PHOSPHOINOSITIDASE-C ISOZYMES IN SAOS-2 CELLS - IMMUNOCYTOCHEMICAL DETECTION IN NUCLEAR AND CYTOPLASMIC COMPARTMENTS

SaOS-2 cell line presents osteoblastic characteristics which can be mo dulated by specific agonists involving also phosphoinositide breakdown . In order to determine whether SaOS-2 cells display a phosphoinositid e signalling system not only at the cytosol-cell membrane level but al so, as recently reported for other cell lines, at the nuclear level, a study has been performed to evaluate the phosphoinositidase C (PIC) a ctivity and to localize different isoforms of PIC in nuclear and cytop lasmic compartments. By immunochemicals methods, and by confocal and e lectron microscope immunocytochemistry, both PIC beta(1) and gamma(1) have been detected in the nucleus, while only PIC gamma(1) was found i n the cytoplasm. A specific association with the inner nuclear matrix has been demonstrated for PIC beta(1) and gamma(1); this latter result ed, on the other hand, in relationship with cytoskeletal filaments aft er high salt extraction. These findings suggest that these enzymes are not completely soluble but functionally related with cytoskeletal and nucleoskeletal structures.