cAMP increases synthesis of surfactant-associated protein A by perfused rat lung.
Synthesis and secretion of surfactant-associated protein were studied in isolated rat lungs perfused with [3H]phenylalanine or [35S]methionine in synthetic medium. Surfactant was isolated by lung lavage and density-gradient centrifugation followed by dialysis to remove unincorporated amino acid and extraction with ethanol-ether to yield a delipidated protein fraction. Incorporation of [3H]phenylalanine into the delipidated surfactant protein fraction showed a lag phase of approximately 3 h followed by progressive increase over the next 3 h at a rate of 1.6 nmol.mg protein-1.h-1. With 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP, 0.1 mM) added to the perfusate, the incorporation rate between 3 and 6 h was increased by 75%. 3H specific activity in a delipidated lamellar body-rich fraction isolated from lung homogenates was unchanged by 8-BrcAMP at 3 h but was increased by 45% at 6 h. The major peak of radioactivity on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of surfactant and lamellar bodies corresponded to proteins of 27-36 kDa that were identified as surfactant protein A (SP-A) by immunoblot. In the presence of 8-BrcAMP during 6 h of perfusion, specific activity of 35S-labeled SP-A in immunoprecipitated protein was increased by 93% and the SP-A mRNA content of lung was increased 145%. These results show that isolated perfused lungs synthesize and secrete surfactant-associated proteins and that the presence of a permeable cAMP analogue in the lung perfusate leads to increased secretion followed by induction of synthesis for SP-A.
Fisher
A B
AB
Institute for Environmental Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104-6068.
Arad
I
I
Dodia
C
C
Chander
A
A
Feinstein
S I
SI
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000199:Actins / Q000235:genetics; D000818:Animals; D000242:Cyclic AMP / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D007700:Kinetics; D008168:Lung / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010477:Perfusion; D010649:Phenylalanine / Q000378:metabolism; D011510:Proteolipids / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification; D051381:Rats; D011919:Rats, Inbred Strains
D000199:Actins; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; D015124:8-Bromo Cyclic Adenosine Monophosphate; D010649:Phenylalanine; D012313:RNA; D003513:Cycloheximide; D000242:Cyclic AMP