Differential glucocorticoid regulation of the pulmonary hydrophobic surfactant proteins SP-B and SP-C.
Glucocorticoids increase expression of the genes for the pulmonary surfactant-associated proteins SP-B and SP-C in fetal lung both in vivo and in vitro. To examine the mechanism of these effects, we studied induction of SP-B and SP-C mRNAs in human fetal lung cultured as explants. Both mRNA levels rose rapidly in response to 100 nM dexamethasone (Dex), with a faster response for SP-B: maximal levels of induction were achieved in < or = 12 h for SP-B (3.5-fold versus control) versus approximately 24 h for SP-C mRNA (35-fold versus control). Cycloheximide (2.5 micrograms/ml) did not affect glucocorticoid induction of SP-B mRNA but markedly decreased induction of SP-C mRNA. In control cultures, cycloheximide did not significantly reduce levels of either transcript. In nuclear run-on assays, Dex increased the rate of gene transcription for both SP-B (2.8 +/- 0.3-fold versus control, n = 4) and SP-C (10- to 30-fold). Using actinomycin D to assess mRNA stability, the t1/2 of SP-B mRNA was increased from 7.5 +/- 0.4 h to 18.8 +/- 2.9 h by Dex treatment (P < 0.05), whereas the t1/2 of SP-C mRNA was not affected (9.3 +/- 1.7 h versus 8.1 +/- 1.2 h; NS). A similar increase in SP-B mRNA t1/2 with Dex (from 6 h to 19 h) was observed in label-chase studies with [3H]uridine. We conclude that glucocorticoids regulate the hydrophobic surfactant proteins of alveolar type II cells by different mechanisms: induction of SP-B is a primary response and includes an increase in both transcription rate and mRNA stability, whereas induction of SP-C is a secondary process, requiring ongoing protein synthesis, involving increased transcription rate without a change in mRNA stability.
Venkatesh
V C
VC
Department of Pediatrics, University of Pennsylvania School of Medicine, Children's Hospital of Philadelphia 19104.
Iannuzzi
D M
DM
Ertsey
R
R
Ballard
P L
PL
D046508:Culture Techniques; D003513:Cycloheximide / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D005938:Glucocorticoids / Q000502:physiology*; D006801:Humans; D008168:Lung / Q000196:embryology / Q000378:metabolism; D011510:Proteolipids / Q000235:genetics*; D011663:Pulmonary Surfactants / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D014158:Transcription, Genetic
D005938:Glucocorticoids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; D003907:Dexamethasone; D003513:Cycloheximide