cAMP-dependent protein kinase and protein phosphorylation in developing rat lung

Protein kinase activity that is dependent on 3',5'-Cyclic adenosine monophosphate (cAMP-PK), [3H]cAMP binding, and cAMP-dependent protein phosphorylation were identified and partially characterized in cytosolic preparations of rat lung from day 18 of gestation to adulthood. Major cAMP-dependent phosphoproteins in lung preparations were compared to those in cytosol from purified Type II epithelial cells. Both Type I and Type II regulatory subunits of cAMP-PK were identified in fetal and adult lung. Inhibition of specific [3H]cAMP binding to lung cytosol (to the regulatory subunit of the cAMP-dependent protein kinase) followed the order of potency: cAMP greater than cGMP; adenosine, ADP, and ATP were inactive. Scatchard plots of saturation experiments with [3H]cAMP and lung cytosol were linear. Dissociation constant (KD) for cAMP binding was approximately 2-3 nM, and did not change significantly with age. In contrast, binding capacity varied significantly during development and age-related changes in binding capacity were associated with similar changes in cAMP-dependent histone kinase activity. Both [3H]cAMP binding and cAMP-dependent protein kinase activity decreased slightly before birth, reached maximal activity during the suckling period, and decreased in adulthood. cAMP enhanced histone kinase activity in rat lung cytosol at all ages studied, from day 18 of gestation to adulthood. cAMP also specifically enhanced phosphorylation of several endogenous cytosolic proteins that were identified by autoradiography after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Major proteins whose phosphorylation was selectively enhanced by cAMP or inhibited by protein kinase inhibitor were approximately Mr = 260,000, 240,000, 97,000, 56,000, 44,000, and 28,000.(ABSTRACT TRUNCATED AT 250 WORDS)