Expression and glucocorticoid regulation of surfactant protein C in human fetal lung.
The hydrophobic surfactant protein C (SP-C) is known to modulate the biophysical properties of surfactant phospholipid. Although SP-C mRNA has been demonstrated in human fetal lung, there is limited information regarding developmental expression and processing of proSP-C protein. Two epitope-specific human proSP-C antisera, anti-hCPROSP-C (His59-Ser72) and anti-hCTERMSP-C (Gly162-Gly175), were generated to complement previously produced anti-NPROSP-C (Met10-Gln23) for the study of proSP-C expression in human fetal lung. Western blotting and immunocytochemistry detected expression of proSP-C protein by 12-16 wk of gestation. ProSP-C immunoreactivity of preculture lung, limited to expression of proSP-C21 in airway epithelial cells, was markedly enhanced by culture of lung explants in dexamethasone. To examine synthesis of proSP-C, homogenates from explants were labeled with 35S-Met/Cys for 0.5-4 h. Immunoprecipitation with anti-NPROSP-C detected 35S-proSP-C21 by 30 min and, after 2 h of labeling, there was a 15-fold increase in 35S-proSP-C21 in dexamethasone-treated lungs versus controls. Synthesis of proSP-C21 was followed by the appearance of a 24-kD form and smaller processing intermediates including 6-10-kD forms. Posttranslational processing of proSP-C21 was not observed in control explants. SP-C(6-10) were not recognized by either anti-CPROSP-C or anti-hCTERMSP-C. These results indicate that low level expression of proSP-C protein first occurs in epithelial cells early in the second trimester and that expression can be enhanced by dexamethasone. Initial posttranslational processing of human proSP-C involves modification of proSP-C21 to SP-C24 and subsequent proteolysis of C-terminal propeptide domains. We speculate that absence of low Mr intermediates in unstimulated second trimester fetal lung tissue reflects developmental and glucocorticoid dependent regulation of proSP-C21 synthesis and posttranslational processing.
Solarin
K O
KO
Department of Pediatrics Children's Hospital of Philadelphia, Pennsylvania 19104, USA.
Ballard
P L
PL
Guttentag
S H
SH
Lomax
C A
CA
Beers
M F
MF
D000888:Antibodies, Anti-Idiotypic / Q000032:analysis / Q000276:immunology; D000918:Antibody Specificity; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D015153:Blotting, Western; D002478:Cells, Cultured / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D005333:Fetus / Q000187:drug effects* / Q000378:metabolism*; D015870:Gene Expression; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics; D005865:Gestational Age; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D007106:Immune Sera / Q000276:immunology; D007150:Immunohistochemistry; D008168:Lung / Q000166:cytology / Q000196:embryology* / Q000378:metabolism*; D011247:Pregnancy; D014176:Protein Biosynthesis / Q000235:genetics / Q000276:immunology; D011498:Protein Precursors / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D011499:Protein Processing, Post-Translational; D011510:Proteolipids / Q000096:biosynthesis* / Q000187:drug effects* / Q000276:immunology; D011663:Pulmonary Surfactants / Q000096:biosynthesis* / Q000187:drug effects* / Q000276:immunology
D000888:Antibodies, Anti-Idiotypic; D018931:Antineoplastic Agents, Hormonal; D005938:Glucocorticoids; D007106:Immune Sera; D011498:Protein Precursors; D011510:Proteolipids; D011663:Pulmonary Surfactants; D003907:Dexamethasone