Induction of surfactant protein in fetal lung. Effects of cAMP and dexamethasone on SAP-35 RNA and synthesis.
Synthesis of surfactant-associated glycoprotein of Mr = 30,000-35,000 (SAP-35) was induced in explant culture of human fetal lung obtained from 8 to 24 weeks of gestation. SAP-35 synthesis and content increased markedly during 1-5 days in organ culture in association with the morphologic maturation of Type II epithelial cells and the appearance of lamellar bodies. [35S] Methionine labeling of the explants and subsequent immunoprecipitation of SAP-35 demonstrated distinct high-mannose precursors and sialylated SAP-35 forms as early in culture as SAP-35 synthesis was detectable. The increase in SAP-35 synthesis was associated with increased SAP-35 RNA of 2.1 kilobases as assessed by hybridization assay with [32P]cDNA specific for human SAP-35. Specific SAP-35 RNA increased during organ culture and both SAP-35 content and SAP-35 RNA increased in the absence of exogenous hormones in 2% carbon-stripped fetal calf serum. SAP-35 content and synthesis was stimulated by 8-Br-cAMP. Addition of 100 microM 8-Br-cAMP, enhanced both the concentration of SAP-35 protein and the SAP-35 RNA as assessed by hybridization assay. In contrast, treatment of the explants with dexamethasone was associated with decreased SAP-35 protein synthesis, SAP-35 content, and decreased SAP-35 RNA levels compared to untreated explants. Inhibition by dexamethasone occurred at all gestational ages tested, was dose-dependent, and detectable within 24-48 h during organ culture. Dexamethasone significantly inhibited both basal and cAMP-induced SAP-35 synthesis. Induction of pulmonary surfactant protein (SAP-35) synthesis during organ culture of human fetal lung was associated with increased SAP-35 RNA. SAP-35 synthesis and SAP-35 RNA were inhibited by dexamethasone and enhanced cAMP.
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008168:Lung / Q000187:drug effects / Q000196:embryology*; D008715:Methionine / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D009924:Organ Culture Techniques; D011247:Pregnancy; D011510:Proteolipids / Q000096:biosynthesis / Q000235:genetics*; D037662:Pulmonary Surfactant-Associated Protein A / Q000031:analogs & derivatives*; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000096:biosynthesis / Q000235:genetics*; D012313:RNA / Q000378:metabolism*
D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; C445842:SFTPA1 protein, human; D015124:8-Bromo Cyclic Adenosine Monophosphate; D012313:RNA; D003907:Dexamethasone; D008715:Methionine; D000242:Cyclic AMP