Transcription and mRNA stability regulate developmental and hormonal expression of rabbit surfactant protein B gene.
Surfactant protein B (SP-B), a hydrophobic protein of pulmonary surfactant, is essential for the surface tension-reducing properties of surfactant. In the present study, we isolated and characterized cDNAs encoding rabbit SP-B, and used transcription run-on assays and Northern blot analysis to investigate the role of transcriptional and posttranscriptional mechanisms in the developmental and cAMP and dexamethasone induction of SP-B mRNA. We found two forms of SP-B cDNAs that differed by an insertion of 69 nucleotides in the 3' untranslated regions. We found that transcription across the SP-B gene is nonequimolar and the 3' end of the gene has high levels of antisense transcription. SP-B gene transcription and SP-B mRNA levels increased during fetal lung development. However, increased SP-B mRNA levels could not be accounted for primarily on the basis of increased transcription. These results suggested that enhanced SP-B gene transcription and enhanced SP-B mRNA stability mediate developmental induction of SP-B gene. In rabbit fetal lung in vitro, both dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) and dexamethasone increased SP-B mRNA levels. DBcAMP-dependent increase in SP-B mRNA levels resulted from increased SP-B gene transcription, whereas dexamethasone-dependent increase resulted from combined effects on increased SP-B gene transcription and SP-B mRNA stability. In tissues treated with dexamethasone the half-life (t1/2) of SP-B mRNA increased > 2.5-fold (t1/2 control = 9 h; t1/2 dex-treated = 25 h). These data show that both transcription and mRNA stability regulate induction of SP-B gene expression during fetal lung development and by cAMP and dexamethasone in fetal lung in vitro.
Margana
R K
RK
Department of Molecular Biology, University of Texas Health Science Center at Tyler 75710.
Boggaram
V
V
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003994:Bucladesine / Q000494:pharmacology; D018076:DNA, Complementary / Q000737:chemistry / Q000302:isolation & purification; D003907:Dexamethasone / Q000494:pharmacology; D004355:Drug Stability; D005260:Female; D005786:Gene Expression Regulation; D005865:Gestational Age; D008168:Lung / Q000196:embryology* / Q000254:growth & development / Q000378:metabolism; D008969:Molecular Sequence Data; D011247:Pregnancy; D011510:Proteolipids / Q000737:chemistry / Q000235:genetics*; D011663:Pulmonary Surfactants / Q000737:chemistry / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D011817:Rabbits; D017422:Sequence Analysis, DNA; D013047:Specific Pathogen-Free Organisms; D014158:Transcription, Genetic
D018076:DNA, Complementary; D011510:Proteolipids; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; D003994:Bucladesine; D003907:Dexamethasone