The mammalian Sec6/8 complex interacts with Ca(2+) signaling complexes and regulates their activity

Area of Science:

• Cell Biology
• Molecular Biology
• Physiology

Background:

• Polarized localization of calcium (Ca2+) transport and signaling proteins is crucial for agonist-stimulated Ca2+ waves in secretory cells.
• The Sec6/8 complex, also known as the exocyst, is implicated in protein trafficking and vesicle exocytosis.

Purpose of the Study:

• To investigate the role of the Sec6/8 complex in polarized Ca2+ signaling within pancreatic acinar cells.
• To determine the cellular localization and interaction partners of the Sec6/8 complex in relation to Ca2+ signaling machinery.

Main Methods:

• Immunolocalization using confocal microscopy to determine Sec6/8 complex localization.
• Immunoprecipitation (IP) assays to identify protein interaction partners of Sec6/8.
• Functional assays involving antibody inhibition and actin cytoskeleton disruption (latrunculin B) to assess the impact on Ca2+ signaling.

Main Results:

• The Sec6/8 complex localizes to the Golgi apparatus and near the plasma membrane at the apical pole, distinct from tight junctions and secretory granules.
• Sec6/8 co-immunoprecipitates with inositol 1,4,5-trisphosphate receptors (IP3R3), G protein subunits (Galphaq, Gbetagamma), phospholipase C (PLC), and the plasma membrane Ca2+ pump.
• Actin cytoskeleton disruption releases Ca2+ signaling proteins from the Sec6/8 complex and inhibits agonist-evoked Ca2+ waves, indicating a crucial role for actin in mediating these interactions.

Conclusions:

• The Sec6/8 complex plays a significant role in regulating polarized Ca2+ signaling in secretory cells.
• The interaction between the Sec6/8 complex and Ca2+ signaling proteins is dependent on the actin cytoskeleton.
• The Sec6/8 complex governs the polarized distribution and activity of Ca2+ signaling complexes, impacting Ca2+ wave propagation.