CYCLIC-AMP-DEPENDENT PROTEIN-KINASES AND HUMAN TROPHOBLAST CELL-DIFFERENTIATION IN-VITRO

Human trophoblast cells offer a unique in vitro model for the study of aspects of the dynamic processes occurring during cell fusion and syn cytium formation. In the human placenta, mononuclear cytotrophoblasts aggregate and fuse to form a multinucleated syncytiotrophoblast. In vi tro, the addition of cyclic AMP analogs, 8-bromo-cyclic-AMP or Sp-8-br omo-cyclic AMPS, promotes syncytiotrophoblast formation, as shown by t he disappearance of immunostained E-cadherin and desmoplakin, and incr eased numbers of nuclei per syncytium. An antagonist of cyclic AMP, Rp -8-bromo-cyclic AMPS, and an inhibitor of the cyclic All IP-dependent protein kinase catalytic subunit, H-89, impair cell fusion, This led u s to study the pattern of expression and subcellular localization of c yclic-AMP-dependent protein kinase subunits during syncytium formation . Cytotrophoblasts expressed the RI alpha and RII alpha regulatory sub units and the C alpha and C beta catalytic subunits, RI alpha was down -regulated during syncytium formation, No change in RII omega. protein levels was observed, but there was a drastic subcellular redistributi on. RII alpha located in the Golgi-centrosomal area of cytotrophoblast s was scattered throughout the cytoplasm of the syncytiotrophoblast. I nterestingly, an accumulation of RII alpha was observed underneath the epical membrane of syncytiotrophoblast in vitro and in situ This sugg ests a key role of cyclic AMP-dependent protein kinase type II alpha d uring cell fusion and microvilli formation, both of which are essentia l for the secretory and transfer functions of the syncytiotrophoblast.