Alveolar type II cells express a high-affinity receptor for pulmonary surfactant protein A.
Primary cultures of rat alveolar type II cells bind radiolabeled pulmonary surfactant protein A (SP-A) with high affinity. The binding of 125I-labeled SP-A is time- and temperature-dependent and is not accompanied by significant degradation. The binding process is saturable at low concentrations of SP-A (5 micrograms/ml), and unlabeled SP-A readily competes with labeled SP-A for cellular binding sites. Subsequent to binding, two pools of cell-associated 125I-labeled SP-A can be identified based upon sensitivity to trypsin at 0 degrees C. It is likely that the trypsin-sensitive pool comprises 125I-labeled SP-A bound to the cell surface and the trypsin-insensitive pool comprises the internalized protein. Scatchard analysis of cell surface binding of SP-A at 0.1-10 micrograms/ml shows positive cooperativity at concentrations between 0.1 and 1 micrograms/ml. Hill plots give nH = 1.34 +/- 0.08 with an apparent dissociation constant K'd = 1.02 +/- 0.32 micrograms/ml (which is 0.64 +/- 0.19 nM if the native molecular mass of oligomeric SP-A is assumed to be 1.6 MDa). The binding of SP-A to type II cells shows an absolute requirement for Ca2+. The putative receptor for SP-A is unaffected by treatment of type II cells with a variety of proteases and N-Glycanase (EC 3.5.1.52). Alveolar macrophages also exhibit high-affinity binding of SP-A, but rat lung fibroblasts and the alveolar epithelial cell line L2 exhibit only nonspecific binding.
Kuroki
Y
Y
National Jewish Center for Immunology and Respiratory Medicine, Denver, CO 80206.
Mason
R J
RJ
Voelker
D R
DR
D000818:Animals; D001059:Apoproteins / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D005347:Fibroblasts; D008297:Male; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000032:analysis / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
D001059:Apoproteins; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D011956:Receptors, Cell Surface; C046616:pulmonary surfactant apoprotein