The ubiquitin ligase Ubr4 controls stability of podocin/MEC-2 supercomplexes

Hum Mol Genet. 2016 Apr 1;25(7):1328-44. doi: 10.1093/hmg/ddw016. Epub 2016 Jan 19.

Abstract

The PHB-domain protein podocin maintains the renal filtration barrier and its mutation is an important cause of hereditary nephrotic syndrome. Podocin and its Caenorhabditis elegans orthologue MEC-2 have emerged as key components of mechanosensitive membrane protein signalling complexes. Whereas podocin resides at a specialized cell junction at the podocyte slit diaphragm, MEC-2 is found in neurons required for touch sensitivity. Here, we show that the ubiquitin ligase Ubr4 is a key component of the podocin interactome purified both from cultured podocytes and native glomeruli. It colocalizes with podocin and regulates its stability. In C. elegans, this process is conserved. Here, Ubr4 is responsible for the degradation of mislocalized MEC-2 multimers. Ubiquitylomic analysis of mouse glomeruli revealed that podocin is ubiquitylated at two lysine residues. These sites were Ubr4-dependent and were conserved across species. Molecular dynamics simulations revealed that ubiquitylation of one site, K301, do not only target podocin/MEC-2 for proteasomal degradation, but may also affect stability and disassembly of the multimeric complex. We suggest that Ubr4 is a key regulator of podocyte foot process proteostasis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Caenorhabditis elegans / metabolism
  • Caenorhabditis elegans Proteins / metabolism*
  • Calmodulin-Binding Proteins / metabolism*
  • Cytoskeletal Proteins / metabolism*
  • Humans
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Kidney Glomerulus / metabolism*
  • Male
  • Membrane Proteins / metabolism*
  • Mice
  • Microtubule-Associated Proteins / metabolism*
  • Molecular Dynamics Simulation
  • Nephrotic Syndrome / metabolism
  • Ubiquitin-Protein Ligases / metabolism*
  • Ubiquitination

Substances

  • Caenorhabditis elegans Proteins
  • Calmodulin-Binding Proteins
  • Cytoskeletal Proteins
  • Intracellular Signaling Peptides and Proteins
  • MEC-2 protein, C elegans
  • Membrane Proteins
  • Microtubule-Associated Proteins
  • NPHS2 protein
  • ubiquitin ligase Ubr4, C elegans
  • UBR4 protein, human
  • Ubiquitin-Protein Ligases
  • Ubr4 protein, mouse