Glucocorticoids regulate surfactant protein synthesis in a pulmonary adenocarcinoma cell line.
Synthesis of pulmonary surfactant proteins SP-A, SP-B, and SP-C was demonstrated in a cell line derived from a human adenocarcinoma of the lung. The cells contained numerous lamellar inclusion bodies and formed organized groups of cells containing well-developed junctional complexes and apical microvillous membranes. Synthesis of SP-A was detected in the cells by enzyme-linked immunoabsorbent assay and by immunoprecipitation of [35S]methionine-labeled protein. SP-A was identified as an Mr 31,000-36,000 polypeptide containing asparagine-linked carbohydrate. Northern blot analysis detected SP-A mRNA of 2.2 kb. Dexamethasone (1-10 nM) enhanced the relative abundance of SP-A mRNA. Despite stimulation of SP-A mRNA, intracellular SP-A content was unaltered or inhibited by dexamethasone. SP-B and SP-C mRNAs and synthesis of the SP-B and SP-C precursors were markedly induced by dexamethasone. ProSP-B was synthesized and secreted primarily as an Mr 42,000-46,000 polypeptide. Proteolysis of the proSP-B resulted in the generation of endoglycosidase F-sensitive Mr = 19,000-21,000 and 25,000-27,000 peptides, which were detected both intra- and extracellularly. SP-C proprotein of Mr = 22,000 and smaller SP-C fragments were detected intracellularly but were not detected in the media. Mature forms of SP-B (Mr = 8,000) and SP-C (Mr = 4,000) were not detected. Glucocorticoids directly enhance the relative synthesis and mRNA of the surfactant proteins SP-A, SP-B, and SP-C. Discrepancies among SP-A mRNA, its de novo synthesis, and cell content suggest that glucocorticoid may alter both pre- and posttranslational factors modulating SP-A expression.
O'Reilly
M A
MA
Division of Pulmonary Biology, Children's Hospital, Cincinnati, Ohio 45267-0541.
Gazdar
A F
AF
Clark
J C
JC
Pilot-Matias
T J
TJ
Wert
S E
SE
Hull
W M
WM
Whitsett
J A
JA
D000230:Adenocarcinoma; D002460:Cell Line; D004273:DNA, Neoplasm / Q000235:genetics; D003907:Dexamethasone / Q000494:pharmacology*; D006801:Humans; D008175:Lung Neoplasms; D008715:Methionine / Q000378:metabolism; D008854:Microscopy, Electron; D011663:Pulmonary Surfactants / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification; D013462:Sulfur Radioisotopes; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure
D004273:DNA, Neoplasm; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; D013462:Sulfur Radioisotopes; D003907:Dexamethasone; D008715:Methionine