Abstract
Lung surfactant is secreted through the fusion of lamellar bodies with the plasma membrane of alveolar epithelial type II cells. Annexin A2, a Ca 2+- and phospholipid-binding protein, promotes the fusion of lamellar bodies with the plasma membrane. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are known to have an essential role in surfactant secretion. We hypothesized that annexin A2 acts as a Ca2+ sensor and mediates membrane fusion via its interaction with SNAREs. Both purified or endogenous annexin A2 in type II cells specifically bound with SNAP-23 in a Ca2+-dependent manner, as determined by pull-down experiments using recombinant glutathione S-transferase-tagged SNAP-23. A deletion study identified the cysteine-rich region (CRR) of SNAP-23 as the binding site for annexin A2. Mutations of cysteine residues in the CRR dramatically decreased the binding. SNAP-23 also co-immunoprecipitated with annexin A2; however, a SNAP-23 mutant failed to co-immunoprecipitate with annexin A2. Immunofluorescence revealed a co-localization of SNAP-23 and annexin A2 in type II cells. Furthermore, anti-SNAP-23 antibody significantly inhibited annexin A2-mediated fusion between lamellar bodies and the plasma membrane. These data suggest that annexin A2 and SNAP-23 are involved in the same pathway in the regulation of lung surfactant secretion.
Original language | English (US) |
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Pages (from-to) | 467-476 |
Number of pages | 10 |
Journal | American journal of respiratory cell and molecular biology |
Volume | 37 |
Issue number | 4 |
DOIs | |
State | Published - Oct 2007 |
Externally published | Yes |
Keywords
- Alveolar type II epithelial cells
- Annexin A2
- Lung surfactant
- Membrane fusion
- SNAP-23
ASJC Scopus subject areas
- Molecular Biology
- Pulmonary and Respiratory Medicine
- Clinical Biochemistry
- Cell Biology