Regulation of basal autophagy by calmodulin availability

Area of Science:

• Cell Biology
• Molecular Biology
• Autophagy Research

Background:

• Macroautophagy (autophagy) is a fundamental cellular process for maintaining homeostasis by degrading cellular components.
• Calmodulin (CaM), a Ca²⁺ sensor, regulates diverse cellular functions but its availability can be a limiting factor.
• The role of CaM availability in regulating basal autophagy has not been previously established.

Purpose of the Study:

• To investigate the hypothesis that CaM availability is a critical regulator of basal autophagy.
• To elucidate the mechanism by which CaM influences autophagic flux and lysosomal function.

Main Methods:

• Utilized CaM antagonists (W-7, trifluoperazine, CGS9343b) and chloroquine to assess effects on autophagy.
• Measured autophagosome accumulation, autophagic flux, AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) activity.
• Employed competitive binding assays, Ca²⁺ manipulation, and CaM buffering with high-affinity CaM-binding proteins.

Main Results:

• CaM antagonists and chloroquine inhibited basal autophagic flux and caused autophagosome accumulation, mimicking each other's effects.
• These reagents increased AMPK activity but not mTOR activity, and chloroquine directly bound CaM in a Ca²⁺ -dependent manner.
• CaM inhibition, rather than Ca²⁺ changes, was responsible for autophagy inhibition; CaM buffering increased lysosomal pH and LC3-II accumulation.

Conclusions:

• CaM availability is a prerequisite for basal autophagy.
• CaM regulates autophagy through mechanisms involving lysosomal pH and AMPK activation.
• This study reveals a novel regulatory role for CaM in maintaining cellular homeostasis via autophagy.