AJP - Lung Cellular and Molecular Physiology, Vol 273, Issue 1 159-L171, Copyright © 1997 by American Physiological Society

ARTICLES

Distinct effects of SP-A and SP-B on endocytosis of SP-C by pulmonary epithelial cells

A. D. Horowitz, B. Moussavian, E. D. Han, J. E. Baatz and J. A. Whitsett
Division of Pulmonary Biology, Children's Hospital Research Foundation, Cincinnati, Ohio 45229, USA.

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.

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