Cholinephosphate cytidylyltransferase in fetal rat lung cells: activity and subcellular distribution in response to dexamethasone, triiodothyronine, and fibroblast-conditioned medium.
The initiation of pulmonary surfactant synthesis during fetal development has been shown to be under hormonal control. Using cultured lung cells isolated from 19-day-gestation fetal rats, we evaluated the effects of various hormones on the activity and subcellular distribution of cholinephosphate cytidylyltransferase, a rate-controlling enzyme in phosphatidylcholine synthesis. The cells were incubated in medium containing 10% carbon-stripped fetal bovine serum to which dexamethasone, triiodothyronine, and/or conditioned medium from dexamethasone-treated fetal rat lung fibroblasts were added for 48 h. Dexamethasone and fibroblast-conditioned medium increased microsomal enzyme activity 169% +/- 6% (mean +/- SE, p less than 0.01) and 150% +/- 2% (p less than 0.05) over control levels, respectively. Further, dexamethasone increased cytosolic specific activity 160% +/- 17% (p less than 0.05). Addition of T3 to the fibroblast-conditioned medium caused a further increase in microsomal activity, but T3 alone had no effect. Increased microsomal cytidylyltransferase activity correlated with an increased rate of [3H]choline incorporation into disaturated phosphatidylcholine. Hormonal induced increases in enzyme activity were not adequately explained by simple translocation of enzyme from cytosol to microsomes. Cycloheximide (5 micrograms/ml) inhibited enzyme stimulation by dexamethasone and fibroblast-conditioned medium, suggesting that protein synthesis of new enzyme or regulatory proteins is involved. We conclude that hormones modulate cytidylyltransferase activity of isolated fetal lung cells. Dexamethasone and fibroblast-conditioned medium exert their major effects by stimulating microsomal activity.
Viscardi
R M
RM
Department of Pediatrics, University of Michigan, Ann Arbor.
Weinhold
P A
PA
Beals
T M
TM
Simon
R H
RH
D000818:Animals; D002478:Cells, Cultured; D019916:Choline-Phosphate Cytidylyltransferase; D003470:Culture Media / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D005333:Fetus / Q000166:cytology; D005347:Fibroblasts / Q000187:drug effects; D007700:Kinetics; D008168:Lung / Q000166:cytology / Q000196:embryology / Q000201:enzymology*; D009713:Nucleotidyltransferases / Q000032:analysis*; D010713:Phosphatidylcholines / Q000032:analysis; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology; D014284:Triiodothyronine / Q000494:pharmacology*
D003470:Culture Media; D010713:Phosphatidylcholines; D014284:Triiodothyronine; D003907:Dexamethasone; D003513:Cycloheximide; D009713:Nucleotidyltransferases; D019916:Choline-Phosphate Cytidylyltransferase