Adenosine 3',5'-monophosphate (cAMP)-binding protein and cAMP-dependent protein kinase in human placenta.
cAMP modulates estrogen, hCG, and lactate syntheses by human placenta, cAMP presumably exerts its major intracellular effect by binding to cAMP-dependent protein kinase (cAMP-PK), which, in turn, phosphorylates regulatory proteins within the target cell. cAMP binding and cAMP-PK have not been previously identified in placenta. [3H]cAMP binding to crude cytosol fractions of term placenta was rapid, saturable, and reversible. Scatchard analyses of saturation experiments of [3H]cAMP binding to placental cytosol were linear (Kd = 1.13 +/- 0.11 x 10(-8) M; n = 5). The binding capacity was 1.27 +/- 0.18 pmol/mg protein. Competition for the [3H]cAMP-binding site followed the potency order cAMP much greater than cGMP much greater than (Bu)2cAMP, analogous to cAMP binding to cAMP-PK in other tissues. ADP, ATP, and adenosine did not compete for the [3H]cAMP-binding site. cAMP significantly enhanced phosphorylation of histone protein by placental cytosol (activity ratio, 0.57 +/- 0.04; P less than 0.01). Two peaks of [3H]cAMP binding and coincident cAMP-PK activity were identified by DEAE-cellulose column chromatography of placental cytosol corresponding to classical type I and type II cAMP-PK. While the majority of the cAMP-PK was found in placental cytosol, cAMP-PK was also demonstrated in crude microsomal and microvillous brush border membranes of human placenta after solubilization with Triton X-100 (P less than 0.05). Regulation of placental function by catecholamines and other hormones known to mediate cAMP levels may be accomplished through the phosphorylation of cellular proteins by cAMP-dependent protein kinases.
D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002848:Chromatography, DEAE-Cellulose; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology*; D002373:Cyclic AMP Receptor Protein; D003600:Cytosol / Q000201:enzymology; D005260:Female; D006657:Histones / Q000378:metabolism; D006801:Humans; D008861:Microsomes / Q000201:enzymology; D008871:Microvilli / Q000201:enzymology; D010766:Phosphorylation; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011494:Protein Kinases / Q000378:metabolism*
D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D006657:Histones; D000242:Cyclic AMP; D011494:Protein Kinases