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Small heat-shock proteins select deltaF508-CFTR for endoplasmic reticulum-associated degradation

Annette Ahner1, Kunio Nakatsukasa, Hui Zhang

  • 1Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.

Molecular Biology of the Cell
|December 22, 2006
PubMed

Insights

Small heat-shock proteins (sHsps) stabilize misfolded cystic fibrosis transmembrane conductance regulator (CFTR) by preventing its degradation. This suggests sHsps play a role in managing CFTR protein quality control.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Protein Folding and Degradation

Background:

  • Misfolded proteins, like the DeltaF508 variant of cystic fibrosis transmembrane conductance regulator (CFTR), are targeted for endoplasmic reticulum (ER)-associated degradation (ERAD).
  • Molecular chaperones, including small heat-shock proteins (sHsps), are involved in protein quality control pathways.
  • HSP26, a yeast sHsp, is upregulated in response to CFTR expression, prompting investigation into the role of sHsps in CFTR ERAD.

Purpose of the Study:

  • To investigate the impact of small heat-shock proteins (sHsps) on the ER-associated degradation (ERAD) of cystic fibrosis transmembrane conductance regulator (CFTR).
  • To determine if sHsps are essential for CFTR polyubiquitination and degradation.
  • To explore the potential role of mammalian sHsps in CFTR biogenesis and degradation.

Main Methods:

  • Deletion of genes encoding yeast sHsps (Hsp26p and Hsp42p) to assess their effect on CFTR stability.
  • Analysis of ERAD for soluble and integral membrane proteins in yeast lacking specific sHsps.
  • Assessment of CFTR polyubiquitination in yeast deleted for sHsp genes.
  • Overexpression of a mammalian sHsp (alphaA-crystallin) in human cells to study its effect on wild-type and DeltaF508-CFTR.
  • Co-immunoprecipitation to examine interactions between alphaA-crystallin and DeltaF508-CFTR.
  • In vitro assays using purified alphaA-crystallin to assess its effect on CFTR protein aggregation.

Main Results:

  • CFTR was completely stabilized in yeast cells lacking the partially redundant sHsps, Hsp26p and Hsp42p.
  • ERAD of other proteins and CFTR polyubiquitination were unaffected in yeast lacking these sHsps, indicating they are not essential for these processes.
  • Overexpression of mammalian alphaA-crystallin enhanced DeltaF508-CFTR degradation but did not alter wild-type CFTR biogenesis.
  • AlphaA-crystallin preferentially interacted with DeltaF508-CFTR and suppressed the aggregation of a CFTR domain.

Conclusions:

  • Yeast Hsp26p and Hsp42p play a role in the degradation of CFTR, but are not essential for its polyubiquitination.
  • Mammalian alphaA-crystallin specifically targets the misfolded DeltaF508-CFTR variant, enhancing its degradation.
  • sHsps likely maintain the solubility of misfolded CFTR variants, such as DeltaF508-CFTR, during the ERAD process.

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