Glucocorticoid enhances pulmonary surfactant protein B gene transcription.
The effect of glucocorticoid on the regulation of pulmonary surfactant protein B (SP-B) synthesis was studied in a human pulmonary adenocarcinoma cell line. Northern blot analysis demonstrated a marked increase in SP-B mRNA expression after treatment with dexamethasone for 48 h. Actinomycin D, puromycin, or cycloheximide blocked the induction of SP-B mRNA by glucocorticoid. Nuclear run-on experiments demonstrated that the effects of dexamethasone on SP-B mRNA were due in part to increased transcription of the SP-B gene. However, during this time period, there was a discrepancy between SP-B gene transcription, which was increased only 2- to 4-fold, and SP-B mRNA, which increased 60- to 150-fold after treatment with dexamethasone. In the presence of actinomycin D, SP-B mRNA was relatively stable, decreasing slowly in the presence or absence of glucocorticoid. In contrast to the relative stability of SP-B mRNA in the presence of actinomycin D, SP-B mRNA was markedly decreased after exposure to puromycin, supporting the premise that continued protein synthesis, rather than transcription alone, is required for maintenance of SP-B mRNA levels. Induction of SP-B expression by glucocorticoids was dependent on enhanced SP-B gene transcription and was also dependent on continued protein synthesis. The discrepancy between the relative enhancement of SP-B transcription and SP-B mRNA suggests that posttranscriptional factors influence SP-B expression in this cell line.
O'Reilly
M A
MA
Division of Pulmonary Biology, Children's Hospital Medical Center, Cincinnati, Ohio 45267-0541.
Clark
J C
JC
Whitsett
J A
JA
D000230:Adenocarcinoma; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003001:Cloning, Molecular; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms; D009693:Nucleic Acid Hybridization; D011510:Proteolipids / Q000235:genetics*; D011663:Pulmonary Surfactants / Q000235:genetics*; D011691:Puromycin / Q000494:pharmacology; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects*
D011510:Proteolipids; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; D003609:Dactinomycin; D011691:Puromycin; D003907:Dexamethasone; D003513:Cycloheximide