Cytoplasmic and nuclear localization sites of phosphatidylinositol 3-kinase in human osteosarcoma sensitive and multidrug-resistant Saos-2 cells
SaOS-2 cell line presents osteoblastic characteristics which can be modulated by specific agonists involving also phosphoinositide breakdown. In order to determine whether SaOS-2 cells display a phosphoinositide signalling system not only at the cytosol-cell membrane level but also, as recently reported for other cell lines, at the nuclear level, a study has been performed to evaluate the phosphoinositidase C (PIC) activity and to localize different isoforms of PIC in nuclear and cytoplasmic compartments. By immunochemicals methods, and by confocal and electron microscope immunocytochemistry, both PIC beta 1 and gamma 1 have been detected in the nucleus, while only PIC gamma 1 was found in the cytoplasm. A specific association with the inner nuclear matrix has been demonstrated for PIC beta 1 and gamma 1; this latter resulted, on the other hand, in relationship with cytoskeletal filaments after high salt extraction. These findings suggest that these enzymes are not completely soluble but functionally related with cytoskeletal and nucleoskeletal structures.