Ca²⁺/calmodulin-dependent protein kinase II β decodes ER Ca²⁺ transients to trigger autophagosome formation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Autophagy is a fundamental cellular process for maintaining homeostasis.
• The precise mechanisms by which calcium (Ca2+) signals on the ER surface trigger autophagosome formation remain largely unknown.
• Understanding these signaling pathways is critical for cellular health and disease.

Purpose of the Study:

• To elucidate the role of Ca2+ transients in initiating autophagy.
• To identify key molecular players involved in decoding Ca2+ signals for autophagosome formation.
• To investigate the function of CaMKIIβ in integrating Ca2+ signaling with autophagy initiation.

Main Methods:

• Investigated Ca2+ signaling dynamics during autophagy induction using live-cell imaging.
• Utilized biochemical assays to analyze protein-protein interactions and phosphorylation events.
• Employed genetic manipulation (mutagenesis) to assess the functional impact of CaMKIIβ in autophagy.
• Studied liquid-liquid phase separation (LLPS) of the FIP200 complex in vitro and in cells.

Main Results:

• Ca2+/calmodulin-dependent protein kinase II β (CaMKIIβ) integrates ER Ca2+ transients to trigger LLPS of the FIP200 complex.
• CaMKIIβ is recruited to the ER and phosphorylates FIP200, modulating LLPS and autophagosome formation.
• CaMKIIβ controls the amplitude, duration, and propagation of ER Ca2+ transients during autophagy.
• Mutations in CaMKIIβ associated with MRD54 impair its autophagic function.

Conclusions:

• CaMKIIβ is essential for sustaining and decoding ER Ca2+ transients to specify autophagosome formation.
• CaMKIIβ acts as a critical molecular integrator of Ca2+ signals and autophagy initiation.
• Dysregulation of CaMKIIβ-mediated signaling contributes to neurodevelopmental disorders like MRD54.