Mitochondrial chaperone Trap1 and the calcium binding protein Sorcin interact and protect cells against apoptosis...

Area of Science:

• Mitochondrial biology
• Cancer cell biology
• Molecular interactions

Background:

• Heat shock protein 75 (TRAP1), a mitochondrial chaperone, has antioxidant and antiapoptotic roles and is implicated in multidrug resistance in human colorectal carcinoma.
• Proteomic analysis identified Sorcin, a calcium-binding protein, as a novel interactor of TRAP1.

Purpose of the Study:

• To investigate the presence and function of Sorcin in human colon carcinoma cell mitochondria.
• To elucidate the interaction and regulatory relationship between Sorcin and TRAP1.

Main Methods:

• Proteomic analysis (coimmunoprecipitation) to identify TRAP1 interactors.
• Fluorescence microscopy and Western blot analysis of purified mitochondria and submitochondrial fractions.
• Gene silencing techniques (short hairpin RNA for TRAP1, small interfering RNA for Sorcin) to assess protein regulation.

Main Results:

• A specific Sorcin isoform (<20 kDa) was localized to mitochondria and shown to interact with TRAP1.
• TRAP1 and Sorcin exhibit reciprocal regulation: TRAP1 depletion reduces mitochondrial Sorcin, while Sorcin depletion increases TRAP1 degradation.
• The interaction between TRAP1 and Sorcin is essential for Sorcin's mitochondrial localization and TRAP1's stability.
• Intramitochondrial Sorcin appears to contribute to TRAP1-mediated cytoprotection.

Conclusions:

• Sorcin is a novel mitochondrial interactor of TRAP1, playing a key role in regulating TRAP1 stability and function.
• The TRAP1-Sorcin interaction is vital for mitochondrial localization and stability of both proteins.
• Sorcin's previously reported cytoprotective effects may be mediated through mitochondrial metabolism via the TRAP1 pathway.
• Both TRAP1 and Sorcin are implicated in multidrug resistance and are co-regulated in human colorectal carcinomas, suggesting potential therapeutic targets.