CYTOSKELETAL REORGANIZATION INDUCED BY RETINOIC ACID TREATMENT OF HUMAN ENDOMETRIAL ADENOCARCINOMA (RL95-2) CELLS IS CORRELATED WITH ALTERATIONS IN PROTEIN-KINASE-C-ALPHA

We have shown previously that treatment of human endometrial adenocarc inoma RL95-2) cells with either 13-cis or all-trans retinoic acid resu lts in reorganization of actin filaments, indicating reversion to a st ationary phenotype. In the present study, we investigated the role of protein kinase C (PKC) in this process. Treatment of cells with PKC in hibitors (staurosporine, bisindolylmaleimide, or Go6976) resulted in m orphological alterations and reorganization of actin filaments similar to retinoic-acid-treated cells. For example, RL95-2 cells treated wit h staurosporine flattened, exhibited cell surface extensions and some actin filaments. Bisindolylmaleimide-treated cells flattened, and acti n filaments reorganized similar to retinoic-acid-treated cells. RL95-2 cells treated with Go6976, which inhibits only PKC alpha, beta, and g amma, exhibited many cell surface extensions and some actin filament r eorganization. We then investigated whether retinoic acid affected the subcellular localization of PKC-alpha. In control cells, PKC-alpha wa s mainly evident as diffuse cytoplasmic immunostaining, with a small p ercentage of total PKC-alpha also evident in the plasma membrane. Reti noic acid treatment dramatically altered PKC-alpha localization, since a more distinct cytoplasmic and perinuclear staining pattern was appa rent. Western blot analysis confirmed these results, since the amount of cytosolic PKC-alpha increased following retinoic acid treatment. Th us, retinoic-acid-induced endometrial differentiation may be associate d with alterations in PKC-alpha localization and signaling.