Sodium 4-phenylbutyrate downregulates HSC70 expression by facilitating mRNA degradation

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Cystic fibrosis transmembrane conductance regulator (CFTR) protein misfolding and degradation is a key issue in cystic fibrosis.
• Sodium 4-phenylbutyrate (4PBA) is known to correct DeltaF508 CFTR trafficking, but the underlying mechanism is unclear.
• Heat shock cognate protein 70 (HSC70) is implicated in the degradation of misfolded proteins, including DeltaF508 CFTR.

Purpose of the Study:

• To investigate the mechanism by which 4PBA reduces HSC70 expression.
• To determine if 4PBA affects HSC70 gene transcription or mRNA stability.
• To elucidate the impact of 4PBA on HSC70 protein synthesis and degradation.

Main Methods:

• Luciferase reporter assays were used to assess HSC70 promoter activity.
• Nuclear runoff assays measured HSC70 mRNA synthesis rates.
• Analysis of HSC70 mRNA degradation rates.
• Measurement of 35S-labeled HSC70 protein synthesis and degradation rates.

Main Results:

• 4PBA treatment (1 mM) did not alter HSC70 promoter activity or mRNA synthesis.
• 4PBA significantly increased the degradation rate of HSC70 mRNA by approximately 40%.
• 4PBA reduced the initial rate of HSC70 protein synthesis and steady-state accumulation by about 40% without affecting protein degradation.

Conclusions:

• 4PBA decreases HSC70 mRNA and protein expression primarily by increasing HSC70 mRNA instability.
• These findings suggest that 4PBA-induced destabilization of HSC70 mRNA is a key mechanism for its therapeutic effect on DeltaF508 CFTR trafficking.
• Targeting mRNA stability offers a potential therapeutic strategy for cystic fibrosis and other protein-misfolding diseases.