Discrete proteolysis of neuronal calcium sensor-1 (NCS-1) by mu-calpain disrupts calcium binding

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Neuronal calcium sensor-1 (NCS-1) is a Ca(2+)-binding protein modulating intracellular Ca(2+) signaling by interacting with the inositol 1,4,5-trisphosphate receptor (InsP3R).
• Paclitaxel (taxol), a chemotherapeutic agent, induces mu-calpain-dependent proteolysis of NCS-1, leading to reduced Ca(2+) signaling.
• NCS-1 degradation is implicated in paclitaxel-induced peripheral neuropathy, a common side effect in cancer patients.

Purpose of the Study:

• To identify the specific cleavage site of NCS-1 by mu-calpain.
• To investigate the functional consequences of NCS-1 cleavage on Ca(2+) binding and signaling.
• To explore therapeutic strategies for preventing paclitaxel-induced peripheral neuropathy by protecting NCS-1.

Main Methods:

• In vitro treatment of NCS-1 with mu-calpain.
• N-terminal sequencing and MALDI mass spectrometry to identify the cleavage site.
• Isothermal titration calorimetry (ITC) to assess Ca(2+) binding affinity of cleaved NCS-1.

Main Results:

• Mu-calpain cleaves NCS-1 within an N-terminal pseudoEF-hand domain.
• The pseudoEF-hand domain is crucial for stabilizing NCS-1's functional EF-hands and high Ca(2+) affinity.
• Cleavage significantly reduces NCS-1's affinity for Ca(2+), impairing its ability to respond to Ca(2+) level changes.

Conclusions:

• Paclitaxel-induced NCS-1 cleavage by mu-calpain disrupts Ca(2+) signaling by reducing Ca(2+) binding affinity.
• The N-terminal pseudoEF-hand plays a critical role in maintaining NCS-1's Ca(2+) sensing capabilities.
• Targeting the NCS-1 cleavage site or enhancing its Ca(2+) binding could be a therapeutic strategy against taxol-induced peripheral neuropathy.