title: Glucocorticoid regulation of human pulmonary surfactant protein-B (SP-B) mRNA stability is independent of activated glucocorticoid receptor.
abstract: Adequate expression of surfactant protein-B (SP-B) is critical in the function of pulmonary surfactant to reduce alveolar surface tension. Expression of SP-B mRNA is restricted to specific lung-airway epithelial cells, and human SP-B mRNA stability is increased in the presence of the synthetic glucocorticoid dexamethasone (DEX). Although the mechanism of SP-B mRNA stabilization by DEX is unknown, studies suggest involvement of the glucocorticoid receptor (GR). We developed a dual-cistronic plasmid-based expression assay in which steady-state levels of SP-B mRNA, determined by Northern analysis, reproducibly reflect changes in SP-B mRNA stability. Using this assay, we found that steady-state levels of SP-B mRNA increased greater than twofold in transfected human-airway epithelial cells (A549) incubated with DEX (10(-7) M). DEX-mediated changes in SP-B mRNA levels required the presence of the SP-B mRNA 3'-untranslated region but did not require ongoing protein synthesis. The effect of DEX on SP-B mRNA levels was dose dependent, with maximal effect at 10(-7) M. DEX increased levels of SP-B mRNA in cells lacking GR, and the presence of the GR antagonist RU486 did not interfere with the effect of DEX. Surprisingly, other steroid hormones (progesterone, estradiol, and vitamin D; 10(-7) M) significantly increased SP-B mRNA levels, suggesting a common pathway of steroid hormone action on SP-B mRNA stability. These results indicate that the effect of DEX to increase SP-B mRNA stability is independent of activated GR and suggests that the mechanism is mediated by posttranscriptional or nongenomic effects of glucocorticoids.
authors.affiliation: Department of Pediatrics, Division of Neonatal-Perinatal Medicine, University of Texas Health Sciences Center at Houston, USA.
authors.forename: Ceá C
authors.initials: CC
authors.lastname: Tillis
authors.forename: Helen W
authors.initials: HW
authors.lastname: Huang
authors.forename: Weizhen
authors.initials: W
authors.lastname: Bi
authors.forename: Su
authors.initials: S
authors.lastname: Pan
authors.forename: Shirley R
authors.initials: SR
authors.lastname: Bruce
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Alcorn
mesh_terms: D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D015152:Blotting, Northern; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006367:HeLa Cells; D006727:Hormone Antagonists / Q000494:pharmacology; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015735:Mifepristone / Q000494:pharmacology; D037701:Pulmonary Surfactant-Associated Protein B / Q000235:genetics*; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects*; D020871:RNA Stability / Q000187:drug effects*; D012333:RNA, Messenger / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000187:drug effects; D014471:Umbilical Veins / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
chemical_list: D000893:Anti-Inflammatory Agents; D006727:Hormone Antagonists; D037701:Pulmonary Surfactant-Associated Protein B; D012333:RNA, Messenger; D015735:Mifepristone; D003907:Dexamethasone