Role of the C-terminal domain of pulmonary surfactant protein A in binding to alveolar type II cells and regulation of phospholipid secretion

Surfactant protein A (SP-A), with a reduced denatured molecular mass of 26-38 kDa, is characterized by a collagen-like sequence in the N-terminal half of the protein. This protein forms an oligomeric structure which is dependent upon this collagenous domain. SP-A has been demonstrated to function as an inhibitor of phospholipid secretion by primary cultures of alveolar type II cells via a cell surface receptor for the protein. However, the receptor-binding domain of SP-A has not been identified. The purpose of the present study was to investigate the role of the C-terminal domain of SP-A in binding to type II cells and regulation of phospholipid secretion. A monoclonal antibody to human SP-A, whose epitope was localized at the C-terminal domain of the protein, abolished the inhibitory activity of human SP-A on lipid secretion by type II cells, and attenuated the ability of human SP-A to compete with 125I-(rat SP-A) for receptor binding. SP-A was then digested with collagenase and the collagenase-resistant fragment (CRF), which is the C-terminal domain of SP-A (thus lacking the N-terminal domain), was isolated. Gel filtration chromatography revealed that CRF exists as a monomer in solution containing Ca2+. CRF had the ability to inhibit phospholipid secretion, although at a higher concentration than for SP-A, and was also able to compete with 125I-(rat SP-A) for binding to type II cells. A direct binding study showed that CRF bound to type II cells in a concentration-dependent manner. The present study demonstrates that the non-collagenous, C-terminal, domain of SP-A is responsible for the protein's inhibitory effect on lipid secretion and its binding to type II cells.

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Design-based stereological analysis of the lung parenchymal architecture and alveolar type II cells in surfactant protein A and D double deficient mice

The Anatomical Record Part A Discoveries in Molecular Cellular and Evolutionary Biology ◽

10.1002/ar.a.20225 ◽

2005 ◽

Vol 286A (2) ◽

pp. 885-890 ◽

Cited By ~ 25

Author(s):

Anja Jung ◽

Lennell Allen ◽

Jens R. Nyengaard ◽

Hans Jørgen G. Gundersen ◽

Joachim Richter ◽

...

Keyword(s):

Protein A ◽

Surfactant Protein ◽

Surfactant Protein A ◽

Alveolar Type ◽

Type Ii Cells ◽

Type Ii ◽

Alveolar Type Ii Cells ◽

Stereological Analysis ◽

Deficient Mice

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Alveolar Type II Cells, Surfactant Protein A (SP-A), and the Phospholipid Components of Surfactant in Acute Silicosis in the Rat

American Review of Respiratory Disease ◽

10.1164/ajrccm/140.2.460 ◽

1989 ◽

Vol 140 (2) ◽

pp. 460-470 ◽

Cited By ~ 56

Author(s):

Hiroshi Kawada ◽

Tadashi Horiuchi ◽

John M. Shannon ◽

Yoshio Kuroki ◽

Dennis R. Voelker ◽

...

Keyword(s):

Protein A ◽

Surfactant Protein ◽

Surfactant Protein A ◽

Alveolar Type ◽

Type Ii Cells ◽

Type Ii ◽

Alveolar Type Ii Cells

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Internalization of surfactant protein A (SP-A) into lamellar bodies of rat alveolar type II cells in vitro.

Journal of Histochemistry & Cytochemistry ◽

10.1177/41.1.8417113 ◽

1993 ◽

Vol 41 (1) ◽

pp. 57-70 ◽

Cited By ~ 18

Author(s):

M Kalina ◽

F X McCormack ◽

H Crowley ◽

D R Voelker ◽

R J Mason

Keyword(s):

Protein A ◽

Fluid Phase ◽

Surfactant Protein ◽

Biologically Active ◽

Surfactant Protein A ◽

Alveolar Type ◽

Type Ii Cells ◽

Type Ii ◽

Lamellar Bodies ◽

Alveolar Type Ii Cells

Pulmonary surfactant is thought to be internalized and processed for reuse by alveolar Type II cells. In the present study we followed the internalization and intracellular trafficking of purified surfactant protein A (SP-A) by primary cultures of alveolar Type II cells. Internalization of native rat SP-A was compared with that of recombinant rat and human SP-A isolated from a patient with alveolar proteinosis. All SP-A species were conjugated with colloidal gold for visualization by electron microscopy. The gold conjugates were biologically active, as demonstrated by inhibition of phospholipid secretion from alveolar Type II cells. The SP-A-gold conjugates were internalized to lamellar bodies (LB) via the endosomal system, which included both electron-lucent and -dense multivesicular bodies. Labeling of LB was time dependent, and after 7 hr 30-40% of these organelles were labeled. Alkylation of SP-A greatly reduced internalization, as did an excess of non-conjugated SP-A. No qualitative differences in uptake were observed with the three forms of SP-A. The percent of labeled LB was similar (30-40%) after 7 hr of internalization with the three species of SP-A. The recombinant SP-A produced using a baculovirus vector lacked hydroxyproline and had an altered oligosaccharide, but these features did not affect its internalization or the rate of LB labeling. Internalization of the gold-conjugated SP-A and endocytosis of the fluid-phase marker Lucifer Yellow were related to the shape of Type II cells. Both uptake of SP-A, which is receptor mediated, and fluid-phase endocytosis were found to be less active in the flattened than in the rounded cells. Therefore, cell shape and hence cytoskeletal organization may play an important role in SP-A recycling. However, it is possible that both morphology and decreased endocytosis are independent manifestations related to the loss of differentiated function of cultured Type II cells.

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