Cancer-associated mutations in protein kinase C theta are loss-of-function

Area of Science:

• Molecular Biology
• Cancer Biology
• Biochemistry

Background:

• Protein kinase C theta (PKCθ) is crucial in immune signaling and platelet function, highly expressed in hematopoietic cells.
• Emerging evidence links PKCθ to various cancers, but its precise role and therapeutic targeting remain unclear.
• Understanding how cancer-associated mutations affect PKCθ activity and stability is vital for its oncogenic or tumor-suppressive potential.

Purpose of the Study:

• To investigate the impact of four cancer-associated mutations on PKCθ cellular activity and stability.
• To elucidate the mechanisms by which these mutations lead to loss-of-function.
• To assess the overall role of PKCθ in cancer development.

Main Methods:

• Utilized live-cell imaging with a Förster resonance energy transfer (FRET)-based reporter (CKAR2) to monitor PKC activity.
• Analyzed mutations in the autoinhibitory pseudosubstrate, C1A domain, and C-terminal tail of PKCθ.
• Performed bioinformatics analysis to correlate PKCθ protein levels with cancer patient data.

Main Results:

• Mutations in the pseudosubstrate and C1A domain impaired autoinhibition, increasing basal signaling and leading to protein degradation (loss-of-function).
• A C-terminal tail mutation enhanced autoinhibition and protein stability, also resulting in loss-of-function.
• Bioinformatics data showed reduced PKCθ protein levels across multiple cancer types (lung, renal, head and neck, pancreatic).

Conclusions:

• Cancer-associated mutations in PKCθ lead to its functional loss through distinct mechanisms: degradation or stabilization of an inactive state.
• PKCθ protein levels are diminished in diverse cancers, supporting its role as a tumor suppressor.
• The findings indicate a general loss of PKCθ function in cancer, highlighting its potential as a therapeutic target.