Glucocorticoid regulation of human pulmonary surfactant protein-B mRNA stability involves the 3'-untranslated region.
Expression of pulmonary surfactant, a complex mixture of lipids and proteins that acts to reduce alveolar surface tension, is developmentally regulated and restricted to lung alveolar type II cells. The hydrophobic protein surfactant protein-B (SP-B) is essential in surfactant function, and insufficient levels of SP-B result in severe respiratory dysfunction. Glucocorticoids accelerate fetal lung maturity and surfactant synthesis both experimentally and clinically. Glucocorticoids act transcriptionally and post-transcriptionally to increase steady-state levels of human SP-B mRNA; however, the mechanism(s) by which glucocorticoids act post-transcriptionally is unknown. We hypothesized that glucocorticoids act post-transcriptionally to increase SP-B mRNA stability via sequence-specific mRNA-protein interactions. We found that glucocorticoids increase SP-B mRNA stability in isolated human type II cells and in nonpulmonary cells, but do not alter mouse SP-B mRNA stability in a mouse type II cell line. Deletion analysis of an artificially-expressed SP-B mRNA indicates that the SP-B mRNA 3'-untranslated region (UTR) is necessary for stabilization, and the region involved can be restricted to a 126-nucleotide-long region near the SP-B coding sequence. RNA electrophoretic mobility shift assays indicate that cytosolic proteins bind to this region in the absence or presence of glucocorticoids. The formation of mRNA:protein complexes is not seen in other regions of the SP-B mRNA 3'-UTR. These results indicate that a specific 126-nucleotide region of human SP-B 3'-UTR is necessary for increased SP-B mRNA stability by glucocorticoids by a mechanism that is not lung cell specific and may involve mRNA-protein interactions.
Huang
Helen W
HW
Department of Pediatrics, University of Texas-Houston Medical School, 6431 Fannin, suite 3.222, Houston, TX 77030, USA.
Bi
Weizhen
W
Jenkins
Gaye N
GN
Alcorn
Joseph L
JL
D020413:3' Untranslated Regions / Q000235:genetics*; D000818:Animals; D020029:Base Pairing / Q000187:drug effects; D001483:Base Sequence; D001667:Binding, Competitive / Q000187:drug effects; D002469:Cell Separation; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology*; D006207:Half-Life; D006801:Humans; D051379:Mice; D011485:Protein Binding / Q000187:drug effects; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D037701:Pulmonary Surfactant-Associated Protein B / Q000235:genetics* / Q000378:metabolism; D020871:RNA Stability / Q000187:drug effects*; D014162:Transfection
D020413:3' Untranslated Regions; D005938:Glucocorticoids; D037701:Pulmonary Surfactant-Associated Protein B; D003609:Dactinomycin; D003907:Dexamethasone