle J, Tallapaka K, Seto JT, Ghassemian M, Clark M, Laitila JM, Bournazos A, Singer JD, Lange S. JCI Insight. 2019 Apr 16.

  • The Role of Cullin-RING Ligases in Striated Muscle Development, Function, and Disease. Blondelle J, Biju A, Lange S. IJMS. 2020, 21(21), 7936.

Future Directions

We are currently investigating whether E3-ligases of the cullin protein family play a greater role for muscle specific protein turnover than previously anticipated. Of particular interest is the possible role that cullin-3 plays for the development of skeletal and cardiac muscles as well as motor neurons. We also study pathophysiological roles of cullin-3 for the etiology of neuromuscular diseases and cardomyopathies.

Collaborators on this project

  • Dr. Jeffrey Singer at Portland State University, OR
  • Dr. Jane Seto at Murdoch Children's Hospital, Australia
  • Drs. Careina Wallgren-Pettersson & Katarina Pelin at the University of Helsinki, Finland
Keywords: degradation, cullin, E3-ligase, ubiquitin.