AJP - Lung Cellular and Molecular Physiology, Vol 267, Issue 1 25-L32, Copyright © 1994 by American Physiological Society
Increased expression of CTP:phosphocholine cytidylyltransferase in maturing type II cells
M. Hogan, L. J. Zimmermann, J. Wang, M. Kuliszewski, J. Liu and M. Post
Department of Paediatrics, Hospital for Sick Children Research Institute, University of Toronto, Ontario, Canada.
We previously reported that phosphatidylcholine synthesis increased in
fetal rat lung type II cells with advancing gestation. This increase was
accompanied by an increase in CTP:phosphocholine cytidylyltransferase
activity, which catalyses a rate regulatory step in de novo
phosphatidylcholine synthesis by fetal type II cells. To determine whether
this increase in cytidylyltransferase activity is due to an increase in
cytidylyltransferase protein levels, the gene and protein expression of
cytidylyltransferase was investigated in maturing type II cells. The
cytidylyltransferase cDNA was cloned from fetal rat type II cells and
showed 99% sequence homology with rat liver cDNA. The cDNA detected two
mRNA transcripts (1.8 and 7.5 kb) in fetal rat lung. By
reverse-transcriptase polymerase chain reaction (RT-PCR) analysis,
cytidyltransferase mRNA content increased three-fold in fetal type II cells
with advancing gestation, whereas cytidylyltransferase mRNA levels in
fibroblasts remained constant. An antibody against rat liver
cytidylyltransferase was used to assess cytidylyltransferase protein.
Western blotting revealed that cytidylyltransferase protein content
increased threefold in the microsomal fraction of type II cells with
advancing gestation. The enzyme protein levels in the cytosolic fraction
did not significantly change with development. Enzyme activity studies
confirmed these latter observations. We conclude that the increase in
surfactant phosphatidylcholine synthesis by type II cells at late fetal
gestation is due in part to an increase in the amount of
cytidylyltransferase protein.
