Distinct effects of SP-A and SP-B on endocytosis of SP-C by pulmonary epithelial cells.
Binding and endocytosis of surfactant protein (SP) C were assessed in a mouse pulmonary adenocarcinoma cell line, MLE-12, and in isolated rat pulmonary type II epithelial cells. Binding and uptake of SP-C were detected using fluorescently labeled SP-C and dinitrophenyl-labeled SP-C (DNP-SP-C). Endocytosis of DNP-SP-C was visualized by immunocytochemistry and light microscopy. Endocytosis of DNP-SP-C occurred in MLE-12 cells, pulmonary type II epithelial cells, and NIH/3T3 cells, indicating that uptake of SP-C does not have an absolute requirement for a cell-specific receptor. After 30-60 min at 37 degrees C, DNP-SP-C was concentrated in large intracellular bodies in MLE-12 cells. Endocytosis of DNP-SP-C by MLE-12 cells or type II epithelial cells was decreased by SP-B or SP-B and SP-A together. SP-A alone did not inhibit DNP-SP-C uptake. Endocytosis of DNP-SP-C was inhibited by a 10-fold excess of lipid vesicles containing SP-C but not by a 10-fold excess of lipid alone. The inhibitory effect of SP-B on SP-C uptake may play a role in maintaining surface-active material at the air-liquid interface.
Horowitz
A D
AD
Division of Pulmonary Biology, Children's Hospital Research Foundation, Cincinnati, Ohio 45229, USA.
Moussavian
B
B
Han
E D
ED
Baatz
J E
JE
Whitsett
J A
JA
D015060:1,2-Dipalmitoylphosphatidylcholine; D016475:3T3 Cells; D000230:Adenocarcinoma / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004140:Dinitrophenols; D004705:Endocytosis; D004848:Epithelium / Q000378:metabolism; D008168:Lung / Q000378:metabolism*; D008175:Lung Neoplasms / Q000378:metabolism; D051379:Mice; D010715:Phosphatidylglycerols; D011510:Proteolipids / Q000493:pharmacokinetics* / Q000494:pharmacology*; D011663:Pulmonary Surfactants / Q000493:pharmacokinetics* / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D004140:Dinitrophenols; D010715:Phosphatidylglycerols; D011510:Proteolipids; D011663:Pulmonary Surfactants; D015060:1,2-Dipalmitoylphosphatidylcholine; C030345:1,2-dipalmitoylphosphatidylglycerol