Faculty Opinions recommendation of Direct interaction of surfactant protein A with myometrial binding sites: signaling and modulation by bacterial lipopolysaccharide.

Cultured alveolar type II cells and alveolar macrophages were found to secrete colony-stimulating factors (CSF) into the medium. Surfactant protein A (SP-A; 0.1-5 micrograms/ml) and bacterial lipopolysaccharide (LPS; 10-20 micrograms/ml) were found to upregulate the secretion of CSF (seven-fold) from these cells. However, a reversal of the stimulatory effect was observed when the two agents were added simultaneously to the cells. SP-A-enhanced phagocytosis of bacteria by alveolar macrophages was also inhibited by simultaneous addition of SP-A and LPS. Thus some biological activities attributed to either SP-A or LPS are inhibited in the simultaneous presence of the two agents. We therefore investigated the possibility of interaction and binding between SP-A and LPS molecules. Our biochemical data that include immunoblots and enzyme-linked immunosorbent assay support the notion that SP-A is capable of binding LPS, and this interaction is time and concentration dependent. The binding was partially inhibited (60%) by antibody to SP-A. The binding was calcium independent and was not affected by excess carbohydrates such as methyl alpha-D-mannopyranoside or heparin. Lipid A, the hydrophobic component of LPS, however, inhibited the SP-A-LPS interaction and also caused a partial reversal of the binding. Thus these results indicate that lipid A is associated with this binding. The biological implication of SP-A-LPS interaction, especially during inflammatory responses, is discussed.

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Mechanism for secretagogue-induced surfactant protein A binding to lung epithelial cells

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1998.275.1.l38 ◽

1998 ◽

Vol 275 (1) ◽

pp. L38-L46 ◽

Cited By ~ 3

Author(s):

Qiping Chen ◽

Aron B. Fisher ◽

David S. Strayer ◽

Sandra R. Bates

Keyword(s):

Plasma Membrane ◽

Cell Surface ◽

Binding Sites ◽

Cell Membranes ◽

Protein A ◽

Surfactant Protein ◽

Surfactant Protein A ◽

Type Ii Cells ◽

Type Ii ◽

Type Ii Cell

Secretagogues stimulate both secretion and reuptake of surfactant components by pulmonary type II cells as well as enhance surfactant protein A (SP-A) binding. We have evaluated the possibility that the observed increase in SP-A binding is due to the movement of SP-A receptors from an intracellular pool to the plasma membrane. We utilized an anti-idiotypic monoclonal antibody, A2R, which recognizes an SP-A binding protein on type II cell membranes. Immunocytochemistry studies showed that A2R reacted with cellular antigens on type II cell membranes and paranuclear granules. A2R inhibited cell association of125I-SP-A to type II cells plated on Transwell membranes as well as those plated on plastic dishes and also inhibited the SP-A-stimulated incorporation of phosphatidylcholine liposomes into type II cells. On exposure to secretagogues, the binding of 125I-A2R and125I-SP-A to type II cells increased in parallel. With permeabilized type II cells on Transwell membranes, one-sixth of the binding sites were located on the plasma membrane, with the remainder being intracellular; phorbol 12-myristate 13-acetate treatment increased the binding of A2R to the cell surface but did not affect the total binding of A2R. Ligand blots of type II cell plasma membranes showed that SP-A and A2R both bound proteins with molecular masses of ∼32 and 60 kDa, respectively, reduced. Under nonreducing conditions, the mass of the SP-A and A2R binding protein was ∼210 kDa, indicating that the SP-A receptor is composed of disulfide-linked subunits. The results support our hypothesis that secretagogues increase SP-A binding sites by accelerating recruitment of receptors to the cell surface.

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