HSC70 is a chaperone for wild-type and mutant cardiac myosin binding protein C

Area of Science:

• Molecular biology
• Cardiovascular research
• Protein biochemistry

Background:

• Cardiac myosin binding protein C (MYBPC3) mutations are the leading cause of hypertrophic cardiomyopathy (HCM).
• Both MYBPC3 haploinsufficiency and proteostasis disruption are implicated in HCM pathogenesis.
• Understanding MYBPC3 protein turnover is essential to differentiate these pathogenic mechanisms.

Purpose of the Study:

• To investigate the regulation of wild-type (WT) and mutant MYBPC3 protein turnover.
• To identify proteins involved in MYBPC3 degradation pathways.
• To elucidate the role of chaperone systems in MYBPC3 homeostasis.

Main Methods:

• Expression of MYBPC3 mutations in neonatal rat ventricular cardiomyocytes.
• Coimmunoprecipitation followed by mass spectrometry to identify protein interactors.
• HSC70 knockdown and pharmacologic activation to study protein degradation rates.
• Immunofluorescence microscopy to assess protein localization.

Main Results:

• Mutant MYBPC3 proteins exhibited reduced expression and failed sarcomeric localization compared to WT MYBPC3.
• HSP70-family chaperones, particularly heat shock cognate 70 kDa (HSC70), were identified as MYBPC3 interactors.
• HSC70 knockdown slowed MYBPC3 degradation, while HSC70/HSP70 activation accelerated it.
• Mutant MYBPC3 did not disrupt HSC70 localization or induce general proteostasis dysfunction.

Conclusions:

• WT and mutant MYBPC3 proteins serve as clients for the HSC70 chaperone system.
• The HSC70 chaperone system plays a significant role in regulating MYBPC3 protein turnover.
• This regulation is a key factor in the context of hypertrophic cardiomyopathy.