Alpha-actinin-4 and CLP36 protein deficiencies contribute to podocyte defects in multiple human glomerulopathies

J Biol Chem. 2011 Sep 2;286(35):30795-30805. doi: 10.1074/jbc.M111.255984. Epub 2011 Jun 16.

Abstract

Genetic alterations of α-actinin-4 can cause podocyte injury through multiple mechanisms. Although a mechanism involving gain-of-α-actinin-4 function was well described and is responsible for a dominantly inherited form of human focal segmental glomerulosclerosis (FSGS), evidence supporting mechanisms involving loss-of-α-actinin-4 function in human glomerular diseases remains elusive. Here we show that α-actinin-4 deficiency occurs in multiple human primary glomerulopathies including sporadic FSGS, minimal change disease, and IgA nephropathy. Furthermore, we identify a close correlation between the levels of α-actinin-4 and CLP36, which form a complex in normal podocytes, in human glomerular diseases. siRNA-mediated depletion of α-actinin-4 in human podocytes resulted in a marked reduction of the CLP36 level. Additionally, two FSGS-associated α-actinin-4 mutations (R310Q and Q348R) inhibited the complex formation between α-actinin-4 and CLP36. Inhibition of the α-actinin-4-CLP36 complex, like loss of α-actinin-4, markedly reduced the level of CLP36 in podocytes. Finally, reduction of the CLP36 level or disruption of the α-actinin-4-CLP36 complex significantly inhibited RhoA activity and generation of traction force in podocytes. Our studies reveal a critical role of the α-actinin-4-CLP36 complex in podocytes and provide an explanation as to how α-actinin-4 deficiency or mutations found in human patients could contribute to podocyte defects and glomerular failure through a loss-of-function mechanism.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actinin / deficiency
  • Actinin / genetics*
  • Animals
  • Biopsy
  • Detergents / pharmacology
  • Glomerulonephritis, IGA / metabolism
  • Glomerulosclerosis, Focal Segmental / metabolism
  • Humans
  • Immunohistochemistry / methods
  • Kidney / metabolism
  • Kidney Glomerulus / metabolism*
  • LIM Domain Proteins
  • Mice
  • Microfilament Proteins / deficiency
  • Microfilament Proteins / genetics*
  • Mutation
  • Podocytes / metabolism*
  • Protein Interaction Mapping / methods
  • Proteinuria / metabolism
  • Transcription Factors

Substances

  • ACTN4 protein, human
  • Detergents
  • LDB2 protein, human
  • LIM Domain Proteins
  • Microfilament Proteins
  • Transcription Factors
  • Actinin