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Functional Reconstitution and Channel Activity Measurements of Purified Wildtype and Mutant CFTR Protein
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Sodium 4-phenylbutyrate downregulates Hsc70: implications for intracellular trafficking of DeltaF508-CFTR

R C Rubenstein1, P L Zeitlin

  • 1Division of Pulmonary Medicine, Children's Hospital of Philadelphia and Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA. rrubenst@mail.med.upenn.edu

American Journal of Physiology. Cell Physiology
|February 9, 2000
PubMed

Insights

Sodium 4-phenylbutyrate (4PBA) reduces Hsc70 expression, improving the trafficking of the common cystic fibrosis transmembrane conductance regulator (CFTR) mutation DeltaF508 by decreasing its association with Hsc70.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • The DeltaF508 mutation is the most common cause of cystic fibrosis (CF), resulting in a misfolded CFTR protein.
  • Misfolded DeltaF508-CFTR protein is targeted for degradation via the ubiquitin-proteasome system, partly due to prolonged association with molecular chaperones.
  • Sodium 4-phenylbutyrate (4PBA) has shown potential in improving DeltaF508-CFTR trafficking and function.

Purpose of the Study:

  • To investigate the mechanism by which 4PBA enhances DeltaF508-CFTR trafficking.
  • To test the hypothesis that 4PBA reduces Hsc70 expression, thereby modulating DeltaF508-CFTR ubiquitination and degradation.

Main Methods:

  • Treatment of IB3-1 cystic fibrosis epithelial cells (DeltaF508/W1282X genotype) with varying concentrations of 4PBA.
  • Assessment of Hsc70 protein and mRNA levels using Western blot and quantitative PCR.
  • Immunoprecipitation assays to analyze the association between Hsc70 and CFTR.

Main Results:

  • 4PBA treatment resulted in a dose-dependent decrease in Hsc70 protein and mRNA levels in IB3-1 cells.
  • Immunoprecipitation studies showed that 4PBA treatment reduced the association between Hsc70 and CFTR.
  • Levels of other chaperones including Hsp40, Hdj2, Hsp70, Hsp90, and calnexin remained unaffected by 4PBA.

Conclusions:

  • 4PBA may enhance DeltaF508-CFTR trafficking by reducing its interaction with Hsc70.
  • This reduced association allows a larger proportion of mutant CFTR to escape degradation.
  • The findings provide insights into the therapeutic mechanism of 4PBA for cystic fibrosis.

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