Spermine-enhanced protein phosphorylation in human placenta.
Polyamines are known to have a role in cell proliferation, differentiation, and protein synthesis. During pregnancy, major changes in polyamine levels occur in maternal serum, amniotic fluid, and placental tissue. Polyamine-activated phosphorylation has recently been proposed as a mechanism by which polyamines may regulate metabolic processes in target tissues. Polyamine-activated protein phosphorylation has not been studied in placenta. Homogenate membrane and cytosol fractions from human placenta were subjected to an endogenous protein phosphorylation assay using [gamma-32P]ATP in the presence and absence of the polyamines, spermine and spermidine, and the diamine, putrescine. Protein phosphorylation was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. When compared to basal levels, spermine (10(-3) M) significantly (P less than 0.001) stimulated 32P incorporation into phosphoproteins having molecular weights of 55,000 and 105,000. At this concentration spermidine and putrescine failed to stimulate phosphorylation. Half-maximal 32P incorporation was observed with 3.7 +/- 1.25 X 10(-4) M spermine. Polylysine enhanced the phosphorylation of phosphoproteins of the same molecular weight as those enhanced by spermine. Heparin and high Mg2+ inhibited spermine-induced phosphorylation. cAMP and Ca2+ did not stimulate phosphorylation of the spermine-dependent phosphoproteins. Spermine, however, acted as an antagonist for cAMP-dependent phosphorylation of a Mr 45,000 phosphoprotein.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008970:Molecular Weight; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010920:Placenta / Q000187:drug effects / Q000378:metabolism*; D011107:Polylysine / Q000494:pharmacology; D011247:Pregnancy; D011700:Putrescine / Q000494:pharmacology; D013095:Spermidine / Q000494:pharmacology; D013096:Spermine / Q000494:pharmacology*
D010750:Phosphoproteins; D011107:Polylysine; D013096:Spermine; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D013095:Spermidine; D011700:Putrescine